I recently got a Berthiot Perigraphe 90/F14 for my 5x7 format. But I don't how to read the aperture setting. It has a dial set aperture setting with marks "14, 20, ..." I don't know how to convert them to normal aperture reading, such as "16, 22, 32, 45, ..." Would like to seek some help in the forum.
You list 14, 20. What are the next two numbers in sequence? I suspect they are 28, 40. If so, they are f-numbers using a different scale.
You are correct. The next two are 28, 40. But I can not read for the last one, which is probably 56. How to use the f-number scale correctly and linked to our current light meter readings?
I found I posted in the wrong segment. I should re-posted onto the "lenses and accessories" section.
The numbers really are f-numbers. Berthiot preferred basing the scale on f/10 rather than the more common (to us now) based on f/1. some others went to f/100, so that stops were marked 13, 18, 25, 35, 50, 70, 100...
So take your f/14 to really be f/14, or about half a stop more open than f/16.
Last edited by Ole Tjugen; 8-Jun-2010 at 10:42. Reason: spellling
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