Lens evaluation using instant film

[Bill Brady]

Howdy folks,

Can any meaningful evaluation be made of LF lenses using instant film. I know, for example that some Polaroid material resolution is only about 20 lp/mm. I can't find any info on Fuji film though.

I recently came into possesion of a fair quantity of Fuji 100C that expires in a coupla months. Normally I would use sheet film and my Edmunds USAF style test poster.

In several cases I have 2 lenses of similar F/L and I need a quick way of determining which to keep and which to sell.

All help will be appreciated. Thanks!

[Emmanuel BIGLER]

Well, as you mention, only 20 lp/mm on a Polaroid positive print is a bit short for discriminating a top-class LF lens from a good ol' vintage lens suitable for contact prints. A minimum of 30-40 lp/mm is what you may expect from many vintage and, of course, modern LF lenses.
However you may try a pos/neg polaroid instant film (type 665 is being phased out but type 55 in 4"x5" is still manufactured) that will yield an excellent fine-grain negative.
But this is more expensive that a handy stock of "expired" positives...

[Jim Rhoades]

They say that the film used in type 55 is Panatomic-X. In any case it's a real good negative and should work for testing.

[Bill Brady]

Thanks Guys,

I have some PN55. But hate to use that due to the cost.

Remember, I only want to generally compare lenses of similar focal length, such as a 150mm Symmar and a 150 Apo Symmar where the Apo Symmar is a bit more "used" in appearance and has a small amounts of seperation at the edge. I also have an old Angulon and the slower version of the Super Angulon and there would be no need of comparison if the Angulon was not so much smaller/lighter (this is my field kit).

So I am not testing absolute resolution per se, but shouldn't I be able to get an idea of contrast, coverage, exposure accuracy and distortions? Or am I about to waste the 100C?

[Christopher Perez]

I suggest there's no way getting around shooting _some_ film. Pick a difficult aperture (say, f/11) and assume f/16 and f/22 will be diffraction limited. Pick a scene with decent contrast. Then slip your film after processing under a microscope at 160x magnification. Differences will be obvious.

Quick? Maybe not. Cheap? Potentially.