Many photographers wonder why they can't use their 35mm SLR lenses with
adapters in place of expensive medium format lenses. The short answer is
that few 35mm lenses have enough coverage to cover 6x4.5cm or 6x6cm images.
But there are some that do, making such finds an exciting and low cost way
to "hack" lenses between formats. Moreover, you can build your own camera, including swing lens and
panoramic cameras, often using 35mm SLR
lenses on both 35mm and even medium format panoramic cameras. So learning
more about 35mm lens converage and potentials can have benefits to lens hacking experimenters and homebrewers.
Most 35mm lenses are designed to cover the 24x36mm frame, which
corresponds to a triangle whose longest side is 43mm. So a lens capable
of covering 43.2mm is the minimum coverage needed. By contrast, a 6x4.5cm
lens has a diagonal of circa 72mm, while a 6x6cm (really 56mm x 56mm)
needs 79.2mm.
In general, these figures are for wide open apertures, since lens
coverage improves somewhat as we stop down the lens (circa 10-15-20% or
more, depending on the design). Similarly, these figures are for objects
at infinity, as lens coverage increases hugely when lenses are used for
closeup work (circa 100-300%).
On our Homebrew Lenses page, we describe how
you can build a simple lens coverage evaluator. The basic idea is simply
a box with a bottom covered with ground glass and a top with a hole to
mount the lens (or a reverse-T mount in a deluxe design). Simply slide
the box cover out to get infinity focus, and observe the lens coverage
directly (with a dark-cloth if needed) using a millimeter scale. This
technique doesn't give you exact values, but it does make it easy to sort
through a box of low cost surplus lenses on a dealer's table to find the
best candidates for lens hacking experiments. Note that the presence
of light guards at the rear of some telephoto lenses is a good
indicator of potentially excess coverage.
You can also mount the lens in a temporary (cardboard) mounting on a view
camera, and shoot an actual exposure. Use your hat and neutral density
filters as a replacement for a shutter, or use a packard shutter or focal
plane shutter view camera with these non-leaf shutter 35mm lenses.
Standard (non-collapsed) telephoto designs often perform surprisingly
well when adapted from 35mm to 6x4.5cm and even 6x6cm use. See examples of
500mm f/8 glass lens adaptations for one
35mm lens that works nicely on 6x6cm!
Similarly, many very wide 35mm lenses (such as 24mm nikkor) work well
enough to cover a thin (typically 3mm) slit used in slit cameras on
either 35mm or 120 rollfilm panoramic cameras. That is very handy, as a
true ultrawide lens on 6x4.5cm or 6x6cm for a panoramic camera would be
much more expensive for similar quality imaging.
In summary, there are lots of opportunities for using 35mm SLR lenses in
specialty applications (swing lens cameras) and even with larger formats
(telephotos on 6x6cm) that defy conventional wisdom about the coverage of
35mm lenses limitations. Unfortunately, since lens coverage data is not
supplied with or published for 35mm lenses, you simply have to test it
out on your particular lenses...
Date: Thu, 13 Jan 2000
From: "M. Denis Hill" denis@area360.com
To: panorama-l@sci.monash.edu.au
Subject: RE: Nikkor coverage
> M. Denis Hill wrote: > >I meant to say, "Nikkor lenses as short as 24mm cover 120/220 film." > > Are you really sure about this? I have some Niklkors and I have the 2 PC > Nikkors. They will cover 56mm but evenly (Nikon suggests that > when shifting > on the long axis of the film to not shift more than 8mm because there is > fall off). None of the other Nikkors (except the view camera lenses) will > cover anywhere near this amount. Or so it seems to me. > > Joe McCary
My personal experience with a 35mm pc Nikkor agrees with yours, you can't
use the full 11mm of available shift.
I have personally determined that the 18mm Nikkor only covers about 46mm.
I understand from the experience of others that a 24mm Nikkor will cover
55mm, but have not had the opportunity to confirm this. Note that LeLostic
implies that the 24mm lens covers 55mm in his technical notes on his
ScanTech cameras at
http://perso.wanadoo.fr/panorama/francais/fiche_tech.htm.
Denis
[Ed. note: see Lens Variations
Pages for more on lens variability]
Date: Fri, 14 Jan 2000
From: Robert Erickson cirkut8@yahoo.com
To: panorama-l@sci.monash.edu.au
Subject: Re: Nikkor coverage
Take it as a fact that a 24mm Nikkor lens coverage
will vary from year to year.
I have experence building LarScan rotational cameras
with many different brands and models of 35mm format
lenses. I have learned the hard way that the coverage
on 120/220 film using the same focal length lens will
vary a lot, even using the same focal length lens from
the same manufacturer!
The beauty of using stock lenses is that you can build
the camera with any stock lens and then later find the
model with the greatest coverage.
Bob
....
Date: Fri, 14 Jan 2000
From: Willem-Jan Markerink w.j.markerink@a1.nl
To: panorama-l@sci.monash.edu.au
Subject: Re: Nikkor coverage
> "M. Denis Hill" wrote: > > > > The camera is indeed appealing. In prior discussions on this topic, I > > learned that some lenses for 35mm cameras cover substantially less image > > area than Nikkors. As I recall, lenses as short as 24mm cover 120/220 film. > > I'm not certain about Nikkor 20s, but my 18mm only covered about 45mm. > > The 28mm and 35mm Nikkor PC lenses cover a 120 (56mm) slit > Also the Olympus and Canon 24mm shift lenses
EOS does 58mm IIRC....:-))
(stopped down probably more (red area on both shift & tilt))
--
Bye,
Willem-Jan Markerink
w.j.markerink@a1.nl
[note: 'a-one' & 'en-el'!]