The Human Eye in Photographic Terms
Related Links:
Schneider Website
cf. Schneider White Paper on Digital Optics for eye response curves 40 lpmm.. [12/2000]
Supervision for Human Eyes (deformable lenses..)[1/2001]
Vision - failing eyesight..
Related Postings
From: cg081@torfree.net (Martin Tai)
Subject: Re: What is the speed of the human eye?
Date: Thu, 26 Nov 1998
Mr. M.J. Lush (mlush@hgmp.mrc.ac.uk) wrote:
: Its often said that the eye is like a camera if this is
: so what is the effective f stop of the iris and how fast a film
: is the retina?
: I ask this question out of general interest and to get a
: start point for estermating exposure in low light photography.
: (if its dark my iris will by fully open so what I see is
: equivilant to a 'retina ASA' film seen through an f-iris lens)
: --
: Michael
The effective focal length of human eye is between 13-16mm, and the
effective numerical aperture is about f3 to f4.
As for the retina ASA, it far exceeds any existing high speed
films.
A Russian scientist and academician tested the sensitivity of
retina, it can sense as few as a dozen photons.
martin tai
Date: 2 Jan 2000
From: Philipp Pagel pagel@abraxas.magic.lan
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Aperture of Human Eye
Hi!
> This may be a dumb question, but what would the aperture of the human
> eye be??? I realize the eyeball itself changes shape to accommodate
> varying focal lengths, but is there anyone out there who knows how the
> physics of vision relate to camera equipment.
Not the eyeball but the lens changes shape for focusing.
If I remember correctly (I don't have my books here) the total refractive
power of the optical system of a human eye is 58 dpt (looking at a distant
object).
1 -2
focal length = ------ = 1.72 10 m = 17.2 mm
58 dpt
The maximal diameter of the pupil is about 7 mm
=> 17.2 mm : 7 mm = 2.46
So, the maximum aperture given as "f-stop" is 2.5.
The minimal diameter of the pupil is in the range of 1.5 - 2 mm giving you
something around f/11 to f/8.6 as minimum aperture.
Looking at close objects the refractive power of the system inreases and
therfore, the focal length is decreased accordingly. This is the point
where I would really need my books because I don't remember the range of
accomodation. It is obvious that the minimal and maximal f-ratios are
somewhat lower in this case.
The main question that arrises now: What does it tell us?
The answer: I don't know...
cu
Philipp
--
Dr. Philipp Pagel
Cellular and Molecular Physiology
Yale University
From: lioninoil@aol.commoc.loa (Cornel Ormsby)
Newsgroups: sci.astro.amateur
Subject: Re: The eye as a camera: specs requested.
Date: 02 May 2000
IBM has a few informative pages about the human eye, beginning at:
http://www.pc.ibm.com/ww/healthycomputing/vdt13eye.html
++ Cornel Ormsby ++
From: pausch@saaf.se (Paul Schlyter)
Newsgroups: sci.astro.amateur
Subject: Re: The eye as a camera: specs requested.
Date: 2 May 2000
John Steinberg Nothanks@nospam.invalid wrote:
> Greetings:
>
> I'm looking for some kind of meaningful reference in comparing the
> average human eye to a camera lens. That is, what is the f-stop and
> focal length of the eye.
>
> I assume this is a dumb question, but what the heck, this seemed like
> the place to pose it.
Focal length approximately 23 mm
If the pupil is 7 mm large, this means an f-ratio of approximately f:3
Of course there are variations between different individuals, but
these are approximate figures.
Paul Schlyter, Swedish Amateur Astronomer's Society (SAAF)
Grev Turegatan 40, S-114 38 Stockholm, SWEDEN
e-mail: pausch at saaf dot se or paul.schlyter at ausys dot se
WWW: http://hotel04.ausys.se/pausch http://welcome.to/pausch
From: RM Mentock mentock@mindspring.com
Newsgroups: sci.astro.amateur
Subject: Re: The eye as a camera: specs requested.
Date: Wed, 03 May 2000
.....
Have you seen The Eye is a Minox site?
http://www.minoxlab.com/PZ051897/peterd.htm
--
RM Mentock
Ignorance? What's that?
http://sentient.home.mindspring.com/dan/
From: Martin Brown martin.brown@pandora.be
Newsgroups: sci.astro.amateur
Subject: Re: The eye as a camera: specs requested.
Date: Thu, 04 May 2000
Paul Anderson wrote:
> Interesting answers and good question. In comparison to a lens in the 35mm
> camera format, the eye is about 50mm. That's why 50mm is the "normal" lens,
> distorting in neither wide nor tele directions. Look through a 35mm camera
> with a 50mm lens attached and it looks similar to what you see without the
> camera to your eye.
That is only true for the 35mm film format. If you are taking 6x6 or half
plate images then a 50mm lens is a wide angle, and correspondingly used
onto a 10mm CCD chip it is a telephoto.
> The eye is not a "zoom" as one respondent claimed, but the f stop, or
> "speed" does vary. As we all know, the eye sees more after adjusting to the
> dark.
The guy was right. The eye solves the equation for focus 1/f = 1/u + 1/v
by varying it's curvature slightly. Focussed at infinity it's focal length
is ~ 25mm and focussed at closest accomodation of typically 200mm it is
about 10% shorter focal length of around 23mm.
Granted that is not much of a zoom, but it is none the less a change in
focal length.
Quite a lot of dark adaption is chemical in nature. The variation in the
iris alone is insufficient to account for the wide dynamic range of
lighting that the eye can tolerate.
The one thing he said which I disagree with is that the human eye is the
peak of optical performance. That distinction belongs to the raptors that
soar and hunt on the wing.
Regards,
Martin Brown
From: Martin Brown martin.brown@pandora.be
Newsgroups: sci.astro.amateur
Subject: Re: The eye as a camera: specs requested.
Date: Tue, 02 May 2000
John Steinberg wrote:
> I'm looking for some kind of meaningful reference in comparing the
> average human eye to a camera lens. That is, what is the f-stop and
> focal length of the eye.
Ballpark answer focal length 28mm.
Dark adapted iris 7mm diameter about f4 with resolution limited by
aberrations.
In daytime strong light 1mm diameter f30 and diffraction limited at
resolution 2' arc.
An optician can probably refine these estimates.
Regards,
Martin Brown
From Rollei Mailing List:
Date: Thu, 31 Aug 2000
From: Tan Anthony atan@addinc.com
Subject: RE: [Rollei] OT standard focal length
Working with several dimensional visualization software at work, I've
always wondered how a standard (human eye view equivalent) focal length is
assumed. We are constantly trying to merge computer models with real life
photographs. With the general relationship of focal lengths to film format
in mind, it seems that most people would agree that the 50mm focal length
of the typical 35mm film(24x36mm) with a vertical angle coverage of 27
degrees and horizontal angle coverage of about 40 degrees is standard. It
is obvious, based on the location of the human eyes, that our cone of
vision exceeds 100 degrees. Shouldn't we consider the 15mm(35mmfilm
format) with a horizontal angle coverage of 100 degrees be more in tune
with the way we see things? What do you think? The one thought that I have
is although the human cone of vision is large, we can only keep in sharp
focus within 40-60 degrees. The remaining cone of vision is used to
discern movement rather than visual cues.
tony
From Rollei Mailing List:
Date: Fri, 1 Sep 2000
From: bigler@ens2m.fr
Subject: Re: [Rollei] OT standard focal length
About the human eye :
It is very difficult to assign an equivalent "photographic" focal
lenght to the human eye, because the human eye has roughly two
different retina fields. The central field, the fovea, has a very fine
structure with an angular resolution of about 1 minute of arc i.e.
about 1/3000 radian. A good eye can distinguish a mesh of 1mm period
at a distance of 3 metres. In this regime the eye is in fact a
diffraction-limited lens. Unfortunalely this holds only for a few
degrees of field. But do not forget that the eye is constantly
scanning the angular field.
On the other hand the eye is sensitive to movement and color up to a
very wide angle not far from 180 degrees. So the eye is both a
telephote *and* a fisheye, but not with the same angular resolution.
If you look at some famous paintings, you can try to assign an
equivalent focal lenght to the picture, and you'll find a very wide
range of "focal lenghts". For example some famous paintings by Cezanne
showing the inside of his room are equivalent to a wide angle. Some
famous Dutch paintings like the "View of Delft" would be close to a
horizontal "panoramic" field of view. Traditional Chinese and Japanese
landscape images favor a wide angle vertical field ("portrait", not
"landscape" paper size...;-) But there are also many examples of
telephoto-like paintings (for example all conventional close-up
portraits of people), the artist having the ability to cencentrate on
a small filed of view simply because the eye allows to do this.
--
Emmanuel BIGLER
bigler@ens2m.fr
From Rollei Mailing List:
Date: Fri, 01 Sep 2000
From: Richard Knoppow dickburk@ix.netcom.com
Subject: RE: [Rollei] OT standard focal length
you wrote:
>Working with several dimensional visualization software at work, I've always
>wondered how a standard (human eye view equivalent) focal length is assumed.
>We are constantly trying to merge computer models with real life
>photographs. With the general relationship of focal lengths to film format
>in mind, it seems that most people would agree that the 50mm focal length of
>the typical 35mm film(24x36mm) with a vertical angle coverage of 27 degrees
>and horizontal angle coverage of about 40 degrees is standard. It is
>obvious, based on the location of the human eyes, that our cone of vision
>exceeds 100 degrees. Shouldn't we consider the 15mm(35mmfilm format) with a
>horizontal angle coverage of 100 degrees be more in tune with the way we see
>things? What do you think? The one thought that I have is although the human
>cone of vision is large, we can only keep in sharp focus within 40-60
>degrees. The remaining cone of vision is used to discern movement rather
>than visual cues.
>
>tony
I think its based on some assumptions which are not always true. The
idea is that a print at "normal" viewing distance will present an angle of
view and image sizes as would be seen by the eye if it had looked at the
scene. By angle of view is meant the perspective of the image rather than
the field of view. That is, its like looking through a window. The angle
is the same as if the window were not there but the field is much smaller.
The idea is that the angle of view of the camera is duplicated when a
print is viewed at a distance of approximately its diagonal. This is 53deg
regardless of the shape of the print. The "normal" focal length is equal
to the diagonal of the format. For 35mm full frame it is actually about
44mm rather than the more common 50mm. For 35mm cropped to 8x10 dimensions
it becomes about 42mm, which is why 35mm lenses are so popular, they are
actually closer to "normal" than 50mm.
Again, all this is based on assumptions about viewing distance, etc.,
which may not be valid in all cases.
It is interesting to look at photographs taken with very wide angle
lenses (but not fisheye lenses) which are large enough so that your eye
can be at the equivalent distance of the lens to film distance (focal
length times magnification). Viewed this way the "distortion" of the WA
lens disappears. You can also get the effect by looking at a small print
with a magnifying glass.
The human visual field is actually sort of football shaped (American
football), really not much wider than it is high. Panoramic formats fill
the visual field less than just a very large nearly square one. This is
one reason for the choice of a nearly square format for Eye Max rather
than a wide, narrow format like CinemaScope or Panavision. If you have
been to an Eyemax theater you know the very large image is nearly three
dimensional.
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com
From Rollei Mailing List:
Date: Fri, 1 Sep 2000
From: bigler@ens2m.fr
Subject: Re: [Rollei] OT eye resolution
> >The central field, the fovea, has a very fine
> >structure with an angular resolution of about 1 minute of arc i.e.
> >about 1/3000 radian. A good eye can distinguish a mesh of 1mm period
> >at a distance of 3 metres.
>
> 1mm at 9 feet? no way!
I know, this is amazing, but here is another experiment anybody can
do. The angular diameter of the moon is half a degree, i.e 30 minutes
of arc. How many "pixels" do you think you can see on the moon image
with the naked eye ? if I say : only about 30x30 pixels, you'll not
believe me either ;-);-)
--
Emmanuel BIGLER
bigler@ens2m.fr
From Rollei Mailing List:
Date: Sat, 02 Sep 2000
From: david morris davidrobertmorris@lineone.net
Subject: Re: [Rollei] OT standard focal length
You have the answer in the second half of your email. In the 1950's, I
think they settled on 45mm (35mm) as the nearest equivalent to the human
eye but this was shifted to 50mm with the introduction of SLR cameras
because of the need to have space behind the lens for the mirror box. I
have an 18mm Distagon for the SL35 (to keep ourselves on topic!) and when
enlarged up and cropped panarama style is seen in 45/50mm sections.
David Morris
Tan Anthony wrote:
> Working with several dimensional visualization software at work, I've always
> wondered how a standard (human eye view equivalent) focal length is assumed.
> We are constantly trying to merge computer models with real life
> photographs. With the general relationship of focal lengths to film format
> in mind, it seems that most people would agree that the 50mm focal length of
> the typical 35mm film(24x36mm) with a vertical angle coverage of 27 degrees
> and horizontal angle coverage of about 40 degrees is standard. It is
> obvious, based on the location of the human eyes, that our cone of vision
> exceeds 100 degrees. Shouldn't we consider the 15mm(35mmfilm format) with a
> horizontal angle coverage of 100 degrees be more in tune with the way we see
> things? What do you think? The one thought that I have is although the human
> cone of vision is large, we can only keep in sharp focus within 40-60
> degrees. The remaining cone of vision is used to discern movement rather
> than visual cues.
>
> tony
From Rollei Mailing List:
Date: Sat, 02 Sep 2000
From: Richard Knoppow dickburk@ix.netcom.com
Subject: Re: [Rollei] OT standard focal length
.....
>Pictures taken with the Rollei panorama accessory are interesting. The
>visual effect of a collage of these pictures is quite realistic. This
>suggests that a normal lens, panned across the visual field, is the
>equivalent of the eye's perspective.
>JMcFadden
The eye constantly scans. In fact, a completely still image prokected on
the retina will become invisible after a few seconds. This scanning is
what
inspired David Hockney to make his big collages. These paintings are
enormous. When you stand in front of one it fills your field of vision and
your eyes begin to scan it as though you were viewing an actual scene. By
the arrangement of the images in the collage Hockney directs your eyes to
scan what he wants. The effect is simply not brought out in reproductions.
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com
Date: Fri, 08 Sep 2000
From: Robert Long boblong@1st-uspride.net
To: rmonagha@mail.smu.edu
Subject: So-called fisheye lenses
Dear Robert,
While I'm delighted to have stumbled onto your Third Party Lenses page and
have bookmarked it for lots of enjoyable (and profitable) future
exploration, I must take up with you (or with a contributor to whom you
link? -- I can't now find the reference, but I think it was in the "Weird"
section) on the question of "distortion" in fisheye lenses.
There is a profound misunderstanding that colors much of what is written
about photography, particularly in the popular press. (Bert Keppler, with
whom I've worked, is a major contributor.) It often takes the form of
calling the human eye an "imperfect camera" because it fails radically in
terms of what photographers call "corner sharpness." If our retina were
capable of equal resolution everywhere, we would not have survived as a
species. In fact, the human eye works very differently from a camera and
for good reason.
Our depth-perception mechanism is much like the rangefinder in a Leica or
Contax: we rotate the two eyes until the images delivered by the foveae
(the tiny high-resolution areas near the center of the retina) "converge"
and, in effect, we "measure" the eye positions to judge distance -- and
movement toward or away from us. What would we not have been prey to
without this ability? But extend the high resolution to the entire retina
and we would be as confused about distance as were some of the prototype
designs for AF cameras. We could not have "triangulated."
Our way of seeing the world is far subtler and more complex than even the
most advanced cameras because of the intimate relationship between the
photomechanics of the eye and the enormous "data processing" capabilities
of the brain and its pattern-recognition systems. And it probably is
largely because these capabilities are applied unconsciously that we
photographers tend to give so little thought to the way we see and the
enormous differences between this process and those of photography.
Seeing is a four-dimensional process. Time is the absolutely
indispensable fourth dimension, in addition to the three of space.
Photos, by and large, are totally two-dimensional, and even conventional
"3D" images only simulate depth by the doubling of two-dimensional images.
