F-Stop Printing Calculator - support page
How it works
The F-Stop Printing Calculator assumes you need to establish 1/4 stop increments (+ or – up to 3/4) of the base time you have entered and, either generate a new time, or an increment of an f-stop if you are burning in. It can also be used to make a test strip with smaller increments. The basic way to work would be to generate a test strip with intervals one f-stop apart (say 4, 8, 16, 32 seconds). If you think a correct exposure is half way between two that you have, enter the lower time in the F-Stop Printing Calculator, click GO! and the calculator will tell you the new time to use. So, if 8 seconds were too light, and 16 seconds too dark, the half way point is 11.3 seconds. You have the option of using 1/4 stops if you think it is not exactly halfway.
The web based calculator will do the maths, but the app gives you the whole thing in your hand, with a red light mode for use in the darkroom. Click on the Digitaltruth Photo icon for instructions, system requirements, downloads and an expanded explanation.
Why it works
When you make an exposure in your camera, all your calculations are based on doubling or halving the light, or fractions of it. These are normally expressed as f-stop changes, even if the shutter is being used to make the adjustment. The exposure to light is geometric not linear. An f-stop becomes a unit of exposure because it can be expressed in any of the variables relating to exposure (f-stop, shutter speed or ISO).
F-stop printing continues this process through to the exposure on your photographic paper to gain maximum control and repeatability in your printing, helping you make clear and accurate judgements.