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Mirror Vision
Project
On my Weird Lenses Pages, I highlight
the unique Spiratone "bird's eye view lens" which takes in 220
degrees. Now you can buy a prime Nikon fisheye lens which takes in 220
degrees too - enabling it to take in areas behind the front hemisphere of
the lens (which is huge and bends backwards to get this rearward
view). But the prime lens would cost as much as many budget new cars. For
the price of a couple of pizzas, you can buy the Spiratone bird's eye lens
(used market only).
Like its high priced competitor, the Spiratone bird's eye lens takes in
220 degrees too. But it does so thanks to a low cost reflecting metal
sphere. The sphere is suspended in front of the camera lens inside a clear
plastic cylinder several inches in diameter. The bottom of this plastic
cylinder has a closeup or diopter lens
(typically +10 diopters for a 4 inch or 100mm setup). A filter ring mount
enables this tube to screw into the filter ring on your camera (possibly
using an adapter from the standard size used (often 52mm)). So your camera
is taking a closeup photo of the world as reflected back to it from a
reflecting metal sphere. Make sense?
The edges of the sphere have a compressed but clear view of up to
220 degrees, just like the high priced nikkor. Since the metal sphere
is reflecting the scene back to the camera's regular lens, the camera is
inevitably in the center of every picture. So you can tell which photos
were taken with the low cost adapter (camera in center of picture) versus
the hopefully rented high priced Nikkor images (no camera in center of
picture, but lots of photographer's toes and noses in the side imagery!).
Next time you go shopping for Christmas
tree ornaments, take a close look at those thin glass spheres in the
box. If you move the spheres so they are in contact, you may notice a
curious optical phenomenon at the edges. The spheres darken where the
reflection is being bounced back and forth between the touching spheres.
Light is reflected back and forth so many times that it gets absorbed and
hence darkens these edges. Nifty, huh?
If you have a close focusing macro lens, you can probably use a simple
metal sphere to produce a reflected scene with enormous coverage. See our
fisheye pages for related notes. Besides
metal or silvered reflecting spheres, you can also use various security
mirrors to get similarly distorted ultrawide coverage photographs. Getting
such coverage with a prime optic might be impossible, but in any case the
cost would be very high for a prime fisheye optic.
A new wrinkle on this old technique is now introduced by the
computer. Using various panoramic software, the extreme distortion of such
fisheye photos can be removed by the computer. The resulting image is an
ultrawide, relatively undistorted image covering a tremendous field of
view. Wow! For very little cost and some free software you can scan and
straighten out your distorted fisheye images into passable rectilinear
images (see our
panoramic pages for links to free software).
The following postings provide some insight into sources for such mirrored
spheres, and things you can do with them too. Our thanks to all those who
have contributed these ideas and suggestions on these various public
forums!
From Panoramic Mailing List:
Date: Thu, 06 Jul 2000
From: Charles Stumpfel stumpfel@arl.army.mil
Subject: light gathering vs diameter of reflecting spheres
Knowing next to nothing ---
I'd like to understand the how reflectors might be used for panoramic
imaging.
A video camera was set up viewing a 3/4" diameter chrome steel ball
bearing so that the ball's image filled the camera's vertical FOV.
How does the diameter of a reflecting sphere affects light gathering? In
other words does a larger diameter ball bearing, imaged to still fill the
FOV, cause more light to fall in the image? I'm ordering a 1" diameter
ball to find out the quick way. [The 1 " diameter ball is supplied by
Small Parts, Inc. in Miami FL]
Does anyone know of a supplier for precision ball bearings larger than 1"
in diameter? Any specifics on other commercially available curved
reflectors other than ball bearings would also be of interest.
Chas Stumpfel
From Panoramic Mailing List:
Date: Thu, 06 Jul 2000
From: Nathan Myhrvold nathanm@MICROSOFT.com
Subject: RE: light gathering vs diameter of reflecting spheres
Weather reseacher use "whole sky cameras" to record cloud cover. These are
basically an ordinary camera lens pointed at a mirrored sphere - those I
have seen are approx 8-12 inches in diameter. The camera appears in the
picture, of course, and the view is quite distorted.
Nathan
> -----Original Message----- > From: Charles Stumpfel [mailto:stumpfel@arl.army.mil] > Sent: Thursday, July 06, 2000 > To: Panorama-l@sci.monash.edu.au > Subject: light gathering vs diameter of reflecting spheres > > > Knowing next to nothing --- > > I'd like to understand the how reflectors might be used for panoramic > imaging. > > A video camera was set up viewing a 3/4" diameter chrome steel ball > bearing so that the ball's image filled the camera's vertical FOV. > > How does the diameter of a reflecting sphere affects light > gathering? In > other words does a larger diameter ball bearing, imaged to > still fill the > FOV, cause more light to fall in the image? I'm ordering a > 1" diameter > ball to find out the quick way. [The 1 " diameter ball is supplied by > Small Parts, Inc. in Miami FL] > > Does anyone know of a supplier for precision ball bearings > larger than 1" > in diameter? Any specifics on other commercially available curved > reflectors other than ball bearings would also be of interest. > > > Chas Stumpfel >
From Panoramic Mailing List:
Date: Thu, 06 Jul 2000
From: Helmut Dersch der@fh-furtwangen.de
Subject: Re: light gathering vs diameter of reflecting spheres
Charles Stumpfel wrote:
> I'd like to understand the how reflectors might be used for panoramic > imaging.