In order to represent the human experience on a two-dimensional picture
plane (whether photographic or simply graphic) we must "throw away" half
the information supplied by the real-world experience. In technological
terms, we need a compression algorithm to reduce the information to only
that needed for recognition and reconstruction. In artistic terms, we
need a convention for telescoping our world onto the picture plane.
In conventional art, there are two rational, clearly defined, geometric
ways of doing this. Overwhelmingly, the most familiar and best understood
is what is generally called Renaissance perspective (though it was, in
fact, "revived" from extant examples from the Roman Empire and Hellenic
periods). It involves the assumption of a virtual fixed picture plane and
a rigidly fixed line of view. Lines from each point in the subject to the
virtual eye leave their image where they pass through the picture plane.
This is the kind of perspective rendering we expect from all non-fisheye
lenses and see every day of our lives in photos, on television, in the
movies, in magazines and books, in paintings -- in far more than 90% of
the graphic representations we are regaled with. If the public at large
is familiar with any one tenet of this form of perspective it is "straight
lines must always appear straight."
The only well defined alternative is "curvilinear perspective," in which
the line of view is not fixed. Instead, the image of each point in the
subject is rendered where the line of sight from the virtual eye would
pass through the virtual picture plane in looking directly at that point.
Straight lines whose images pass through the center of the picture plane
are rendered straight; others are not. So this sort of perspective is
much harder to draw precisely. As far as I'm aware, only one major
attempt has been made at its codification: Flocon & Barre's "Curvilinear
Perspective," published in French a half-century ago and quickly
translated into most other major European languages, though not into
English until 1987. Yet the technique was applied by some meticulous
draftsmen of the 19th Century and in relatively rough-shod form as far
back as the Middle Ages.
Now consider how we view the world. Since we can see only small areas in
full detail, we must scan the world around us. (A fixed line of sight
would net only one tiny patch of sharp vision, surrounded by the miasma of
peripheral vision.) We use no raster-like scanning system; traces of eye
movement in viewing pictures often resemble Brownian movement of the
subatomic world. The process is rather like downloading a RealAudio or
MP3 film clip: we hold the bits we have seen in memory and then "play
back" the entire, newly integrated object from our memory bank. We
remember straight lines as straight lines, so to this extent our
memory-pictures resemble those of Renaissance perspective. But the actual
process of acquiring the graphic information is comparable to curvilinear
perspective, because we must look directly at each point in the subject to
see its detail.
In that sense, the "fisheye" lens more closely represents the way graphic
information is gathered by the eye than does the conventional sort of
lens. The biggest difference between either sort of photographic lens and
the eye is that the lens can capture the full image instantaneously,
whereas the eye, working with the brain, can only build its images over
time, through scanning. We tend to be unaware of this because scanning
and recognition can happen incredibly fast, particularly with familiar
subject matter, but it remains a fundamental technological difference
between human vision and photography -- or any other graphic form.
There actually are three recognized standards of perspective rendering:
Renaissance, "standard fisheye," and Nikon's orthographic fisheye (I think
that's the term they used), but the last is of little representational
significance. Its formula was helpful in graphically calculating sky
illumination where the view of the sky is partially blocked, but its
images are anti-intuitive in most cases.
No matter; there is a formula for each of the three ways of rendering the
four-dimensional continuum of life in two-dimensional pictures. As long
as the resulting images conform to the appropriate formula, it cannot be
called distorted. Please save that word for those instances where the
image does not follow the formula. Distortion can "bend" straight lines
in conventional (Renaissance-perspective) lenses, which are supposed to
render them as straight, so that can legitimately be called distortion.
But as long as the curving convergence of lines in curvilinear perspective
conform to the intended formula, they not only are distortion-free but,
like it or not, are arguably imaged more nearly in the way our eyes would
image the same subject.
End of tirade.
I may take parts of my (still unfinished) book on this subject and put it
on a web page, since I have found no publisher to date. If I do, I'd be
delighted to have you link to it.
Bob Long
From Nikon mailing list:
Date: Sat, 18 Nov 2000
From: Alexander mediadyne@hol.gr
Subject: [NIKON] F of human eye
I learned today on the Contax list, that the human eye is rated at F2.1
Cat's eyes are at F0.9
Just thought it might interest some of you.
FRom Nikon Mailing List;
Date: Sun, 19 Nov 2000
From: "Mark Raymond" raymond@shore.intercom.net
Subject: [NIKON] Re: nikon-digest V2 #571, human eye
the average eye is 24mm with a range of 22 to 30mm being
common. functional
extremes of 17 to 36mm are relatively rare--these correspond to +10
diopters
of hyperopia to -30 diopters of myopia...allow some leeway here in the
last
numbers. the standard model eye assumes a length of 24mm and dioptic power
of 62D, 20 contributed by the lens and 42 by the cornea. anatomically, the
eye can have any permutation of length, corneal curvature and diameter and
lens shape...the pupil size as well as reacting to light also deminishes
greatly with age often down to a maximum of 3mm. a normal visual field
ranges from 60 degrees nasally to 90 degrees laterally for 150 degrees per
eye (equivalent to a 11mm camera lens with significant light fall off and
vignetting), 180 degrees binocularly...visual fields vary by facial
anatomy...ie. your nose, brow, maxilla and orbit may interfer.
there are many types of photoreceptors with different acquisition and
turnover rates and then they are also wired with different types of
neurons with variable abilities. i would guess the iso of cones is fairly
low and
rods moderately high. i'll have to look into that.
i prefer the social explanation though, my wife doesn't miss anything
either...like B&H; charges on the VISA!
enjoy,
MCR
From Contax Mailing List:
Date: Fri, 17 Nov 2000
From: Bob Shell bob@bobshell.com
Subject: [CONTAX] OT: Did you know?
Did you know that the human eye is F/2.1 ?
I just read this in the latest issue in an article about
icthyosaurs. Some of them had the largest eyes of any known
creature.
According to the same article a cat's eye is f/0.9.
Bob
From Contax Mailing List:
Date: Fri, 17 Nov 2000
From: Bob Shell bob@bobshell.com
Subject: Re: [CONTAX] OT: Did you know?
> From: Paul van Walree odobenus@xs4all.nl
> Reply-To: contax@photo.cis.to
> Date: Fri, 17 Nov 2000 15:08:19 +0100
> To: contax@photo.cis.to
> Subject: Re: [CONTAX] OT: Did you know?
>
> Bob Shell wrote:
>
>> Did you know that the human eye is F/2.1 ?
>
> In the dark or in broad daylight?
> Is the focal length F also known?
When the iris is wide open. The article does not say
but the focal length would have to be known to calculate
aperture. I remember reading it somewhere, and I think it
was around 20mm.
Bob
From Nikon Mailing List:
Date: Wed, 22 Nov 2000
From: Adam Pierzchala adam@pierzchala.newnet.co.uk
Subject: [NIKON] F of human eye
Tyler wrote: "I seem to recall while reading something about the Agfa
high speed film innovation that it takes (I really do not remember) 3-5
photons of light to hit the SAME grain/crystal before the film ever
records anything"
Well, I think your memory is spot on. When I used to work at Kodak, the
wisdom of the day was that 4 photons were needed to kick the grain into
action.
The flat T-grains which are like platelets ensure that a large surface
area is presented to light, so that there is a better chance of those
photons actually hitting their target. This is better than having a
narrow edge of the grain towards the lens.
I must admit though, that these grains are vastly larger than any
photon, in whatever uncertain state it happens to be, so why we need
acres of surface area is beyond me... :)
Regards, Adam
Date: Mon, 11 Dec 2000
From: Jerry Coffin jcoffin@taeus.com
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Question on 50 mm lens
nospam@ns.net says...
> I agree, I like the 50mm lens! Most equivalent to human vision at about 46
> degree angle of view,
This is a fallacy that's been repeated for many years by many
otherwise reputable sources, but it's essentially PURE nonsense.
Most people have a range of vision that extends to around 150-160
degrees horizontally and something like 90 degrees vertically (though
far more of that is downward than upward). As such, a panoramic
camera is MUCH closer to the angle of view of people's vision than a
50 mm lens can ever hope to provide.
That's a long ways from the whole story though, because vision is
extremely non-uniform. Lenses fall off to some degree at the edges
and corners, but eyes are MUCH worse in this respect -- the human eye
has (in essence) two major areas of sensitivity. There's a very
small area that has a high concentration of "cone" light receptors.
This provides high visual acuity and most color reception. Then
there's a much larger, roughly donut-shaped area that has relatively
few cones, but lots of "rod" light receptors. Rods are NOT sensitive
to color, but have a larger area so they're more sensitive overall.
The larger area also implies lower acuity.
Most people use the small area of cone receptors MOST of the time.
Purely subjectively, the angle of view provided by this area seems to
vary rather widely from one person to the next. I suspect this is
because the rod concentration doesn't immediately drop at the edge,
but falls off more or less gradually, so there's no exact "edge"
where you can say this area ends.
In any case, if you sit or stand still and simply concentrate on your
peripheral vision without moving your head or eyes, you'll quickly
find that the idea that you're restricted to seeing anywhere close to
the angle of view of a 50 mm lens is complete nonsense.
> and discrete 50mm lenses usually have lower f numbers
> and better low light performance than the cheap zooms. I have 2 Canon FD
> 50mm's, the newer 1:1.8, and an "old" FD 1:1.4 SSC, wonderful for low light
> photography. I also have a 28mm 1:2.8, and a 70-210mm 1:4.
There's little question that it's generally easiest to produce lenses
with focal lengths approximately equal to the largest dimension of
the area they're intended to cover.
Unfortunately, looking at the sorts of subjects of most people's
pictures, I'm forced to believe that a 50 is only rarely the ideal
choice. They're certainly cheap and high quality, but I consider the
angle of view troublesome at best.
If you're taking pictures of people, you usually want shorter for a
full-length shot or a group shot, but longer for a typical one- or
two-person head and shoulders portrait. If you shoot wildlife, you
almost inevitably want something considerably longer. A 50mm
sometimes happens to be about right for some scenery, but not
particularly often -- when it is best, it's mostly a matter of
accident; something like "well, we want to include that mountain over
there, and that stream over there, but NOT that power line just off
to the right", and it ends up that from where you're standing, a 50
works out to about the right framing. For most macro work, a longer
lens that gives greater working distance is normally a LOT easier to
deal with. A 50 (or 55 or whatever) macro works nicely for stamp and
coin collectors, but much less so for pictures of flowers, insects,
etc.
--
Later,
Jerry.
Date: 22 Jun 2001
From: bercov@sumo.als.lbl.gov (John Bercovitz)
Newsgroups: sci.optics,rec.collecting.coins,alt.collecting.stamps
Subject: Re: Comparing loupe magnifiers
There are two ways to quote the power of a magnifier because the eye can
be relaxed or accomodated. If the eye is relaxed, the power is 250/focal
length, but if it's accommodated to 250 mm, the power is 1 + 250/focal
length. Guess which formula almost all vendors use? ;-)
John B
--
John Bercovitz JHBercovitz@lbl.gov
Date: Sun, 05 Aug 2001
From: "Leonard Evens" len@math.northwestern.edu
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Depth of Field - 35mm vs MF
"Eugene A. Pallat" eapallat@apk.net wrote:
> Leonard Evens wrote:
>
>> One very important difference is the role played by the macula, which
>> is responsible for the great bulk of what you see. It is a relatively
>> small sensitive area in the retina. People who suffer from macula
>> degeneration have great trouble seeing in the normal sense.
> The macula is interesting compared to the rest of the retina where there
> are several rods and cones for every nerve cell. In the macula, it's
> one to one. If you see something with peripheral vision and need to see
> details, you *look* at it and the macula has much higher resolution.
> The down side, is that peripheral vision is is much more sensative to
> faint light. In astronomical observations, you can see fainter stars by
> *not* looking at it - you use averted vision. The tragedy with macular
> degeneration, is that the individual can no longer see details, and is
> funcionally blind. They're unable to read printed matter unless it's
> magnified very much. Gene Pallat
According to M. Pirenne, who wrote a famous book on painting, photography,
and vision, a few thousand cones in the macula do almost all the work in
normal vision.
--
Leonard Evens len@math.northwestern.edu
From: Tony Polson tony.polson@btinternet.com>
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Naturalism/ was: Depth of Field - 35mm vs MF
Date: Fri, 03 Aug 2001
Phil Stripling phil_stripling@cieux.zzn.com> wrote:
> I read somewhere years ago that the 135mm lens (in 35mm cameras) was 135mm
> because it represented what the human eye saw when it was focused on a
> particular object. (Not that the eye zooms in, but that it focuses on
> something to the exclusion of other things in a way similar to the 135mm
> lens.)
Hi Phil,
A survey on this precise same topic was conducted by a UK magazine over
20 years ago. The conclusion drawn was that most people questioned by
the magazine felt the focal length which gave a field of view and
perspective similar to that of the human eye was ...
... around 70mm.
--
Best regards,
Tony Polson
From: HypoBob hypobob@pacbell.net>
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Depth of Field - 35mm vs MF
Date: Sat, 04 Aug 2001
The incredible selectivity of the human eye was demonstrated to me by a physics professor years
ago. On the chalkboard he drew two dots, less than an inch apart, and asked us to look at one
and then the other. Even people at the back of the lecture hall, 30 or 40 feet away, could feel
their eyes shift focus as they moved their attention through that extremely small angle from one
dot to the other.
It's an amazing organ,
Bob
------------------------
Leonard Evens wrote:
> "Mark
> Anderson" andermar@teleport.com> wrote:
>
> > Stephe ms_stephe@hotmail.com> wrote:
> >> Leonard Evens wrote:
> >
> >> > You can see some things with peripheral vision, and I believe you can
> >> > train yourself to make better use of it. But I don't believe you
> >> > can see small detail with peripheral vision no matter what you do.
> >
> > The macula has better detail vision for two basic reasons. First,
> > there's a high concentration of cone cells there, and cones are
> > responsible for color vision, (but they're less sensitive to light).
> > Also, there aren't blood vessels overlying it. (That's why it's a pit,
> > a dip, on the surface of the retina.)
>
> Also, the cones in the macula go individually through neurons to the brain,
> while the rods in the rest of the retina share neurons. Moreover, the
> section of the brain devoted to the macula is larger than that devoted to
> the rest of the retina. From the brain's point of view, the macula is
> larger despite its small physical size.
>
> > The rest of the retina, OTOH, has
> > blood vessels over it, since the vessels come out from the optic nerve
> > area, course over the retina, and then penetrate. (IOW, it's made
> > ass-backwards). The rest of the retina has bunches of rods, however,
> > that are more light sensitive, but deal in monochrome. A good use of
> > peripheral/averted vision is what visual astronomers do. They look aside
> > from their area of interest, and dim nebula show up that disappear if
> > looked directly at.
> >
> >> No it's isn't "normal" but again most people never bother to even try
> >> to use any of this part of their vision.
> > You can easily demonstrate that anyone regularly uses their peripheral
> > vision to pick up movement.
> >
>
> The importance of the macula was brought strongly to my attention when I
> experienced a bout of macular edema following cataract surgery.
> Fortunately it was temporary, but during the month I had it, I had great
> difficulty using that eye despite the fact that only a very small region
> in the center of vision was affected. I could see that just outside
> that region things were clear, but I couldn't shift my vision to look
> there. I couldn't read normal sized type. I got some idea of what
> people with macular degeneration go through. It isn't fun.
> --
>
> Leonard Evens len@math.northwestern.edu 847-491-5537
> Dept. of Mathematics, Northwestern Univ., Evanston, IL 60208
From: jr@redmink.demon.co.uk (John R Ramsden)
Newsgroups: sci.math,sci.optics,sci.physics
Subject: Re: Human "refresh rate"?
Date: Tue, 27 Mar 2001
F=m.dv/dt agutrg@hotmail.com wrote:
>
> A monitor has a refresh rate - everyone must know what refresh rate is,
> I assume. The faster the refresh rate the more "smoother" the movements
> appear on the screen.
