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difference between a large aperture and a small one during enlarging

Oskar Kostecki , Mar 09, 2008; 12:32 p.m.

Hey, this is sort of a begginer question, but i'm wondering, based on the reciprocity rule, if i enlarge at f/4 for 10 seconds, and another print at f/8 for 5 seconds, they should be the same, yes? so, what is the difference? is the contrast greater, the bigger your exposure? i was just reading about the reciprocity rule in this book, but it doesn't further explain, so i came here. maybe i'm not really understanding, in which case i'd be delighted with some assistance. thanks, oskar


Stephen Lewis , Mar 09, 2008; 12:52 p.m.

NO. You have 2 f stops of difference, so your times should be increased by a factor of 4. But further you have things backwards. F4 means more light than F8 (by a factor of 4). If you wanted equivalent prints you would print f4 for 10 seconds and f8 for 40 seconds. Contrast relates to a variety of items...not really to the degree of enlargement. It is related to the range of density range of your negative, the type of paper you are using, and the developer you are using. I suggest you read Ansel Adams' The Negative and The Print. You are missing some of the very basic information, and these books will help you get a better overall grasp of the issues involved. The reciprocity rule has limited application for most people in both in exposing a negative and printing.

Michael Darnton , Mar 09, 2008; 02:02 p.m.

There is one big difference between f4 and f8, and that is that especially with an enlarging lens you want to find the lens' optimum opening and try to stay in that neighborhood. For most enlarging lenses that would be around f5.6-f8, and not f4, by which time the corners won't be brought into sharpness, or f11, by which time most lenses will be turning sharp grains in the film into mush on the paper.

Frank Schifano , Mar 09, 2008; 09:57 p.m.

What Michael wrote is true up to a point. In practice though, the differences with a good 6 element enlarging lens from one of the major players in the field, will not be noticeable in modest enlargements. Artifacts introduced by lens aberrations may become noticeable in enlargements of greater magnification IF you stick your nose in the print. View it from a normal viewing distance (2x the diagonal of the print is considered normal if I recall correctly) and the argument is moot.

Vlad Soare , Mar 10, 2008; 05:56 a.m.

I wouldn't rely on reciprocity, since in my experience the reciprocity of photographic papers is very poor to say the least. Your calculations will give you a starting point, but they won't save you from testing.

Kevin Bourque , Mar 10, 2008; 08:31 a.m.

Don't worry about reciprocity so much as diffraction. You really do lose sharpness at tiny apertures.

Focus on a good grainy negative (with some kind of magnifier) with the lens wide open and then click it closed one stop at a time. It'll get a little sharper for a few clicks and by the time you get to the smallest opening the grain will have completely disappeared.

Dave Wilson , Mar 14, 2008; 06:41 p.m.

I would also reccomend an enlarger exposure meter, just a simple one saves paper and hassels to an extent. Yes, true a really good lens will print wide open, I prefer to stop down about two stops on any lens, they get a little crisper. Like all lenses, stopping all the way down, like already mentioned can cause diffraction, not so good.

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