Images from convex spherical mirrors can be remapped to
the standard cylindrical panorama formats using my free
software 'Panorama Tools'. See my website for examples
of Macropanoramas using this technique.
Try also Versacorp, BeHere, and Cyclovision for commercial
systems.
> How does the diameter of a reflecting sphere affects light gathering? > > Does anyone know of a supplier for precision ball bearings larger than 1" > in diameter?
Ball bearings don't have optical grade sufaces. Much better results
can be obtained by using 'real' spherical mirrors. These are
manufactured using glas lenses, which are coated with aluminum.
Most lens manufacturers sell almost any size and shape, eg
Newport and Spindler&Hoyer;, where I got mine from.
Helmut Dersch
-------------------------------------
Spherical Panoramas, Macro Panoramas,
Free Panorama Software,
Mailing List "Immersive Imaging":
http://www.fh-furtwangen.de/~dersch
From Panoramic Mailing List;
Date: Thu, 06 Jul 2000
From: MIKE GRACE amazing50@hotmail.com
Subject: RE: light gathering vs diameter of reflecting spheres
Does anyone know of a supplier for precision ball bearings larger than 1"
in diameter? Any specifics on other commercially available curved
reflectors other than ball bearings would also be of interest.
Chas Stumpfel
Safety supply companies sell all sorts of curved reflectors made of plastic.
They are used in factories to improve visibility and are quite good
optically.
Mike Grace
amazing50@bigfoot.com
http://www.geocities.com/Paris/LeftBank/3923 /
From Panoramic Mailing List:
Date: Thu, 06 Jul 2000
From: Alan Zinn azinn@netbox.com
Subject: Re: light gathering vs diameter of reflecting spheres
you wrote:
>Knowing next to nothing --- > >I'd like to understand the how reflectors might be used for panoramic >imaging. > >A video camera was set up viewing a 3/4" diameter chrome steel ball >bearing so that the ball's image filled the camera's vertical FOV. > >How does the diameter of a reflecting sphere affects light gathering? In >other words does a larger diameter ball bearing, imaged to still fill the >FOV, cause more light to fall in the image? I'm ordering a 1" diameter >ball to find out the quick way. [The 1 " diameter ball is supplied by >Small Parts, Inc. in Miami FL] > >Does anyone know of a supplier for precision ball bearings larger than 1" >in diameter? Any specifics on other commercially available curved >reflectors other than ball bearings would also be of interest. > > >Chas Stumpfel >
Chas,
Maybe a dumb question but why not xmas balls? Also there are vacuum plated
"chrome" spheres at craft stores. I have some I used for a photo project
(not pans).
AZ
New Minneapols pans 6/30/00
Lookaround Panoramic Camera and Gallery:
http://www.geocities.com/SoHo/Gallery/8874/
From Panoramic Mailing List:
Date: Fri, 07 Jul 2000
From: Charles Stumpfel stumpfel@arl.army.mil
Subject: Re: light gathering vs diameter of reflecting spheres
My original message (bottom) on the acrylic hemispheres with 9" dia. at
$30-40 was from memory and likely wrong since I could not find it again.
Badger has 9" dia stainless hemispheres but no price was listed. They
also have larger diameter acrylic hemispheres.
Sun-Rise has some prices on larger spheres but they are more than the
$30-40.
Chas Stumpfel
This company supplies hemispherical mirrors for safety applications:
Badger Merchandise Service
1-800-771-4972
(phone message says they are closed until Monday)
http://www.badgermart.com/sentinel.html
----------------------------------------------------------------------------
Another company was
http://www.sun-rise.com/mirrors/621884.001.html
----------------------------------------------------------------------------
Probably found by searching convex mirror.......safety mirror......whole sky mirror.... all sky mirror.
Sun-Rise states these acrylic hemispherical mirrors are coated on the inner side - not front surface.
I think they are sold mostly for viewing with the eye.
For some applications there might be objectionable reflections, especially of strong sources, from the uncoated acrylic surface. ??
Chas Stumpfel
From Panoramic Mailing List:
Date: Fri, 07 Jul 2000
From: Alan Zinn azinn@netbox.com
Subject: Re: light gathering vs diameter of reflecting spheres
you wrote:
>Spiratone made a 220 degree bird's eye lens for circa $20 US; it used a >lens thread mount, clear plastic tube to hold an aluminized spheroidal >surface, and a closeup diopter lens to bring it into focus. Folks >suggested you could do the same thing with a +10 diopter lens, a silver >xmas tree bulb (epoxied inside for strength?), and a clear PVC tube and >broken out filter epoxied to the inside of the PVC tube. > >see http://www.tbk.de/news/birdeye1.htm for somewhat similar newer item >and http://www.smu.edu/~rmonagha/third/weird.html Wierd Lenses pages >and ~rmonagha/bronfe.html fisheye pages on related low cost options... > >regards bobm
Don't know if this will help but I was just in a Michaels craft store and
saw a 12in. mirrored glass "Gazing sphere" for $24.00 US. It is for making
lawn ornaments. It looked very nice. I wouldn't think too fancy a sphere
would be necessary for VDT display. I presume the camera is edited out.
AZ
New Minneapols pans 6/30/00
Lookaround Panoramic Camera and Gallery:
http://www.geocities.com/SoHo/Gallery/8874/
Email suggestions, updates,
comments, links, and glitches to fix - Thanks!