>
> I was just wondering, what is the refresh rate of the human eye/brain? Is
> the "refresh rate" limited by the properties of light? or by our senses?
> (surely refresh rate can't be infinite!)
I believe the effective refresh rate of the human eye/brain is somewhere
around 16 frames per second. (At its fastest a human brain wave travels
at the same speed as a heavily-laden donkey toiling up a mountain path!)
The refresh rate of animals differs widely; for example that of certain
flying insects such as bees is over two hundred frames per second.
There are also differences in other optical attributes such as colour
reception and focus field. For example cats and dogs have only two colour
receptors, as opposed to humans' three and birds' five, and large cats
such as lions have a horizontal linear focus area, suitable for scanning
horizons for prey, in contrast to that of most animals, including humans,
which is a point focus.
On this topic, I wonder how film makers produce the slightly bizarre
surrealistic "disjointed" visual effects in the action sequences of
recent films such as Saving Private Ryan and Gladiator. They appear
to be speeded up sequences, with frames omitted to lend a slightly
stroboscopic effect.
cc: sci.optics and (God help me ;-) sci.physics
Cheers
John R Ramsden (jr@redmink.demon.co.uk)
From: Stefan Patric tootek2@yahoo.com
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Focal length equivalent to normal eye?
Date: Sun, 3 Mar 2002
Mxsmanic wrote:
> "Stefan Patric" tootek2@yahoo.com wrote
>
>> ... and the lens of the human eye changes its
>> focal length instead of the distance from the
>> retina to focus.
>
> Neither of these changes. The shape of the lens changes to modify the
> focus distance of the eye. If focal length changed, the size of the
> image in your field of vision would change as well.
Wrong. When you change the shape of any lens, you change its focal
length. That's physics.
There are only two basic ways to focus images with a simple lens, which
is what the lens of the eye is. One, if the focal length of the lens
is constant, you must change the lens to film distance; and, two, if
the lens to film distance is constant, you must change the focal length
of the lens. Cameras use the first and the eye uses the latter. This
is the only way the eye has to focus: by changing the shape, and,
therefore, its focal length.
Now as to: changing focal length changes image size. I suspect your
conclusion is drawn from your experience with camera lenses, i.e. the
image in the viewfinder is twice as big with a 100mm lens on the camera
than with a 50. They are designed to work that way. The lens of the
eye is not. With the eye, image size is a function of lens to subject
distance. Near object are rendered larger than that same object far
away.
Try focusing sharply on a near object, and, then, without changing your
position focus to infinity. Did the image of the near object change
size? The lens of your eye modified its shape and focal length to
change focus, but the image sizes of all the objects in your field of
vision didn't change size with that change.
I suggest you take a look at some basic texts on optics about simple
and compound lenses, and how they work.
--
Stefan Patric
tootek2@yahoo.com
Date: Fri, 8 Mar 2002
From: "Gerald W. Crum" gwcrum@apk.net
To: Robert Monaghan rmonagha@post.cis.smu.edu
Subject: Re: Lens Kits
Bob,
Thanks for the reply. I understand your point about the 35 or 50 as the
"normal" lens. I have two comments on "normal".
The first was from a local shopkeeper when I was buying an SLR back in the
70's. He showed me both a 40 mm on a Pentax and a Konica, and a 35 f/2.5 E
lens on the Nikon. I told him I preferred the view of the 50 mm. He said,
"Maybe for now, but one day you'll be using a 35 or 40." How prophetic!
What turned me was the realization that many scenes I saw where I thought,
"Boy, that would make a great shot", framed perfectly in the 40 mm Pentax.
The second part of this, is that after I had this inspiration of a great
shot a number of times, I sat down one day and tried to figure out just how
my eyes and brain worked versus focal length. I spent an entire day out on
the back porch with my camera, lenses, pad and pencil, a steel tape, and a
scientific calculator. By mid-afternoon I had it figured out. And this is
what I found:
1) the standard tables of lens angle of view give the angle on the diagonal.
We don't see that way. Our eyes are on a horizontal plane, and our field of
view is wider than it is high. So we need to worry primarily about the
horizontal angle of view for the particular format we are looking at. This
is all 35 mm for me. Comment that 43 mm is the diagonal of the 35 mm frame
and therefore is the focal length of a "normal" lens seems to be more of an
argument for Pythagoras, rather than relating to how we view scenes and
prints.
2) I found that if the eyes are not converged, but focused at infinity, the
effective angle of view corresponds to roughly a 38 mm lens. So a 35 or 40
mm sees about the same way we do when we are not focusing in on a specific
detail. I know our peripheral vision extends to nearly 180 degrees, but
color perception and sharpness are best in the areas I am talking about
here. It also takes a while to learn to be aware of when your eyes are
converging or not. I refer to this region as the focal length of perfect
composition. Or the region of sudden inspiration, since when we glance at a
distant scene we have not yet converged our eyes to pick out details, but
are taking in the whole scene.
3) If you close one eye and run the same experiment, the region of sharpest
vision is that of a 50 mm lens. I refer to this as the focal length of
perfect perspective. Great for art works and architecture if we want to
preserve the proportions. But jarring for portraits. An artist I know (she
teaches photography and art at Case) uses a 55 mm lens for portraits.
People who see her work comment on the tension in her prints. There is
always a feeling of confined energy. I think we are sensing the wrongness
the one-eyed view point her lens gives.
4) I then worked on the issue of convergence of the eyes. This was quite
surprising as I found that there is a minimum angle of convergence which is
stable. If you try to converge less than that, your eyes tend to flicker.
I believe this is a matter of the minimum amount of muscle tension which is
required to stabilize the eye position. This turned out to be about 80-85
mm. Anything narrower is stable as you concentrate your attention on a
point. So I think of 85 mm as the beginning of the region of convergent
vision, or the region of detail.
5) if you take all the previous points, you can define your vision in terms
of focal lengths. 35-40 mm is the point for non-converged binocular vision.
50 mm is a singular point of monocular vision. 85 mm and longer is the
region of stable convergence. Shorter than 35 mm is the region of wider
than normal vision. It requires motion of the head or eyes to get the same
effect.
6) Since 35 mm is the equivalent of non converged eyes, and 85 is the
minimum convergence, there is no vision mode between those two focal
lengths, except the singular point at 50 mm. If a zoom lens covers 35-70,
you will always want more length, but not often a lot more width. A 35-105
or 35 -135 covers the critical 35 mm focal length and gives a useful amount
of length beyond the 85 mm point. Hence my satisfaction with the 35 and
70-150 combo.
Once you understand what the various focal length ranges correspond to, it
helps you to pick out your lens set.
After I had gone through all this effort, I thought I can't be the first
person to have found this. So I went to the library and began to search for
prior articles. Sure enough. In the Kodak Photographic Encyclopedia I
found references to all of the things I have listed. I feel pretty good
about working it all out for myself, even though I had rediscovered the
wheel. But why is this not common knowledge?
Any thoughts or comments?
Best Regards,
Jerry
----- Original Message -----
From: "Robert Monaghan" rmonagha@post.cis.smu.edu
To: "Gerald W. Crum" gwcrum@apk.net
Sent: Friday, March 08, 2002
Subject: Re: Lens Kits
> Hi Jerry,
>
> Some good points, I find I've grown used to the "normal" lens view since
> I have so many medium format cameras (TLRs..) where that is what you get
;-)
>
> but see http://medfmt.8k.com/third/kits.html camera lens kit
> selection pages, for related notes and observations.
>
> As you noted, it basically turns on if you prefer the 35mm or 50mm as a
> normal lens, from there, your lens choices and steps and which
> teleconverter to use fall into place ;-) If you pick the "wrong" TC, you
> only get one additional lens focal length in your kit ;-) etc.
>
> thanks for sharing your notes! - I'll add them to the new site's updated
> pages at http://medfmt.8k.com/third/kits.html
>
> regards bobm
From: "Mxsmanic" mxsmanic@hotmail.com
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: DOF "overrated"?
Date: Sun, 17 Mar 2002
"Leonard Evens" len@math.northwestern.edu wrote ...
> Does that mean that myopes with corrected vision
> could in principle have higher accuity than people
> with normal vision? There must be something
> wrong with this reasoning, but off hand I don't
> see what.
It seems sound.
The Guiness Book of World Records used to list (and perhaps still does)
Veronica Seider, a German dentist, as having visual acuity 20 times
better than normal; she could identify people up to a mile away. I
thought about this on many occasions, because there simply is no way to
obtain that level of acuity with normal eyes--it would require resolving
details that are much smaller than a single cone cell. However, it
occurred to me also that she might simply have slightly anomalous
optical properties to her eyes--they might have a longer focal length,
effectively magnifying images and producing details that are twenty
times normal size, thus allowing her to see twenty times better. Her
visual field overall would be reduced in angular area in consequence,
but she wouldn't necessarily notice that, and if nobody tested it,
nobody else might notice, either. It would explain her "impossibly"
good vision, since no normal eyes could manage that. Essentially she'd
be trading angle of view for resolution of small details. As for how
she'd get the long focal length, I don't know. A difference in the
shape of the cornea (the major refractive element in the eye), perhaps.
A non-spherical eye seems unlikely (too much mechanical stress), but who
knows?
From: "Duncan Murray" duncan.duncan@btinternet.com
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Why is MF nikkor 50mm 1.8 so cheap?
Date: Sun, 14 Apr 2002
This thing about the Pentax 43mm f1.9 having a three-dimensional property is
really getting on my nerves. As far as I know it was Pentax's all-out
effort at creating the best (sharpest, least distortion, max contrast, nice
bokeh, etc etc etc) standard lens. However, looking at photodo's website, I
was really surprised to see it have such a low rating. The 43mm was chosen
to mimic the exact same proportions (not perspective) of the human eye, so
would that be to do with the 3d effect? However, I clicked on the MTF
graph, and if you look carefully, you can see why these average MTF's can be
very misleading, favouring the planar lens rather than one that has a curved
field of focus. Looking at the graph, on the far left, you can see the
amazingly high MTF value at the centre of the frame, this is even higher
than the other lens I was comparing it with (50mm FA, 4.6(!)). Then the
curve smoothly runs down (unlike many lens that represent a mountain-range)
to the bottom right. Obviously Pentax were going the whole hog in mimicing
the eye, and were even giving the lens the curved focus fields that our eyes
have. I really wander what the average MTF of this lens is when focused on
a curved screen, rather than a planar one they did the tests on.
Duncan.
....
from leica topica mailing list:
Date: Mon, 7 Jan 2002
From: david rose jennysup@yahoo.com
Subject: RE: Left-brained Microbiologist
Mervin,
I tried this and it blew me away! I thought everyone was kidding!
I used my Voigt with left eye because it was much more comfortable, but
got tired of my nose print on the back of the camera. When I got my M6
I decided to justs witch to the right eye from the get go. It took me
about a week to feel comfortable doing so.
Am I losing something using my right eye even though my left is
"dominant"?
Wow, learn something new every day. This is wild
regards
david
David Rose
Mervin Stewart wrote:
> Make a circle with your thumb and index finger of either hand, hold your
> finger circle at arms length and view some object through it with both eyes
> open. Center the object in the circle. Close your left eye..if the object
> remains in the center of the circle you are right eyed. If on the other hand
> when you close your right eye and the object is still centered you are left
> eyed....If you are left eyed and right handed, that means either that you
> have crossed dominance or that someone changed your natural handedness early
> on...
> I am a lefty, but someone thought in first grade I should write right handed...
> So I do and can actually write with either tho I am better with the right.
> Let me know what you discover with the test.
> Mervin
From contax mailing list:
From: "Austin Franklin" darkroom@ix.netcom.com
Subject: RE: [Contax] Digital Vs 400 asa film
Date: Wed, 7 Aug 2002
> Alan wrote:
> >...
> >The human eye can, without dark adaption, detect a contrast
> ratio of about
> >100 to 1.
> >...
>
> I have seen this number quoted in several places, but I think it is more
> like 1000:1.
Hi Joe,
It is only 100:1 for any given light. When the light changes, it's 100:1
again, but over a different range.
So, just like film, can hold a range of X, it depends on where you set your
shadow point at, or your highlight point at...and you can move those up or
down...but you still only get X stops.
So, it's still only 100:1 for the eye ;-)
Regards,
Austin
From contax mailing list:
From: "Austin Franklin" darkroom@ix.netcom.com
Subject: RE: [Contax] Digital Vs 400 asa film
Date: Wed, 7 Aug 2002
...
Joe,
You're talking color...the human eye can discern 16M colors, but only 100
graytones. If I did post the references here, please check them out, if I
didn't, I'd be happy to post them.
Print out a 64 and a 128 graytone step wedge, and see if you can discern all
the adjacent tones.
Austin
Date: Wed, 14 Aug 2002
From: "Mxsmanic" mxsmanic@hotmail.com
Newsgroups: rec.photo.digital,rec.photo.film+labs,rec.photo.equipment.35mm
Subject: Re: Input specifications for Fuji Frontier digital minilabs?
"Bit Bucket" bitbucket3@earthlink.net a Tcrit
> Whoa there, Pilgram. I don't think so. "The retina
> contains two types of photoreceptors, rods and cones.
> The rods are more numerous, some 120 million, and are
> more sensitive than the cones. However, THEY ARE NOT
> SENSITIVE TO COLOR." --
Such are the dangers of a quick glance at the Web.
The retina contains two major types of photoreceptors, rods and cones (named
after their approximate shapes under a microscope). Rods are extremely
photosensitive but they all contain the same pigment and they all have the
same spectral response, which peaks in the blue-green end of the spectrum.
In contrast, cones come in three varieties, each of which has a different
pigment: red-sensitive, green-sensitive, and blue-sensitive. Color vision
depends on processing of separate red, green, and blue signals from the
three types of cones. Green cones are much more numerous than blue or red
cones; blue cones are the most rare. The center of the visual field on the
retina contains only cones; as one moves towards the periphery, the cones
diminish in number and density and rods become more prominent.
This physiology of cone cells in the retina is the basis for the
trichromatic display and printing systems universally used to create images
for human viewing.
> However, since CCD sensors are not sensitive to
> color (like our rods), there are no "missing components"
> in the luminance readings ...
CCDs are covered by colored matrix filters in digital cameras. These
filters place a color filter over each pixel of the CCD; the usual colors
are red, green, and blue, with green filters being more numerous than blue
or red filters (to mimic the physiology of cone cells in the eye). Thus,
CCD sensors are indeed sensitive to color, even if the underlying CCD has a
constant spectral response without the filter.
> They are masked by filters of KNOWN DENSITIES and
> KNOWN COLORS, which would not seem to require any
> interpolation whatsoever to adjust the readings
> accordingly for black and white luminance.
Black and white luminance are a function of several colors, not just one.
You need red, green, and blue information to perceive luminance--because
that's how the human eye does it. This being so, no pixel that receives
only one of these three colors can provide enough information for accurate
luminance; and since all single-CCD cameras have information for only one
color for each pixel, interpolation is necessary to derive luminance. The
luminance signal is somewhat more accurate than the chrominance signal, but
it is not 100% accurate, because of the interpolation.
Date: Sat, 17 Aug 2002
From: "Mxsmanic" mxsmanic@hotmail.com
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Megapixels vs Medium Format question
"Thom" asfl@freemail.com.au a Tcrit
> The average human being can only see about
> 58,000 colors! Having a pallet with 16M
> is a waste of resources.
Not so. Typical human vision can distinguish about 16 million separate
colors. 64K displays often show visible posterization in gentle gradients,
especially in blue.
From: "Ralph W. Lambrecht" RalphLambrecht@t-online.de
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Focusing and Depth of Field concerns
Date: Wed, 28 Aug 2002
Henry Dreyfuss conducted a study for the US Army in the 1960s and determined
that the minimum separable visual angle is about 1 minute of arc or 0.017
degrees. However, he stated that some eyes are twice as good. The study also
shows that the result is largely influenced by the lighting condition and
contrast. Two bright stars against a dark sky, for example, can be separated
down to 0.05 seconds of arc or an impressive 0.000014 degrees.
