View Full Version : Process camera lens question

22-Feb-2015, 16:00
OK, I see process lenses all the time with this scale/pointer on them, but I can't figure out what it would be used for. The outer ring is clearly the aperture of the lens, but what do the numbers on the inner rings represent?

I've searched archives here, and Google for the last hour, but haven't found anything (probably because I don't know what terms to use, as I was always in editorial, not in the press room, when I worked for a newspaper).

This is purely for my own curiosity, I'm not planning to make offset printing plates anytime soon! Clearly, you wouldn't use the guide for regular large format photos with a process lens.


22-Feb-2015, 16:56
That scale is meant to provide a short cut to determining the effective f number based on the reproduction ratio that is being used, since a process camera may be used at distances much closer than normal pictorial photography. While not explaining the scale in depth, this gives an explanation of the problem to be addressed in determining the effective f stop in a process camera setup, from the Apo-Nikkor brochure:


23-Feb-2015, 09:13
I aee, so it's kind of like a way to automatically calculate bellows extension, but based on magnification, not bellows length. Got it!