View Full Version : periskop and uncorrected lens

Sven Schroder
15-Feb-2007, 06:10
Hi all

I recently picked up a bunch of lens, a mixture of named and unamed Aplanats etc. amongst them are some that appear to be two single meniscus elements mounted about a central stop i.e periskop. They are unamed, reflections match my vademecum set and on the groundglass they are rather funky with chromatic abberations like red edges to the out of focus highlights and some soft glow as well. There is one around 210 f7(waterhouse) and a 270 ish f8 (iris dia) narrow coverage not covering 10x8 at infinity. So in use do I have to adjust for chemical focus? Do I have to use ortho/blue sensitive film? I intend to utilize them for still life/studio. Also finally picked up a Adjustable landscape lens by A Darlot/pulligny which is bit more complex in use. I don't have alot of time at the moument but want to explore the my funky side in the studio.

Ole Tjugen
15-Feb-2007, 06:45
The "Chemical focus" correction was necessary in the days when plates were only sensitive to UV and shortwave blue light. Since the eye has greatest sensitivity in green/yellow, it looks sharpest to us when that range is in focus, while the film image will be sharpest when UV is in focus.

With modern films this correction is no longer that necessary. Using a strong coloured filter will improve sharpness a lot, but always focus with the filter in place. Note that the focal length will be different with a blue filter compared to a red filter!

If you want to use the "whole smear", try a light yellow (or "skylight") filter to remove the UV component.

BTW - they can be surprisingly sharp under the right conditions. :)

Sven Schroder
15-Feb-2007, 07:40
Hi Ole

Thanks for the tips, the funk begins to drop off within a stop or two, but I have sharp lenses for those conditions. The OOF is fantasic/crazy on the 210 F7 ( waterhouse) and I should be able to get on quicker now.

Paul Fitzgerald
16-Feb-2007, 07:49
Thank you Ole,

Sven and Ole,

I have 1 lens that shows a focus shift from visual to film focus, 20mm worth of shift. That was tested on color-blind process film, Kodak's Aero duplicating 2421. Tested the same lens on ERA pan film last night, no focus shift is detectable from visual. No filter.

Thanks again, it's the 'Magic lens' and it's been sitting too long in the closet.