Using this data for photography, most Depth of Field tables assume a viewing
angle of 2 minutes of arc. Example CoC = 0.022mm for 35mm film. Half that
diameter would be more realistic for critical consumers. Here are some examples
of critical CoC for common film formats.
24x36 0.011
6x4.5 0.020
6x6 0.021
6x7 0.024
6x9 0.026
4x5 0.044
5x7 0.056
8x10 0.089
11x14 0.126
These values assume an uncropped print viewed from a distance equal or larger
than the diagonal of the print. For more information see:
'The Measure of Man'
Y 1967 by Henry Dreyfuss
and
'On the Psychophysical Function'
Y 1975 by H. L. Resnikoff
Ralph W. Lambrecht
"Q.G. de Bakker" wrote:
> Leonard Evens wrote:
>
> > You offer very good advice, but let me quibble a bit.
> >
> > The old rule of thumb was that the largest disc that the eye can't
> > distinguish from a point at 10 inches is 0.01 inches or about 0.25 mm,
> > which comes out to 4 lp/mm, using your formula. Certainly some people
> > can see better than that, perhaps being able to see as well as the
> > equivalent of 8 lp/mm, as you say.
>
> Let me quibble a bit too.
> If the largest disc that the eye can't distinguish from a point is (about)
> 0.25 mm, you would get 4 of them (single (!) points; stretch them in one
> direction and you will have lines) in a mm. That are only 2 pairs (2 lp/mm),
> not 4.
> No? ;-)
From: Uncle Al UncleAl0@hate.spam.net
Newsgroups: sci.optics,sci.physics
Subject: Re: Fluorescent optics
Date: Mon, 26 Aug 2002
Bruce Bowen wrote:
>
> Would it be possible for people to see into UV with fluorescent
> optics? For example contact lenses, eyeglasses, etc. I believe the
> material would have to fluoresce somewhat coherently with the incoming
> UV, and not just scatter randomly in order to be able to image
> effectively.
The natural lens oin your eye is a potent UV absorber. Young lenses
cut off at 400 nm. By middle age the lens is distinctly yellow, then
it shades to brown. Middle-aged folks confuse black and blue socks
and shoes, especially under incandescent light. Old farts without
cataract extractions dress in weird bright colors. Old ladies'
makeup, if they retain OEM lenses, looks like clown school homework.
Without the lens you can see to at least 380 nm or so, past
blacklight. UV eats your retina.
If you want to look into the UV or NIR, use a camera.
--
Uncle Al
http://www.mazepath.com/uncleal/
From: Uncle Al UncleAl0@hate.spam.net
Newsgroups: sci.optics,sci.physics
Subject: Re: Fluorescent optics
Date: Tue, 27 Aug 2002
Ian Stirling wrote:
>
> In sci.optics Uncle Al UncleAl0@hate.spam.net wrote:
> {snip}
> > The natural lens oin your eye is a potent UV absorber. Young lenses
> > cut off at 400 nm. By middle age the lens is distinctly yellow, then
> > it shades to brown. Middle-aged folks confuse black and blue socks
>
> Do you know what drives this aging?
> Is it UV?
It's Maillard browning, the same thing that makes for tasty bread
crusts - pendant amino groups from lysine residues plus reducing
sugars give Schiff bases, then further condensation. There is no
discrete knowlege of the process and no trustworthy countermeasures
either as prevention or treatment. Diabetics have big problems with
their eyes' lenses.
--
Uncle Al
http://www.mazepath.com/uncleal/
From: jon@messuage.demon.co.uk (Jonathon)
Newsgroups: sci.optics,sci.physics
Subject: Re: Fluorescent optics
Date: 27 Aug 2002
brucebo@my-deja.com (Bruce Bowen) wrote...
> Would it be possible for people to see into UV with fluorescent
> optics? For example contact lenses, eyeglasses, etc. I believe the
> material would have to fluoresce somewhat coherently with the incoming
> UV, and not just scatter randomly in order to be able to image
> effectively.
>
> -Bruce bbowen@pppppppppppacbell.net
Many years ago I knew someone who had a replacement lens in one eye.
This was obviously luminescent, and he could 'sense' UV. He couldn't
see an image, but was aware of the glow.
I guess/hope modern lenses aren't luminescent.
Jon
From: jge@cs.unc.edu (John Eyles)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Megapixels vs Medium Format question
Date: 29 Aug 2002
Since we're talking optometrics, I have a conundrum. I realized
I'm probably not focusing my Fuji range-finder very accurately,
because I'm so presbyopic myself. Fortunately it takes Nikon
diopters (the FM2/FE2 size), but I can't figure out which to
get. An eye doctor measured me and said I need something between
+1 and +2 for my reading glasses, but said WHICH I need depends
upon how far I sit from my computer screen etc.
So which should I get for my camera diopter ? I suppose it depends
on where the un-dioptered viewfinder puts the virtual image. I guess
I COULD buy several (at $17 a pop) and try to return the unused ones
(or save til my eyes get even worse). But given how hard it's been
to get B&H; to credit for returned merch ... (ok, they claim they're
just busy).
Thoughts ?
Thanks, John
From: brianc1959@aol.com (brian)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Medium Format vs. 35mm
Date: 7 Sep 2002
"Mxsmanic" mxsmanic@hotmail.com wrote
> "Jeff Haddock" liftwithyourknees@yahoo.com a Tcrit
>
>
> Depth of field exists only
> because human eyes cannot see with infinite resolution; if they could, then
> only the plane of focus would be sharp in an image--there would be no depth
> of field at all. Since DOF is a function of the eyes, then, it follows that
> the more closely you examine an image, the shallower the DOF will appear to
> be. And, since you can enlarge MF a lot more than 35mm without being
> limited by film grain, you can examine MF prints a lot more closely, and so
> the DOF upon the closest possible examination will be much more limited.
You're ignoring the wave nature of light here. There is a thing in
optics called the diffraction-limited depth of field. In image space
it is approximately equal to the f/#^2 measured in microns for visible
light. Thus, if you shoot at f/10, the diffraction-limited depth of
field will be about 100 microns at the film plane. Within the
diffraction-limited depth of field envelope it is essentially
impossible to determine a unique plane of sharpest focus. Needless to
say, this is a much higher standard than the typical circle of
confusion calculations based on print sizes.
Brian
from minolta mailing list:
Date: Wed, 25 Sep 2002
From: "haefr2000" ray_h71@hotmail.com
Subject: Amazing Facts
Lost in all our discussions about current digital camera pixel
density and proposed pixel density is that it was all done before.
Consider, if you will, one of the most amazing analogs in nature:
OUR OWN RETINAS! The entire retina (conveniently spherically shaped
to negate spherical aberrations from our optical system, no less!)
has approximately 1 million nerve endings - implying 1 million
pixels. This, in itself is not all that impressive when compared
with 6.3 megapixels in Canon's sensor array on the D-60. But, and
here's the kicker, MOST of the retina except for the macula is used
for peripheral vision. the "sensors" - "rods" in this case, are
color perception insensitive, but they are great for getting us out
of trouble at night from critters that would be willing to indulge us
as a late night snack in case we were caught unawares (great for low
light motion detection). Now, the macula, specifically a tiny area
of the macula, the foveal pit, is truly a wonder. For dimension
freaks the macula is approximately 3mm in diameter*. The foveal pit
is approximately 1/10 as large at 0.3mm in diameter* - roughly the
area of a pinhead (not the pointy end). This tiny area is populated
exclusively by "cones" - the "sensors" responsible for our most acute
resolution and color perception. It's what we lay the image on when
we "look" at something critically. With that 0.3mm diameter, the
area works out to less than 0.08 square millimeters ([pi x
0.3mm^2]/4) but still contains more than 250,000 "cones"* (each one
representing a pixel). Still not impressed? To put the significance
of this in perspective, at that packing density, a 6 megapixel sensor
array would have an area of just under 2 square millimeters ([6 x
0.08mm^2]/0.25])! Or expressed another way, a standard 35mm frame
measuring 24x36mm would contain over 2.5 gigapixels ([[24mm x
36mm]/2mm^2] x 6)! Put THAT in your DSLR designed for conventional
35mm format lenses! The really amazing thing is that we can walk,
talk, scratch an itch, (ahem, Kent, even calculate 1/2 f:stops) and
check out pretty young thangs simultaneously with all the data we're
constantly processing!
*The data I presented was extracted and calculated from information
in Stuart Duke-Elder's second volume of his "System of Ophthalmology"
ophthalmology residency text.
From: "Bob May" bobmay@nethere.com
Newsgroups: sci.optics
Subject: Re: Yellow tinted lenses
Date: Sat, 5 Oct 2002
The theory is that looking at the yellow part of the spectrum is going to
decrease the "poor focusing" blue and red rays, the blue end of the spectrum
being the light most diffused by the droplets of water. While this is
indeed true to a degree, the glasses aren't used in the high moisture
conditions that can be helped in this matter but rather in an attempt to
provide a "better" set of sunglasses.
One of the things that the glasses actually make worse is the color
reception of the eyes as the eyes are self-balancing for color (stay in a
particular room with specific lighting and all the colors look natural in a
few minutes) so they tend to overcorrect for the blue and red end of the
spectrum, causing the yellow filters to pretty much stop working. The
self-correcting nature of the eye tends to hid the fact that the yellow
filters only work for a minute or so before the eye has rebalanced its
sensitivity to the incoming light and thus negate the results of the
filters. When the filters are taken off, the overcorrection makes the scene
overblue and red and thus you really think that the yellow filters work all
the time.
A yellow filter on a rifle scope will work well as the eye doesn't become
accomadated to the yellow tint in the time required to aquire a target and
hit it for the obvious reasons described above.
Also, neutral tinted filter lenses will assist in reducing the excess light
coming in and open the irises a bit so that the apertures will provide a
better resolution to the image on the retina of the eye. Opening the iris
too far tho ends up looking through the edges of the eyelens and that is the
poor part of the lens and thus you end up with poor vision for another
reason.
Hope this helps.
--
Bob May
From: "Kevin Neilson" kevin_neilson@removethistextattbi.com
Newsgroups: alt.photography
Subject: Re: What is the human eyes' ISO equivalent?
Date: Wed, 16 Oct 2002
The process of eye evolution is well-documented and really not that amazing,
but I've found there's little value in discussing such things with
non-Darwinists.
The human eye has some really poor design elements to it. The first is the
fact that a large proportion of people have screwed-up focal lengths,
requiring them to wear corrective lenses. (If God did indeed design the
eye, he did it poorly.) Because of the way the eye evolved, the optical
nerve creates a blind spot right in the middle of the retina. For the same
reason, the nerve layer is on top of the retinal cells requiring light to
get attenuated passing through this upper layer. Squid, which have eyes
that evolved convergently, don't have these problems. The resolution isn't
that great in most of the eye, which is why the fovea, the high-resolution
part in the middle, evolved later. It's like an aftermarket add-on. The
lens muscle is weak and wears out after 40 years, and the cornea gets all
hard a few decades after that.
The retinal cells are pretty slow, but they do have very good dynamic range.
A lot of the slowess is overcome with the ability to track well. The eye
has built-in motion detection circuitry and thus can track items very well,
allowing them to stay focused on the fovea and to let the light from dim,
moving objects accumulate. Like an IS lens.
-Kevin
...
From rangefinder mailing list:
Date: Wed, 23 Oct 2002
From: "Bob Sheppard" projfin@bellsouth.net
Subject: Re: [RF List] Age: RF vs SLR
Similar question. I remember reading in a discussion of fast lenses that an
f-stop of 1.0 approximates the vision of the human eye.
----- Original Message -----
From: "Jim Williams" jimwilliams1@cox.net
To: rflist@topica.com
Sent: Wednesday, October 23, 2002
Subject: Re: [RF List] Age: RF vs SLR
> Dante Stella wrote:
>
> > The interesting thing is that SLR finders, especially the pre-AF ones,
> > can
> > be brighter than life once the lens hits f/1.4 or faster. F/2 is
> > equivalent to the light the human eye sees.
>
> Just out of curiosity, what's the basis for this assertion? I realize
> that the lens in the eye has a (variable) focal length and a maximum
> aperture (which probably varies in size from person to person, although
> possibly not all that much) but the process of 'seeing' is considerably
> different between the eye and a piece of film. I recall reading (I
> believe in 'Q.E.D.', by Richard Feynman) that if you're young, healthy,
> and give your eyes plenty of time to adapt to darkness, they can detect
> bursts of light amounting to as little as eight individual photons. I
> don't know how one would go about relating that figure to the amount of
> light a lens 'sees', but I would guess that a piece of film would have
> to accumulate light over an exposure of several seconds to register
> that amount of illumination.
>
> What that translates into is that I don't think a lens with a larger
> numerical aperture would act as a 'funnel' to make the scene appear
> brighter than you'd see it with your bare eyeball. If it would, the
> Army could save all that money it spends on those electronic
> night-vision systems and just fit the soldiers with great big
> eyeglasses, right?
>
> > Assuming that there is a
> > 1-stop loss in the finder system (that would actually be huge), it
> > should
> > be easier to focus SLRs in low light with f/1.4 lenses and faster.
>
> Another factoid dredged out of my sometimes dubious memory: seems as if
> I recall (in one of Norman Goldberg's technical articles in the old,
> more-technical 'Pop Photo') that because the condenser in an SLR
> viewing system limits the illumination angle on the focusing screen to
> the central portion of the lens' exit pupil, you're always focusing
> through an effective aperture no greater than about f/2.8, no matter
> how fast the lens you mount on the camera. This was noted in answering
> a reader's question about why some pictures he had taken with a long,
> fast tele lens at full aperture had had more detail visible in the
> viewfinder than he got in the final photos -- the answer was that the
> lens was sharper 'stopped down' by the viewing system than it was at
> the full aperture that formed the actual on-film image.
From Rangefinder mailing list:
Date: Wed, 23 Oct 2002
From: Jeffery Smith jsmith45@bellsouth.net
Subject: RE: Age: RF vs SLR
The muscles are fine, but the lens itself loses its elasticity. Since it
is, by default, at the flattened condition (ligaments pulling it flat
from the edges), the lens remains flat instead of rounding up when you
try to focus up close.
I'm so near-sighted, my eyes focus normally at about 5 inches. Take off
my glasses and try to read a billboard...no go!
Jeffery
drayton cooper wrote:
> Bill has touched on the real answer to the original question of why we
> find focusing more difficult as we age. There is one over-riding reason
> which affects us all, sooner or later, and a second, complicating factor
>
> which affects many of us.
>
> The universal factor is called "presbyopia", "old eyes". It is a
> condition that causes the muscles of the eye to lose their elasticity,
> effectively limiting the range of focus on near objects. It's the reason
>
> bi-focals were invented.
>
> The other reason is the development of cataracts on our eyes, another
> by-product of aging (and other factors) for some of us. Cataracts are
> caused by a thickening of the eye's lens and serve as nature's own
> neutral density filter, limiting the amount of light that gets through
> the iris.
>
> These two reasons account for the growing popularity of Leicas, Bessas
> and Contax G's among us older geezers. And you thought it was all about
> status!
>
> DC
>
> Bill Salati wrote:
> > Another factor is the eye's difficulty in focusing on closer objects as our
> > age progresses. With a rangefinder you are viewing an aerial image. In an
> > SLR your viewing the image on a focusing screen. The screen's apparent
> > distance from the eye varies with different finder types and manufacturers.
> > In some SLRs the apparent image is nearer and more difficult for the aging
> > eye to focus on.
> > At age forty eight, I still see well without glasses but I am favoring my RF
> > over my SLRs for focusing wide angle lenses.
> >
> > Bill
From rangefinder mailing list:
Date: Thu, 24 Oct 2002
From: Dante Stella dante@umich.edu
Subject: Re: [RF List] Can a Lens be brighter than no Lens at all
Greg, I think you're right - it's projection, not sensitivity.
The figure that f/2 is equivalent to the human eye *lens'* light
gathering ability appeared in my Autoreflex T manual from 1967. I
assume that the sensitivity is for an equivalent time slice - like 1/125
of a second and onto film, not a finder. That is totally believable.
Sure, you can let your eyes adjust to light, but you totally lose color
vision, depth of vision, and any sense of detail, just like when you
severly underexpose a frame. Looking at something for 30 seconds in the
dark, you might see something. But it will be completely lacking in
detail. That's just like opening an f/2 lens for 30 seconds.
I think a lot of SLRs suffer because they lose light at several stages:
Lens - A good lens made after 1967 will lose up to 5% of the light to
reflections. The better lenses have 1% or less on-axis flare, meaning
they are transmitting 99%.
Mirror - I have read that an SLR mirror normally reflects about 90% of
the light. AF mirrors do a lot less - like 66%.
Screen - if the plastic focusing screen has yellowed, you lose a little
bit there. You lose a little by virtue of the ground surface as well.
Prism - again, in a coated glass prism, a couple of points. A mirror
box prism, more.
I think that in a finder, a 1.4 is breaking even, and on film, twice as
good. I think that once you're in the f/1.2 to f/1.0 class, the SLR
has it - because the finder gets brighter and compositional focus can
easily be done. For teles, I think that they bring in light from
further, but the constraint is still the aperture.
By the way, in a highly unscientific test, I took my Zone VI spotmeter
and pointed it through the center of my M3 finder (one of the cleanest I
have ever seen) and directly at the subject. Difference: 3 stops. Did
the same through my Nikon FA with K2 screen and 105/1.8. Also 3 stops
difference.
Dante
Gregory Levonian wrote:
> Hi,
>
> I don't have any special knowledge on this issue except what I read in your
> email, but I think you pretty much completely are misunderstanding
> things.
>
> It's not a question of how sensitive the eye is at detecting light, but
> rather how much light is being projected into the eye. If the lens has a
> field of vision less than (or equal to) the angle of view of an eye, than
> clearly it can't manufacture extra light - the lens is just going to (among
> other things) filter some light out. If however it is wider than what the
> eye sees it will still filter out some of the light, but it will also
> "gathers" the light and project it to the retina. If the amount it gathers
> is greater than the amount it filters it does have the possibility of being
> brighter than an unaided eye.
>
> The sensitivity of the eye has nothing to do with this, just as the film
> speed does not affect the speed of the lens.
>
> I hope this helps.
...
From: Don Stauffer stauffer@usfamily.net
Newsgroups: rec.photo.film+labs,rec.photo.equipment.35mm
Subject: Re: Film still doesn't match human eye sensitivity in low light
Date: Wed, 25 Dec 2002
Tests show human eye can perceive a flash of 3 to 5 photons. Best
electronic equipment can perceive flash with about 2 photons, so eye is
very close to photon-limited.
Of course, it has other failings. As someone else points out, it cannot
accumulate much exposure. It CAN integrate SOME, I think for up to a
period of about 100 milliseconds, but electronic equipment can integrate
for far longer.
AC/DCdude17 wrote:
> Our scotopic vision(the mode our eyes are in at very low light
> level) is an amazing thing. After you lay in your bed for good half an
> hour or so, the light shining through the blind from street light or
> whatever is often enough to let us see monochrome image of your
> furnitures and if you move your head around, you can see the next
> furniture instantly. Close your eyes. Open them. You can see the
> image almost instantly and if we were to convert that into ISO
> equivalent, I think it will come out VERY high.
>
> I did an experiment with a film and I can tell you that even so
> called fast film doesn't perform anywhere near as well as our eyes.
>
> Lens: Pentax 50mm F2.0
> Aperture: F2.0
> Film: Fuji Superia X-TRA ISO 800
>
> Exposure durations and result:
>
> 2s nothing, 4s nothing, 8s nothing, 15sec nothing, 30 sec nothing, 1min
> very slightly exposed, resolution is still much poorer than what I can
> see.
>
> All the light I had was a faint glow of green LEDs from an alarm clock
> at the other end of room and a bit of high pressure sodium light peeking
> through the blind.
>
> Even 800 speed film at F2.0 required a good minute to get any image, so
> even with 3200spd film and F1.4 lens, it will theoretically take good
> 20seconds to get same density.
>
> Is it possible to capture what we see in the dark on film within the
> timeframe required to let our eyes see it strictly in available light
> mode?(no more than a sec I'd say)
>
--
Don Stauffer in Minnesota
From: "Tony Spadaro" tspadaro@ncmaps.rr.com
Newsgroups: rec.photo.film+labs,rec.photo.equipment.35mm
Subject: Re: Film still doesn't match human eye sensitivity in low light
Date: Wed, 25 Dec 200
Except that the eye cannot retain light they've gathered. I walk around at
night at lot, and I photograph at night. I've done 4.5 hour exposures on
moonless nights in areas illuminated only by light bounced off the bottoms
of clouds. The scenes are in colour although they have a strange quality to
them.
As far as trying to capture low light faster, you can re-rate P3200 as
high as 12500 - another two stops beyond the nominal EI of 3200, but I know
of no film that can be rated higher than that and still capture light
without being overcome by fog in the developing stage.
--
http://chapelhillnoir.com
and partial home of
The Camera-ist's Manifesto
The Links are at
http://home.nc.rr.com/tspadaro/links.html
From: "Michael A. Covington" look@www.covingtoninnovations.com
Newsgroups: rec.photo.film+labs,rec.photo.equipment.35mm
Subject: Re: Film still doesn't match human eye sensitivity in low light
Date: Wed, 25 Dec 2002
...
> Is it possible to capture what we see in the dark on film within the
> timeframe required to let our eyes see it strictly in available light
> mode?(no more than a sec I'd say)
>
Well... The brightness range of the human eye is more than a million to one.
Full sunlight is a million times brighter than full moonlight, and we can
see things under considerably less illumination than full moonlight. The
actual usable range is probably more like 100 million to one.
On 800 speed film, you can photograph a brightly sunlit scene in 1/1000
second at f/16. The maximum exposure you have in mind is probably 1 second
at f/1.8. That's 300,000 times more exposure.
Somewhere we need to find another factor of 300, very roughly. So... No,
we're not there yet. If you had 32,000 speed film, and a 5-second exposure,
and an f/1 lens (which Canon makes, though it's not too sharp), you'd be
there.
Pushing film to EI 32,000 *may* be possible if you use *all* the tricks:
Black-and-white film with a wide spectrum range (such as the
now-discontinued Kodak 2475 Recording Film); extreme development; and some
preflashing or chemical hypersensitization before the exposure. However,
with film of this type, reciprocity failure would cost you quite a bit of
speed in 1-second or longer exposures. T-Max P3200 might be a better film
to start with.
(Don't expect color. Each layer of color film responds to less than 1/3 of
the spectrum. You need the whole spectrum in one image.)
There are also CCDs like the ones used in astronomy. Their sensitivity is
about the same as film (400 speed) but they are very linear (which means you
can "push" an underexposed image by amplifying it) and they have no
reciprocity failure.
An experienced astronomer can take "exposures" of up to 10 seconds with the
human eye, during which things fluctuate into and out of visibility.
At that point you are detecting nearly every photon, and further improvement
would be possible only by taking longer exposures and/or covering more than
just the visible spectrum.
--
Clear skies,
Michael Covington -- www.covingtoninnovations.com
Author, Astrophotography for the Amateur
and (new) How to Use a Computerized Telescope
Date: Mon, 3 Feb 2003
From: DaveHodge@aol.com
To: hasselblad@kelvin.net
Subject: [HUG] Re: hasselblad V1 #1845
hasselblad@kelvin.net writes:
Try staring at a stationary LED in a totally dark room, and you would
swear it is dancing around after a while.
It is. Involuntary eye movements are needed to keep the visual receptors
from saturating. If you deliberately stare at something for a few seconds it
will disappear because the retinal sensors get saturated and stop sending
signals to the brain. In a dark room the involuntary eye movements make the
LED look like it is dancing. If it did not dance, it would disappear!
From rangefinder mailing list:
Date: Wed, 23 Oct 2002
From: Dante Stella dante@umich.edu
Subject: RE: [RF List] Age: RF vs SLR
Nick:
The interesting thing is that SLR finders, especially the pre-AF ones, can
be brighter than life once the lens hits f/1.4 or faster. F/2 is
equivalent to the light the human eye sees. Assuming that there is a
1-stop loss in the finder system (that would actually be huge), it should
be easier to focus SLRs in low light with f/1.4 lenses and faster. I just
bought a Nikon FA and was blown away by how bright the finder was against
an autofocus SLR finder.
Dante
...
From rangefinder mailing list:
Date: Wed, 23 Oct 2002 17:10:51 +0000
From: drayton cooper
Subject: RE: Age: RF vs SLR
Bill has touched on the real answer to the original question of why we
find focusing more difficult as we age. There is one over-riding reason
which affects us all, sooner or later, and a second, complicating factor
which affects many of us.
The universal factor is called "presbyopia", "old eyes". It is a
condition that causes the muscles of the eye to lose their elasticity,
effectively limiting the range of focus on near objects. It's the reason
bi-focals were invented.
The other reason is the development of cataracts on our eyes, another
by-product of aging (and other factors) for some of us. Cataracts are
caused by a thickening of the eye's lens and serve as nature's own
neutral density filter, limiting the amount of light that gets through
the iris.
These two reasons account for the growing popularity of Leicas, Bessas
and Contax G's among us older geezers. And you thought it was all about
status!
DC
Bill Salati wrote:
> Another factor is the eye's difficulty in focusing on closer objects as our
> age progresses. With a rangefinder you are viewing an aerial image. In an
> SLR your viewing the image on a focusing screen. The screen's apparent
> distance from the eye varies with different finder types and manufacturers.
> In some SLRs the apparent image is nearer and more difficult for the aging
> eye to focus on.
> At age forty eight, I still see well without glasses but I am favoring my RF
> over my SLRs for focusing wide angle lenses.
>
> Bill
From rangefinder mailing list:
Date: Wed, 23 Oct 2002
From: "charlie" charlie@highhill.com
Subject: Re: [RF List] Age: RF vs SLR
And as someone who has had cataract surgery, first in one eye and then in
the other 5 years later, there is another by product of age that might be of
interest - that is that the lens of the eye begins to yellow as you get
older. Of course you can't really notice this unless you have your lens
removed, but before my second operation, I noticed a fairly striking
difference between my real and my "plastic" lens - almost like holding a
light yellow filter up in front one eye. It's a good thing I'm a B&W; guy or
balancing colors would have been quite tricky!!!
And of course post operation, I have picked up maybe a stop of brighness,
which making focusing easier - as long as objects aren't too close.
charlie
...
From rangefinder mailing list:
Date: Wed, 23 Oct 2002
From: Jim Williams jimwilliams1@cox.net
Subject: Re: [RF List] Age: RF vs SLR
Dante Stella wrote:
> The interesting thing is that SLR finders, especially the pre-AF ones, can
> be brighter than life once the lens hits f/1.4 or faster. F/2 is
> equivalent to the light the human eye sees.
Just out of curiosity, what's the basis for this assertion? I realize
that the lens in the eye has a (variable) focal length and a maximum
aperture (which probably varies in size from person to person, although
possibly not all that much) but the process of 'seeing' is considerably
different between the eye and a piece of film. I recall reading (I
believe in 'Q.E.D.', by Richard Feynman) that if you're young, healthy,
and give your eyes plenty of time to adapt to darkness, they can detect
bursts of light amounting to as little as eight individual photons. I
don't know how one would go about relating that figure to the amount of
light a lens 'sees', but I would guess that a piece of film would have
to accumulate light over an exposure of several seconds to register
that amount of illumination.
What that translates into is that I don't think a lens with a larger
numerical aperture would act as a 'funnel' to make the scene appear
brighter than you'd see it with your bare eyeball. If it would, the
Army could save all that money it spends on those electronic
night-vision systems and just fit the soldiers with great big
eyeglasses, right?
> Assuming that there is a
> 1-stop loss in the finder system (that would actually be huge), it
> should
> be easier to focus SLRs in low light with f/1.4 lenses and faster.
Another factoid dredged out of my sometimes dubious memory: seems as if
I recall (in one of Norman Goldberg's technical articles in the old,
more-technical 'Pop Photo') that because the condenser in an SLR
viewing system limits the illumination angle on the focusing screen to
the central portion of the lens' exit pupil, you're always focusing
through an effective aperture no greater than about f/2.8, no matter
how fast the lens you mount on the camera. This was noted in answering
a reader's question about why some pictures he had taken with a long,
fast tele lens at full aperture had had more detail visible in the
viewfinder than he got in the final photos -- the answer was that the
lens was sharper 'stopped down' by the viewing system than it was at
the full aperture that formed the actual on-film image.
From: "Ron Andrews" randrew1@rochester.rr.com
Newsgroups: rec.photo.film+labs,rec.photo.equipment.35mm
Subject: Re: Film still doesn't match human eye sensitivity in low light
Date: Thu, 26 Dec 2002
A few weeks ago, there was a thread on rec.photo.digital discussing the
"specs" of the human visual system as if it were a camera. My conclusion was
that the equivalent ISO speed of the eye ranges from 10 to 1600 for photopic
(color) vision. I guessed at an equivalent speed of somewhere between 10000
and 50000 for scotopic vision. The experiment of AC/DCdude17 would put this
at the higher end of that range.
FWIW, here is a copy of my prior post:
Humans have binocular vision, so we should compare to a stereo camera.
The focal lengths are about 25mm.
The apertures go from about f/3 to f/10.
The human visual system doesn't take snapshots. It is more like a video
system with a continuous response. Thomas Edison and others established the
flicker fusion frequency of the human visual system at about 40 to 50 cycles
per second. This gives us an estimate of the shutter speed.
We have normal color vision down to around 7 foot candles. If we assume
an f/3 aperture and 1/50th second shutter speed, the equivalent ISO speed is
about 1600. Of course we also have normal color vision in bright sun (8000
fc). At f/10, this is equivalent to about ISO 10. The latitude for normal
color vision is over 8 stops.
The rods in the retinas are sensitive to much lower light levels. I'm
not sure if the flicker fusion frequency is the same, but I'll guess that
the equivalent ISO is somewhere between 10000 and 50000.
So how many pixels are in the retina? The analogy breaks down here
because the eye packs a lot of rods and cones into the fovea, the small
central area of the retina. The rest of the retina has fewer receptors. We
"see" an entire seen at high resolution because our eyes scan across it. We
really only see the center part of a scene at high resolution. In any event
we can attempt to compare resolutions in terms of cycles per degree. The MTF
curve of the eye has some response out to about 50 cycles per
degree depending on the aperture. If a digital camera has a 45 degree angle
of view, it would require 4500 pixels across the width (2 pixels to record
one cycle) and about 3000 on the vertical axis for about 13.5 Megapixels to
perfectly reproduce what the eye sees. Of course the response at 50 cycles per
degree is rather low so a camera with resolution half as good (say 6 MP) would
reproduce most of what the eye sees.
The spectral sensitivities of the three different types of cones peak
at 450, 550, and 590 nm. with broad areas of overlap. The retina and the
brain do a great job of matrixing these signals into our color response.
Here is a useful article that covers come of these issues:
http://www.stanford.edu/class/ee368b/Handouts/09-HumanPerception.pdf
"AC/DCdude17" JerC@prontoREMOVETHISmail.com wrote
> Our scotopic vision(the mode our eyes are in at very low light
> level) is an amazing thing. After you lay in your bed for good half an
> hour or so, the light shining through the blind from street light or
> whatever is often enough to let us see monochrome image of your
> furnitures and if you move your head around, you can see the next
> furniture instantly. Close your eyes. Open them. You can see the
> image almost instantly and if we were to convert that into ISO
> equivalent, I think it will come out VERY high.
>
> I did an experiment with a film and I can tell you that even so
> called fast film doesn't perform anywhere near as well as our eyes.
>
> Lens: Pentax 50mm F2.0
> Aperture: F2.0
> Film: Fuji Superia X-TRA ISO 800
>
> Exposure durations and result:
>
> 2s nothing, 4s nothing, 8s nothing, 15sec nothing, 30 sec nothing, 1min
> very slightly exposed, resolution is still much poorer than what I can
> see.
>
> All the light I had was a faint glow of green LEDs from an alarm clock
> at the other end of room and a bit of high pressure sodium light peeking
> through the blind.
>
> Even 800 speed film at F2.0 required a good minute to get any image, so
> even with 3200spd film and F1.4 lens, it will theoretically take good
> 20seconds to get same density.
>
> Is it possible to capture what we see in the dark on film within the
> timeframe required to let our eyes see it strictly in available light
> mode?(no more than a sec I'd say)
From: John@Stafford.net (John Stafford)
Newsgroups: rec.photo.film+labs,rec.photo.equipment.35mm
Subject: Re: Film still doesn't match human eye sensitivity in low light
Date: 27 Dec 2002
To add to Ron Andrews' good information, the human eye does not see
all the colors in the narrow spectrum called 'visible light'. There
are flaws in the analog firmware of the retina that make it
exceedingly difficult (if not impossible) to differentiate certain
colors when they are placed on or near another color (specific
examples are available.) Further, there are some colors that can be
created (mixed - additive or subtractive) using different combinations
of other colors. If our eyes did accurately sense all colors in the
visible range, that would be impossible.
--
jjs - Black and White Photography _is_ Color Photography
From: "Eugene A. Pallat" eapallat@apk.net
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Calling Hemi's Bluff (Viewing Distance)
Date: Tue, 04 Mar 2003
Let's get rid of the hype and get down to reality.
The American Opthalmic (sp) Society states that the average vieing
distance is 15 inches. That's how far away the average person holds any
hand held printed meterial to read, or a photograph to view.
15 inches is 381 mm. In order to determine the degree of enlargement of
a negative to give propper viewing perspective, use yhe following formula.
Divide the viewing distance by the focal length of the lens.
This gives the degree of enlargement required for the negative.
Multiply the enlargement factor by the dimensions of the negative.
For example, consider a 3 inch (75mm) lense on a 4x5 view camera.
15/3 = 5 times enlargement.
That means a 20 x 25 inch print is required. You can also charge more
for your work! ;-)
When you look at that print at 15 inches and then the actual scene
photographed, everything will be in the propper proportion and perspective.
This is the standard method used in forensic photography. Anything else
will give a distorted view and photographers have even been impeached by
the courts for falsifying evidence done otherwise.
Naturally, macro work is in a different catagory.
Gene Pallat
Orion Forensics
From: "Eugene A. Pallat" eapallat@apk.net
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Calling Hemi's Bluff (Viewing Distance)
Date: Wed, 05 Mar 2003
J Stafford wrote:
> Where did the 15 come from?
Opthamologists noted that the average person holds printed matter and
photographs 15 inches from the eye.
Unless you're so far sighted you hold it at arms length. ;-)
Gene Pallat
Orion Forensics
From: nulldev00@aol.com (Edward Green)
Newsgroups: sci.optics,sci.optics.fiber,sci.physics
Subject: Re: Eye Nonlinear Response
Date: 14 May 2003
youzpalang@netscape.net (Djamshid - Navabi) wrote
> Hi:
>
> I was standing about 10 meters from a window at the end of a hall of
> about 3 meters wide looking at a hill some distance away(sunny clear
> sky). It seemed that objects (like trees and houses)on the hill were
> more resolved and clear than when I was right at the window looking at
> the whole (eyes' field of view) scene. The hall had bright
> fluorescent lights (no more eye pupil dilution than when standing by
> the window). Is this due to some kind of nonlinear response of the
> eye under the above condition, or are my eyes screwed up?
I don't know ... there are a string of variables. There is a dense
spot of receptors on the retina ... when you look at the scene from
down the hall, it may have just spanned this dense spot and really
have been sharper ... on average ... than when it filled your whole
retina. Of course if you focussed your attention on a small part of
the scene when it filled your field of vision, actual angular
resolution would have been just the same.
A related question ... the picture on small screen TV's often seems
much sharper and more intense than on large screens. In many cases it
actually is, since the same number of pixels are simply spread over a
larger area -- though high definition TV's are changing this. But in
general this shows how stupid and exhibitionist the large screen TV
is. The only reason to inflate a given picture resolution is to get
farther back from it and have it fill the same space on your retina
... and like your outside picture which looked sharper framed by the
window, the experience is probably best when the screen does not fill
your entire visual field.
So the only damn practical reason to have a screen larger than one
which can be comfortably watched by a few people at a few feet is if
you actually plan to have 30 people watching! For individual viewing,
I find a compact set at a distance of a few feet better. Of course a
huge screen TV shows you are powerful and have a large ph*llus, which
I suppose contributes some economic value.
From: "Danny Rich" DannyRich@softhome.net
Newsgroups: sci.optics
Subject: Re: Eye sensitivity
Date: Tue, 10 Jun 2003
Check out the following web page:
From the Color Vision Research lab. It will have tables of V-lambda at fine
intervals versus both wavelength and frequency, both linear and logarithmic.
By the way - one poster mentioned that this curve is the sum of three
curves. Those component curves are also given. All of these curve
interpolate or model better as log functions since they are related to
absorption bands and have an exponential nature. Modeling exponential
functions with polynomials is usually not very fruitful. Modelling
log(exponential functions) with polynomials is much better.
Danny
"Richard F.L.R. Snashall" rflrs@notrcn.com wrote
> The curve of eye sensitivity given in Born & Wolf looks (to me)
> quite a like a "bell" curve, but it is somewhat skewed. The
> peak (0.555 microns), however, would be nearer the center if
> it were plotted against frequency instead. Assuming that it
> would look more like that bell curve if so plotted, I did a
> quick calculation and came up with a mean of about 0.54 and a
> standard deviation of about 0.041 for light measured in
> 1E15 hz.
>
> Is there an traditional estimator for this curve that is used?
>
> Rick S.
From: "James R \(Jim\) Lynch III" jrlynchiii@attbi.com
Newsgroups: sci.optics
Subject: Re: Eye sensitivity
Date: Mon, 09 Jun 2003
If you're doing lens design for a visual system and need spectral weightings
for the photopic or scotopic eye, you can't beat CodeV's SPEctral option. It
will convolve the source with the eye to give spectral weightings for any
number of wavelengths up to 21. SYNOPSYS also has a nice feature similar
CodeV for calculating these weights.
I've been using the spectral weights and wavelengths given in Table 4.1b
"Color Sensitivity" in "Telescope Optics" by Rutten & van Venrooij:
TABLE 4.lb, Color Sensitivity
Wavelength Relative Response
Photopic(*2) Scotopic(*3)
436 nm <.02 .28
486 nm .20 .86
513 nm .60 1.00
555 nm 1.00 .40
587 nm .80 .06
656 nm .08 <.01
(*2) Photopic: bright enough to see color
(*3) Scotopic: too dim for color
James R. Lynch III
...
From: "Harvey" xh.ruttx@ecs.soton.ac.uk
Newsgroups: sci.optics
Subject: Re: DOF and human eye question
Date: Tue, 15 Jul 2003
"Acme Optics" acmeoptics@earthlink.net wrote
> Jim Hahn james.hahn@comcast.net wrote:
> Yes. Think about it this way. As the aperture gets smaller, 2.44
> lambda/aperture diameter gets bigger in object space and so 2.44 x
> lamda x f# gets bigger at the focal plane. Given fixed size
> deterctors, pretty soon the diffraction blur dominates over
> geometrical focus blur. I'd look at the equations in Optical
> Engineering by Warren Smith.
The eye is not diffraction limited by a *good* factor.
If I recall correctly the resolution is usually quoted as about one arc
minute, but Im not sure if that is wide open or stopped down.
Typically I can see far more detail in *bright* light - eye stopped down -
than in dim - eye wide open - which suggests abns etc dominate, not
diffraction, because its in focus all the time, bright or dim.
*Depth* of focus of course increases as you stop down; it ought to be easier
to see the rifle front sight & target in focus in bright light.
Not really suprising that a blob of soggy liquid & jelly of dubious shape &
refractive index uniformity doesnt quite get to >Part two: My eyes are 56 years old. So I find that having a prescription
> >lens helps too. I can add any lens to the system. I am guessing that
> >this lens is essentially setting the "exact focus" distance of the
> >optical system. Does that play into any formula? I have seen some
> >formulas into which one plugs the near, far, and exact focus distances.
>
> Your lenses are less flexible and so your muscles can change focal
> length less than they could when younger, so we compensate with bi or
> tri-flocals. It sucks but since it is not life threatening, the
> solution takes a back seat to the really nasty little things that can
> go wrong.
My optician reckons that by 56 many people can hardly accomodate at all.
And notes that one good point about eventually getting cataracts is that
after the operation whilst you cant accomodate at all they can correct out
the basic (for me) -6D error & I wiont be short sighted any
more................
Get a focussable telescopic sight & the cross wires & target can both be
nicely in focus; as the grey sqiurrels & wood pidgeons in my garden know to
their cost.................
Harvey
From: Louis Boyd boyd@apt0.sao.arizona.edu
Newsgroups: sci.optics
Subject: Re: Exit pupils, light gathering & the eye
Date: Thu, 18 Sep 2003
Rico Tudor wrote:
> Given a 7mm entrance pupil for the human eye, light-gathering by ordinary
> 8x binoculars hits a limit at 8x56. Is this an optical inevitability, or
> can a direct-view 8x200 be designed such that all light reaches the retina?
>
Yes, an optical inevitability. Conceivably some eye surgeon could come
up with a replacement eye lens that would replace your approximately F/3
eye lens for an F/1 unit which would give about a factor of 10 light
boost but it would make you look a bit odd. A side effect would be
that you'd have horrible depth of field. Until then your choice is to
use an image intensifier or some other form of imaging device.
Using that 200mm objective you can boost the magnification to about
200/7 or about 28 power and actually use the light that big lens
collects. That does work fairly well in low light because it partially
makes up for the low resolution of the human eye caused by the low
density of of the high sensitivity rods in the eye. You see this used
to good effect in the huge Russian "border guard" binoculars that are
kicking around the surplus market. No, they're still not as sensitive
as intensifiers and they cost more.
Contrary to popular opinion the advanatage of image intensifiers isn't
because because their photcathodes are so much more sensitive than the
human eye.
1. Their gain keep the brighness high enough that the high resolution
cones in the fovea are usable. This alone yields about a 10x
improvement in resolution over the dark adapted eye.
2. They take in a wider portion of the spectrum, particularly Gen III
tubes which have good sensitivity in the 700-900 nm range where sky
glow is much brighter than in the visible. Using the whole spectrum
from 300 to 950 nm (with the skyglow) gives about a 10x improvement over
just using the less than 400-600 nm range of the dark adapted eye.
3. Their flat photocathode doesn't limit the acceptance angle so fast
lenses are usable. An F/0.5 optical system (Viet nam era TVS-2 and TVS-4
for example) offers about 36x improvemnt over the eye's F/3 lens. Most
modern NV goggles use about an F/1 lens which still gives a 9x improvement.
4. They do provide some quantum efficiency improvement over the human
eye giving about a 4x improvement.
Actually one of best and cheapest night vision devices, and the only
common one which retains high resolution color vision, is a flashlight.
--
Lou Boyd
From Leica Mailing List:
Date: Tue, 3 Feb 2004
From: LRZeitlin@aol.com
Subject: [Leica] Human color vision and the cone photoreceptors.
To continue to beat a horse of a different color, this is a long post,
extracted from current research literature, explaining the assertion that there are
more than three types of color receptors in the human eye. The trichromatic
theory of color vision is not invalidated, as such, but it has been
significantly modified. It helps explain why we can see colors that we cannot normally
photograph and why people disagree on the exact color match of pieces of fabric.
(This is my problem when my wife takes me shopping with her.)
A long accepted fundamental property of human vision is trichromacy. The
trichromatic theory helps to explain our color perceptions and color
discriminations. The anatomical basis of trichromacy begins with the complement of cone
photoreceptors in the retina. For over one hundred years researchers thought that
the color-normal eye contained three cone types, designated as S, M, and L,
whose photopigments were later psychophysically estimated to have peak spectral
sensitivities near 440, 540, and 560 nanometers. There is considerable
overlap in sensitivity of the middle wavelength sensitive and long wavelength
sensitive cone types.
Over the years, however, psychologists questioned whether subtle variations
may exist in normal color vision based on small individual differences in the
spectral sensitivities of the photopigments (Alpern & Wake, 1977; Neitz &
Jacobs, 1986). The findings of the early studies were viewed with some skepticism,
however, because of the difficulty in ruling out measurement error and
confounding factors. As the psychophysical evidence grew, researchers began to
investigate this possibility from many angles.
Today, psychophysical (Neitz & Jacobs, 1990; Mollon, 1992),
microspectrophotometric (Dartnall, Bowmaker, & Mollon, 1983), and molecular genetic studies
(Nathans, Piantanida, Eddy, Shows, & Hogness, 1986; Winderickx et al., 1992)
provide evidence of substantial variation in the number and spectral sensitivity
of the cone types in the color-normal eye (also see Mollon, Cavonius, and
Zrenner, 1998). The evidence now suggests the presence of three broad families of
normally occurring cone photopigments. There is thought to be only one
photopigment with a peak spectral sensitivity in the short wavelengths (blue), but
there is now evidence that there are multiple middle wavelength (green)
photopigments and multiple long wavelength (red) photopigments. The difference in
spectral sensitivity among the middle wavelength pigments or among the long
wavelength pigments has been estimated to be approximately 5-7nm(Neitz, Neitz, &
Jacobs, 1995). In fact there may be as many as 9 different cone types with various
peaks in photosensitivity among the middle and long wavelength families.
Molecular genetic analyses show that individuals may inherit a surprisingly
large number of different X-linked, recessive genes that encode the production
of these photopigments (Neitz, Neitz, & Grishok, 1995). An obvious question is
why do we have so many color vision genes? The genes that encode the middle
and long wavelength sensitive pigments reside near the end of one of the arms
of the X chromosome and they have very similar DNA sequences. In fact, the
substitution of one amino acid in the DNA of a photopigment gene is sufficient to
cause a change in the spectral sensitivity of that photopigment and in our
color perceptions. The location and similarity of these genes makes them
susceptible to the kinds of genetic errors that produce multiple gene copies, as well
as hybrid genes that are genetic composites of the original ones (Nathans, et
al., 1986).
At present, it appears that normal color vision results from inheriting at
least one cone type from each cone class (short, middle, and long). It is
unclear, however, which complement of genes and cone types result in specific types
of color vision deficiency. There is a great deal of genetic variation among
individuals with the same type of color defect, making this work difficult.
However, it appears that both the type and severity of a color vision defect can
be linked to the complement of different cone types in the retina. Hybrid
genes, which have been associated with small differences in the spectral
sensitivity of the photopigments, are thought to be involved.
These findings lead to an interesting question: if humans possess more than
three cone types in their retina, do they still have trichromatic vision? The
answer appears to be yes, presumably because the outputs of the different
middle or longwavelength cone photoreceptors are summed together before leaving the
retina. The resulting signals differ to a small but significant degree across
individuals, though, because they affect color perception in some situations.
Individuals with different complements of cone pigments will not accept each
other's color matches in the long wavelength end of the spectrum and they will
disagree on color names for certain wavelengths of light (Neitz, Neitz, &
Jacobs, 1993). For example, a particular mixture of red and green light might
appear a perfect yellow to your eye, but appear a greenish-yellow or slightly
orange to someone else. This type of color vision assessment, called the Rayleigh
Match, is the most accurate method for measuring color discrimination and
diagnosing the congenital color vision defects.
The distribution of photoreceptors in the retina appears to be nearly random.
The ratio of R / G / B cone types varies, but the long wavelength cones are
the most prevalent; short wavelength cones the least prevalent in the retina.
Women who are heterozygous for the normal complement of color vision genes, th
erefore, may have a mosaic retina: a patchwork of color-normal and
color-deficient regions (Cohn, Emmerich, & Carlson, 1989). The nature of this mosaic
depends on the inherited complement of color vision genes and on the point in
development that X-chromosome inactivation occurred. That is, some women
heterozygous for these genes may develop a color vision deficiency while others may
develop normal color vision (Miyahara, Pokorny, Smith, Baron, & Baron, 1998).
And, in fact, there are reports in the literature of identical (monozygotic)
twins where one twin has normal color vision and the second is color-deficient
(Jorgenson, et al., 1992).
In light of these current findings, sensory psychologists and other
perception researchers are designing psychophysical tasks to try to tease apart the
nature of color processing in the eyes of individuals with different complements
of cone photoreceptors. The challenge will then fall to neuroscientists,
molecular biologists, and others to support or refute these findings at the
cellular level.
Future work for sensory psychologists will also involve investigating the
extent to which these individual differences in color vision affect interactions
with the world. Society uses color to code information in a variety of
settings, including art. photography, education and transportation. In many
occupations color discrimination is critical, for example, in discriminating electrical
wiring and colored signal lights or in medical research. While these
individual differences are small, they may prove to be problematic in some settings.
In contrast to the research directed at the earliest stages of sensory
processing, today there is also substantial exciting research interest at the other
end of the S&P; continuum: This research is directed at higher level perceptual
processes and phenomena in the gray area where perception and cognition meld.
Culture, desire, expectation, and learning are as important in determining
what we see as the sensation itself.
Larry Z
From: john@xyzzy.stafford.net (jjs)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Resolution -- 8x10" Prints
Date: Sat, 21 Feb 2004
KBob KBob@nowhere.net wrote:
> Raphael Bustin rafe.bustin@verizon.net wrote
> [...]
> Yes, of course you're right - what the hell was I thinking of?? The
> human eye, under optimal viewing conditions can resolve up to 30 lp/mm
Let us get realistic here. You are unlikely to discern 30 lp/mm except
perhaps under abstract and unrealistic conditions while viewing a very
uninteresting subject. The subject at hand is photographic prints and not
viewing line pairs in a lab under ideal conditions.
First, the eye resolves best at ten inches. Second, it discerns line-pairs
best if the are, in fact, like line pair (for example, three parallel
human hairs, at least three pixels) and of high contrast. Another big
issue is that the eye must have enough light to close the iris to about
2.5mm in diameter (a bit larger axial). That is not average or even an
ideal gallery condition.
So, unless you view prints in an exceedingly uncomfortable and abstract
circumstance, your "30 lp/mm" is meaningless.
6 to 12 is more realistic, FAPP.
From: KBob KBob@nowhere.net
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Resolution -- 8x10" Prints
Date: Sun, 22 Feb 2004
Raphael Bustin rafe.bustin@verizon.net wrote:
>KBob@nowhere.net wrote:
>>A 14 MP image from a 14n (full frame 35mm CCD) demonstrates that
>>digital images of up to about 12X18 rival those of film. That may
>>also apply to the Canon EOS 1Ds. These cameras are intended to rival
>>medium format film types, and they appear to succeed--and it's not
>>only the original image resolution that is the issue here.
>>
>>With film you also have other gremlins at work to degrade the image,
>>most notably in the enlarging process where various scattering effects
>>and further degradation from the enlarging lens and illumination
>>system must be considered. The exquisite detail and gradation present
>>for large-format contact prints can be achieved with digital, since
>>you have far superior control over tonality, setting of white & black
>>points and gradation--and no gremlins or grain.
>>
>>Under normal illumination the human eye can resolve about 230-300
>>lp/mm on a print, and that's just about what an inkjet print is
>>capable of. Image resolution beyond this has rapidly diminishing
>>returns. Print resolution and CCD megapixels cannot be directly
>>compared, but as a general rule of thumb a visually optimal 8X10 can
>>be produced by a 5 MP image. You can extrapolate from this to show
>>that a 12X18 requires about 14 MP.
>
>
>I think your numers are off in that last paragraph.
>
>I've heard Bob M quote figures of 10 lp/mm for
>prints, which is in the same ball park as typical
>inkjet "resolutions" in the 250-350 lpi range.
>
>FWIW, Lightjet's native (contone) resolution is
>305 lpi, Durst Epsilon is 254.
>
>rafe b.
>http://www.terr
Yes, of course you're right - what the hell was I thinking of?? The
human eye, under optimal viewing conditions can resolve up to 30 lp/mm
I understand, but under more normal conditions this drops to more like
10-15 lp/mm (as you noted). What I meant to say was that a printer
having 230-300 DPI (not lp/mm) provides an image that generally
corresponds with what the human eye can resolve under normal viewing
conditions.
From camera makers mailing list:
Date: Wed, 25 Feb 2004
To: cameramakers@rosebud.opusis.com
From: "R. Mueller" r.mueller@fz-juelich.de
Subject: [Cameramakers] Silicon Sensor with filter to approximate human eye response
This morning I discovered a reference to a sensor which might satisfy the
needs of some of you who want to build a photometer offering a spectral
response near that of the human eye. You will find a data sheet at
http://www.osram.convergy.de/upload/documents/2003/12/12/16/01/sfh2430_2003-09-25.pdf
I should offer some cautionary notes;
1) The manufacturer claims the sensitivity is close to that of the eye; I
have not compared the given curve to the response of a standard eye.
2) I am not sure you want match anyway! You would want a response
resembling that of a film, I would expect. But different films have
different spectral characteristics.
3) The spectral response of the eye varies with light level at the lower
levels (becoming monochromatic at quite low levels.) The response of most
sensors is pretty much level independent.
4) I believe I once saw a recommended response for light meters; I think
it was reproduced in a photographic encyclopedia, but which I am not
sure. Maybe somebody can shed some light on this.
5) I have no idea where you can buy these, though if you take enough OSRAM
will no doubt deliver directly.
6) They claim the sensor is for auto applications (among others), but why
a particularly good approximation to the sensitivity curve of the eye is
required escapes me. But why ask, if the device meets our needs and desires.
Bob
From: rolandberry@hotmail.com (RolandRB)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Noblex 150 resolution at infinity
Date: 3 May 2004
hemi4268@aol.com (Hemi4268) wrote
> > So, on the fovea with an eye lens with effective
> >focal length of 17mm the resolution in line pairs per millimeter on
> >the cones will be...
> >
> >(254/17)*8 = 135 lp/mm
> >
> >Is this for 20/20 vision?
>
> Sure 135 l/mm might be projected to the back of the eye but only 8 l/mm is
> being picked up.
>
> Same issue with a Nikon loaded with tri-x film. At f-8, 250 l/mm is being
> projected on the film but the film really only picks up about 40 l/mm of the
> 250 l/mm.
>
> Larry
This is on-cone resolution. You see it, right? If you are looking at 8
line pairs per mm ten inches away then you must have an image on the
fovea with an on-cone resolution of 135 lp/mm. That is where the image
is, is it not? On-cone, I stress, because this is what you are
actually seeing.
From: mpate@oscintl.com (Michael Pate)
Newsgroups: sci.optics
Subject: Re: Eye model
Date: 15 Jul 2004
"Alex" sikd@mail.ru wrote
> Hi, All
>
> I'm looking for any information on a human eye model suitable for off-axis
> optical calculations .
> I know two variants of the model
> 1) On the OSLO web site .I hope this model is only suitable for on axis
> calculations
> 2) On the Zemax web site. This model is more complicated.
>
> Does any other eye models available in the form suitable for using in an
> optical design programms?
>
> Thanks, Alex
In my notes from Jim Schwiegerling's Visual Optics course at Univ of
Az I have the following eye models for your reference.
Old School Models with spherical surfaces
Gullstrand-Legrand 1924 & 1975
Emsley 1952
More recent models using aspheric surfaces to model the aberrations in
the eye
Lotmar JOSA V61, P1522 1971
Kooijman JOSA V73, P1544 1983
Navarro JOSA A V2, p 1273 1985
Schwiegerling (Arizona Eye Model) 1995 Dissertation you can find the
geometric parts of the model on his website
http://www.optics.arizona.edu/jschwieg/
Some other book references on the eye are:
Optics of the Human Eye, Atchison & Smith, Butterworth & Heinemann
publisher 2000
The Eye and Visual Optical Instruments, Smith & Atchison, Cambridge,
1997
Physiological Optics, Shouthall, Dover, 1937
Thanks for putting up the Zemax file, I would have done the same with
these other models but I can seem to find my disc with these files.
Michael Pate
From: West Coast Engineering westcoastengineering@westcoastengineering.com
Newsgroups: sci.optics
Subject: Re: Eye model
Date: Wed, 14 Jul 2004
Hi,
My optical design program, ODP, www.westcoastengineering.com, has two
files HUMEYE01.DAT and HUMEYE02.DAT which are the human eye models
from Mil-141 and the Handbook of Optics.
A DEMO is available to download. The program costs $264.00 and comes
with user support and full source code. No hardware or software keys
are necessary and you can run it on as many PCs as you like, even on
Beowulf clusters.
Updates and users support for additional years is available at a very
reasonable price.
Sincerely,
WESTCOASTENGINEERING
From: "Alex" sikd@mail.ru
Newsgroups: sci.optics
Subject: Re: Eye model
Date: Thu, 15 Jul 2004
"Alex" sikd@mail.ru...
>
> "James R (Jim) Lynch III" jrlynchiii@comcast.net...
> > I have never heard of Pomerantzeff's model eye, so thanks for the reference.
> > Would you please post the ZEMAX prescription on sci.optics?
> >
> > I haven't seen anyone mention the book "Visual Instrumentation" by Pantazis
> > Mouroulis, McGraw-Hill, ISBN 0-07-043561-8, ~$110 delivered in 1999. Chapter
> > 4, "Modeling the Refractive and Neurosensor Systems of the Eye" by Larry N.
> > Thibos and Arthur Bradley discusses the "Indiana Eye" at length and gives
> > and optical prescription for it.
> >
> > James R (Jim) Lynch III
System/Prescription Data
File : C:\WUTemp\Eye_best.zmx
Title: MODEL EYE - Pomerantzeff
Date : THU JUL 15 2004
GENERAL LENS DATA:
Surfaces : 11
Stop : 6
System Aperture : Entrance Pupil Diameter = 3
Glass Catalogs : EYE_BEST SCHOTT
Ray Aiming : Off
Apodization : Uniform, factor = 0.00000E+000
Effective Focal Length : 16.68432 (in air at system temperature and
pressure)
Effective Focal Length : 22.28995 (in image space)
Back Focal Length : 0.117281
Total Track : 33.0804
Image Space F/# : 5.561441
Paraxial Working F/# : 5.561441
Working F/# : 5.52266
Image Space NA : 0.08970187
Object Space NA : 1.5e-010
Stop Radius : 1.326151
Paraxial Image Height : 16.64237
Paraxial Magnification : 0
Entrance Pupil Diameter : 3
Entrance Pupil Position : 12.03759
Exit Pupil Diameter : 2.761188
Exit Pupil Position : -20.3983
Field Type : Angle in degrees
Maximum Field : 45
Primary Wave : 0.5875618
Lens Units : Millimeters
Angular Magnification : 0.8143998
Fields : 9
Field Type: Angle in degrees
# X-Value Y-Value Weight
1 0.000000 0.000000 1.000000
2 0.000000 5.000000 1.000000
3 0.000000 -10.000000 1.000000
4 0.000000 15.000000 1.000000
5 0.000000 -20.000000 1.000000
6 0.000000 25.000000 1.000000
7 0.000000 -30.000000 1.000000
8 0.000000 35.000000 1.000000
9 0.000000 -45.000000 1.000000
Wavelengths : 3
Units: Microns
# Value Weight
1 0.486133 1.000000
2 0.587562 1.000000
3 0.656273 1.000000
SURFACE DATA SUMMARY:
Surf Type Radius Thickness Glass
Diameter Conic
OBJ STANDARD Infinity Infinity
0 0
1 STANDARD Infinity 10
27.07517 0
2 STANDARD 11.7 -1
23.4 0
3 EVENASPH 7.8 0.55 CORNEA
12 0
4 EVENASPH 6.5 0
12 0
5 EVENASPH 6.5 3.05 AQUEOUS
12 0
STO STANDARD 10.2 -5e-008 AQUEOUS
0 0
7 STANDARD 10.2 4 LENS
8 0
8 STANDARD -6 0
8 0
9 STANDARD -6 16.4804 VITREOUS
0 0
10 STANDARD -11.7 0
0 0
IMA STANDARD -11.7 VITREOUS
23.4 0
SURFACE DATA DETAIL:
Surface OBJ : STANDARD
Surface 1 : STANDARD
Surface 2 : STANDARD
Aperture : Circular Aperture
Minimum Radius : 0
Maximum Radius : 11.7
Surface 3 : EVENASPH
Coeff on r 2 : 0
Coeff on r 4 : -0.00019557
Coeff on r 6 : 1.5393e-006
Aperture : Floating Aperture
Maximum Radius : 6
Surface 4 : EVENASPH
Coeff on r 2 : 0
Coeff on r 4 : 2.25e-005
Aperture : Floating Aperture
Maximum Radius : 6
Surface 5 : EVENASPH
Coeff on r 2 : 0
Coeff on r 4 : 2.25e-005
Aperture : Floating Aperture
Maximum Radius : 6
Surface STO : STANDARD
Aperture : Circular Aperture
Minimum Radius : 0
Maximum Radius : 3
Surface 7 : STANDARD
Aperture : Floating Aperture
Maximum Radius : 4
Surface 8 : STANDARD
Aperture : Floating Aperture
Maximum Radius : 4
Surface 9 : STANDARD
Surface 10 : STANDARD
Surface IMA : STANDARD
COATING DEFINITIONS:
EDGE THICKNESS DATA:
Surf Edge
1 21.697859
2 -10.063474
3 1.944775
4 0.000000
5 -0.979160
STO 0.817037
7 1.655099
8 1.527864
9 16.480404
10 -11.697859
IMA 11.697859
INDEX OF REFRACTION DATA:
Surf Glass Temp Pres 0.486133 0.587562 0.656273
0 20.00 1.00 1.00000000 1.00000000 1.00000000
1 20.00 1.00 1.00000000 1.00000000 1.00000000
2 20.00 1.00 1.00000000 1.00000000 1.00000000
3 CORNEA 20.00 1.00 1.38069934 1.37710166 1.37405122
4 20.00 1.00 1.00000000 1.00000000 1.00000000
5 AQUEOUS 20.00 1.00 1.34219136 1.33738065 1.33539337
6 AQUEOUS 20.00 1.00 1.34219136 1.33738065 1.33539337
7 LENS 20.00 1.00 1.42623849 1.41997547 1.41749184
8 20.00 1.00 1.00000000 1.00000000 1.00000000
9 VITREOUS 20.00 1.00 1.34069139 1.33598142 1.33409377
10 20.00 1.00 1.00000000 1.00000000 1.00000000
11 VITREOUS 20.00 1.00 1.34069139 1.33598142 1.33409377
F/# DATA:
F/# calculations consider vignetting factors and ignore surface apertures.
Wavelength: 0.486133 0.587562 0.656273
# Field Tan Sag Tan Sag Tan
Sag
1 0.00 deg: 5.4394 5.4394 5.5227 5.5227 5.5530 5.5530
2 5.00 deg: 5.4459 5.4355 5.5292 5.5186 5.5596 5.5490
3 -10.00 deg: 5.4658 5.4237 5.5493 5.5066 5.5797 5.5369
4 15.00 deg: 5.5007 5.4043 5.5844 5.4868 5.6148 5.5168
5 -20.00 deg: 5.5530 5.3774 5.6371 5.4593 5.6675 5.4891
6 25.00 deg: 5.6262 5.3433 5.7108 5.4244 5.7413 5.4539
7 -30.00 deg: 5.7248 5.3023 5.8102 5.3825 5.8408 5.4116
8 35.00 deg: 5.8547 5.2549 5.9410 5.3340 5.9718 5.3625
9 -45.00 deg: 6.2388 5.1417 6.3275 5.2181 6.3587
5.2456
CARDINAL POINTS:
Object space positions are measured with respect to surface 1.
Image space positions are measured with respect to the image surface.
The index in both the object space and image space is considered.
Object Space Image Space
W = 0.486133
Focal Length : -16.433772 22.032617
Focal Planes : -5.838931 -0.135446
Principal Planes : 10.594841 -22.168063
Anti-Principal Planes : -22.272704 21.897172
Nodal Planes : 16.193686 -16.569218
Anti-Nodal Planes : -27.871549 16.298327
W = 0.587562 (Primary)
Focal Length : -16.684323 22.289946
Focal Planes : -6.089744 0.117281
Principal Planes : 10.594580 -22.172665
Anti-Principal Planes : -22.774067 22.407227
Nodal Planes : 16.200203 -16.567042
Anti-Nodal Planes : -28.379690 16.801604
W = 0.656273
Focal Length : -16.776747 22.381754
Focal Planes : -6.180916 0.208403
Principal Planes : 10.595831 -22.173351
Anti-Principal Planes : -22.957663 22.590157
Nodal Planes : 16.200838 -16.568344
Anti-Nodal Planes : -28.562670 16.985151
From: "Alex" sikd@mail.ru
Newsgroups: sci.optics
Subject: Re: Eye model
Date: Thu, 15 Jul 2004
"James R (Jim) Lynch III" jrlynchiii@comcast.net ...
> I have never heard of Pomerantzeff's model eye, so thanks for the reference.
> Would you please post the ZEMAX prescription on sci.optics?
>
> I haven't seen anyone mention the book "Visual Instrumentation" by Pantazis
> Mouroulis, McGraw-Hill, ISBN 0-07-043561-8, ~$110 delivered in 1999. Chapter
> 4, "Modeling the Refractive and Neurosensor Systems of the Eye" by Larry N.
> Thibos and Arthur Bradley discusses the "Indiana Eye" at length and gives
> and optical prescription for it.
>
> James R (Jim) Lynch III
System/Prescription Data
File : C:\WUTemp\Eye_best.zmx
Title: MODEL EYE - Pomerantzeff
Date : THU JUL 15 2004
GENERAL LENS DATA:
Surfaces : 11
Stop : 6
System Aperture : Entrance Pupil Diameter = 3
Glass Catalogs : EYE_BEST SCHOTT
Ray Aiming : Off
Apodization : Uniform, factor = 0.00000E+000
Effective Focal Length : 16.68432 (in air at system temperature and
pressure)
Effective Focal Length : 22.28995 (in image space)
Back Focal Length : 0.117281
Total Track : 33.0804
Image Space F/# : 5.561441
Paraxial Working F/# : 5.561441
Working F/# : 5.52266
Image Space NA : 0.08970187
Object Space NA : 1.5e-010
Stop Radius : 1.326151
Paraxial Image Height : 16.64237
Paraxial Magnification : 0
Entrance Pupil Diameter : 3
Entrance Pupil Position : 12.03759
Exit Pupil Diameter : 2.761188
Exit Pupil Position : -20.3983
Field Type : Angle in degrees
Maximum Field : 45
Primary Wave : 0.5875618
Lens Units : Millimeters
Angular Magnification : 0.8143998
Fields : 9
Field Type: Angle in degrees
# X-Value Y-Value Weight
1 0.000000 0.000000 1.000000
2 0.000000 5.000000 1.000000
3 0.000000 -10.000000 1.000000
4 0.000000 15.000000 1.000000
5 0.000000 -20.000000 1.000000
6 0.000000 25.000000 1.000000
7 0.000000 -30.000000 1.000000
8 0.000000 35.000000 1.000000
9 0.000000 -45.000000 1.000000
Wavelengths : 3
Units: Microns
# Value Weight
1 0.486133 1.000000
2 0.587562 1.000000
3 0.656273 1.000000
SURFACE DATA SUMMARY:
Surf Type Radius Thickness Glass
Diameter Conic
OBJ STANDARD Infinity Infinity
0 0
1 STANDARD Infinity 10
27.07517 0
2 STANDARD 11.7 -1
23.4 0
3 EVENASPH 7.8 0.55 CORNEA
12 0
4 EVENASPH 6.5 0
12 0
5 EVENASPH 6.5 3.05 AQUEOUS
12 0
STO STANDARD 10.2 -5e-008 AQUEOUS
0 0
7 STANDARD 10.2 4 LENS
8 0
8 STANDARD -6 0
8 0
9 STANDARD -6 16.4804 VITREOUS
0 0
10 STANDARD -11.7 0
0 0
IMA STANDARD -11.7 VITREOUS
23.4 0
SURFACE DATA DETAIL:
Surface OBJ : STANDARD
Surface 1 : STANDARD
Surface 2 : STANDARD
Aperture : Circular Aperture
Minimum Radius : 0
Maximum Radius : 11.7
Surface 3 : EVENASPH
Coeff on r 2 : 0
Coeff on r 4 : -0.00019557
Coeff on r 6 : 1.5393e-006
Aperture : Floating Aperture
Maximum Radius : 6
Surface 4 : EVENASPH
Coeff on r 2 : 0
Coeff on r 4 : 2.25e-005
Aperture : Floating Aperture
Maximum Radius : 6
Surface 5 : EVENASPH
Coeff on r 2 : 0
Coeff on r 4 : 2.25e-005
Aperture : Floating Aperture
Maximum Radius : 6
Surface STO : STANDARD
Aperture : Circular Aperture
Minimum Radius : 0
Maximum Radius : 3
Surface 7 : STANDARD
Aperture : Floating Aperture
Maximum Radius : 4
Surface 8 : STANDARD
Aperture : Floating Aperture
Maximum Radius : 4
Surface 9 : STANDARD
Surface 10 : STANDARD
Surface IMA : STANDARD
COATING DEFINITIONS:
EDGE THICKNESS DATA:
Surf Edge
1 21.697859
2 -10.063474
3 1.944775
4 0.000000
5 -0.979160
STO 0.817037
7 1.655099
8 1.527864
9 16.480404
10 -11.697859
IMA 11.697859
INDEX OF REFRACTION DATA:
Surf Glass Temp Pres 0.486133 0.587562 0.656273
0 20.00 1.00 1.00000000 1.00000000 1.00000000
1 20.00 1.00 1.00000000 1.00000000 1.00000000
2 20.00 1.00 1.00000000 1.00000000 1.00000000
3 CORNEA 20.00 1.00 1.38069934 1.37710166 1.37405122
4 20.00 1.00 1.00000000 1.00000000 1.00000000
5 AQUEOUS 20.00 1.00 1.34219136 1.33738065 1.33539337
6 AQUEOUS 20.00 1.00 1.34219136 1.33738065 1.33539337
7 LENS 20.00 1.00 1.42623849 1.41997547 1.41749184
8 20.00 1.00 1.00000000 1.00000000 1.00000000
9 VITREOUS 20.00 1.00 1.34069139 1.33598142 1.33409377
10 20.00 1.00 1.00000000 1.00000000 1.00000000
11 VITREOUS 20.00 1.00 1.34069139 1.33598142 1.33409377
F/# DATA:
F/# calculations consider vignetting factors and ignore surface apertures.
Wavelength: 0.486133 0.587562
0.656273
# Field Tan Sag Tan Sag Tan
Sag
1 0.00 deg: 5.4394 5.4394 5.5227 5.5227 5.5530 5.5530
2 5.00 deg: 5.4459 5.4355 5.5292 5.5186 5.5596 5.5490
3 -10.00 deg: 5.4658 5.4237 5.5493 5.5066 5.5797 5.5369
4 15.00 deg: 5.5007 5.4043 5.5844 5.4868 5.6148 5.5168
5 -20.00 deg: 5.5530 5.3774 5.6371 5.4593 5.6675 5.4891
6 25.00 deg: 5.6262 5.3433 5.7108 5.4244 5.7413 5.4539
7 -30.00 deg: 5.7248 5.3023 5.8102 5.3825 5.8408 5.4116
8 35.00 deg: 5.8547 5.2549 5.9410 5.3340 5.9718 5.3625
9 -45.00 deg: 6.2388 5.1417 6.3275 5.2181 6.3587 5.2456
CARDINAL POINTS:
Object space positions are measured with respect to surface 1.
Image space positions are measured with respect to the image surface.
The index in both the object space and image space is considered.
Object Space Image Space
W = 0.486133
Focal Length : -16.433772 22.032617
Focal Planes : -5.838931 -0.135446
Principal Planes : 10.594841 -22.168063
Anti-Principal Planes : -22.272704 21.897172
Nodal Planes : 16.193686 -16.569218
Anti-Nodal Planes : -27.871549 16.298327
W = 0.587562 (Primary)
Focal Length : -16.684323 22.289946
Focal Planes : -6.089744 0.117281
Principal Planes : 10.594580 -22.172665
Anti-Principal Planes : -22.774067 22.407227
Nodal Planes : 16.200203 -16.567042
Anti-Nodal Planes : -28.379690 16.801604
W = 0.656273
Focal Length : -16.776747 22.381754
Focal Planes : -6.180916 0.208403
Principal Planes : 10.595831 -22.173351
Anti-Principal Planes : -22.957663 22.590157
Nodal Planes : 16.200838 -16.568344
Anti-Nodal Planes : -28.562670 16.985151
From: Mike Jones jonesmi@airmail.net
Newsgroups: sci.optics
Subject: Re: Eye model
Date: Mon, 12 Jul 2004
Alex wrote:
> Hi, All
>
> I'm looking for any information on a human eye model suitable for off-axis
> optical calculations .
> I know two variants of the model
> 1) On the OSLO web site .I hope this model is only suitable for on axis
> calculations
> 2) On the Zemax web site. This model is more complicated.
>
> Does any other eye models available in the form suitable for using in an
> optical design programms?
>
> Thanks, Alex
I use Pomerantzeff's model in Zemax. It includes aspherics and changes in
asphericity with accomodation. One reference:
Pomerantzeff, O., Fish, H., Govignon, J. and Schepens, C. L. "Wide angle
optical model of the human eye." Ann Ophthalmol 3(8): 815-9,1971.
While at the library search JOSA - there are several different eye models.
Pomerantzeff's model is one of the most accurate (statistically, anyway).
Mike
Date: Mon, 12 Jul 2004
From: Jim Palmer jpalmer@dakotacom.net
Newsgroups: sci.optics
Subject: Re: Eye model
...
The MIL-HDBK-141 standard military eyeball can be found at
http://www.azmackes.net/astronomy/mil_hdbk_141/. Look in chapter 4. jmp
Subject: Re: Eye model
From: Repeating Rifle SalmonEgg@sbcglobal.net
Newsgroups: sci.optics
Date: Mon, 12 Jul 2004
...
I am not a lens designer and have not used any of the various design
programs.
Schematic eyes are presented in the now famous MIL-HDBK-141 and in the OSA
Handbook of Optics. The OSA publication also suggests folly in trying to
make a more accurate but ultimately unattainable model.
Of course the schematic eye requires YOU to enter the optical description
into your design program.
Bill
From: "jjs" john@mychain.stafford.net
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Light Meter Spectral Response
Date: Sun, 11 Jul 2004
May I suggest a couple sources regarding human vision and color perception?
It is important because looking at film response curves presumes a knowledge
of human color vision. We have some very interesting perceptual
peculiarities, for example the inability regardless of training to
distinguish certain colors in juxtaposition, a profound confusion of
"violet"/"purple", red and blue mixtures and our response to luminance skews
impressions such that we cannot see certain colors. So when one looks at a
chart of spectral responses it might help to try to look at an actual scene
and study the assumptions, misinterpretations we might be making.
Please see "Vision and Art: the Biology of Human Vision" by Margaret
Livingston
For examples of the colors we cannot distinguisn in justaposition, see "Art
and Visual Perception" by Rudolph Arnheim.
B&W; photography _is_ color photography.
jjs
From: rolandberry@hotmail.com (RolandRB)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Noblex 150 resolution at infinity
Date: 2 May 2004
hemi4268@aol.com (Hemi4268) wrote
> >8 lines per millimeter on the fovea? No chance. 8 lines per millimeter
> >at a standard distance, perhaps. Can you give me a URL where I can
> >check on this figure of 8 lines per millimeter?
>
> Just about every good manual on printing, something that people have been doing
> since the 1500's, will have notations that 8 l/mm is the standard. Lacking
> that, try the SPSE manual.
>
> Standard is 8 l/mm at 10 inches view distance.
>
> Larry
As I thought. At a standard distance. Not very useful if quoted
without the distance. So, on the fovea with an eye lens with effective
focal length of 17mm the resolution in line pairs per millimeter on
the cones will be...
(254/17)*8 = 135 lp/mm
Is this for 20/20 vision? I suspect it is. For reading the bottom line
(the one above the line they cross out) of an eye chart? I have had my
eyes tested on a regular basis. Before I was 8 years old I used to
read out the makers name right at the bottom of the chart. I had lost
the ability to do that when I was 9 or 10.
Also which ethnic group is this? I know for Australian aboriginees it
is much higher. You could put another 4 lines below the one they
usually cross out and they can read them if their eyes are good.
The cones of the fovea have a diameter of 1.5 microns on average (this
varies a lot between ethnic groups). So you have a theoretical line
pair in 3 microns. So in line pairs per millimeter you have a
theoretical 333 lp/mm. It won't be quite as high as this since they
are colour cones. And I stress this varies between ethnic groups.
There was a famous Australian aboriginee who could draw a detailed map
of the moon and drew Venus as a crescent. I can not find a URL for
this. If true then that would put the maximum resolving power of the
eye much higher.
From: hemi4268@aol.com (Hemi4268)
Newsgroups: rec.photo.equipment.medium-format
Date: 02 May 2004
Subject: Re: Noblex 150 resolution at infinity
>8 lines per millimeter on the fovea? No chance. 8 lines per millimeter
>at a standard distance, perhaps. Can you give me a URL where I can
>check on this figure of 8 lines per millimeter?
Just about every good manual on printing, something that people have been doing
since the 1500's, will have notations that 8 l/mm is the standard. Lacking
that, try the SPSE manual.
Standard is 8 l/mm at 10 inches view distance.
Larry
From: rolandberry@hotmail.com (RolandRB)
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Noblex 150 resolution at infinity
Date: 2 May 2004
hemi4268@aol.com (Hemi4268) wrote
> >You will find that the resolving power of the human eye is very high.
>
> Actually the resolving power of the eye is well documented. It's 8 lines per millmeter.
>
> Larry
8 lines per millimeter on the fovea? No chance. 8 lines per millimeter
at a standard distance, perhaps. Can you give me a URL where I can
check on this figure of 8 lines per millimeter? I have to wonder
whether they are measuring something else altogether. For vision on
the fovea I would estimate about 200 lines pairs per millimeter
on-cone resolution is possible for people with excellent vision. I am
looking at my computer screen at the moment and I think I can easily
resolve 5 line pairs per millimeter at 300mm away (1 feet). The focal
length of the eye is 17mm so I make that...
(300/17)*5 = 93 lp/mm
This is on the cones there. And that was a very rough check.
From: hemi4268@aol.com (Hemi4268)
Newsgroups: rec.photo.equipment.medium-format
Date: 01 May 2004
Subject: Re: horizon 202 resolution Re: Noblex 150 resolution at infinity
> I can bore everybody with an actual calculation of shake
>and the effect on lens (not film) resolution but I haven't got round
>to doing the maths yet. But I aim to do this in the future -- so
>"sorry everybody".
These calculations have alread been done. The secret is to figure out shake in
milliradens per second. Then figure out image motion vs focal length and
resolution. Last is to calculate where in the sine curve the photographs are
most likely to be imaged.
The results can be read out in chances in 10. In other words with a 35mm lens
at 1/35 of a second you have 5 chances out of ten to at least get one image
with no motion. So several photographs will be enough.
Change the lens to 135mm with the same 1/35 of a second and the chances go down
to 1 in 10. In other words, you must take 10 images to get one that is motion
free.
Larry
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