Film speed tests are necessary whenever I change films to one I have not used before.
So, when I bought some boxes of Ilford FP4 sheet film to try out, I needed to test for film speed and normal development time.
Finding Correct Film Speed
You set your camera’s meter or hand-held light meter with a film speed setting, usually referred to as an ISO or ASA setting. Ilford FP4 has a box speed of 125 ISO, set by the manufacturers. Finding a correct film speed for your style of photography is essential.
With my landscape photography, I usually need to exercise fine exposure control to preserve shadow detail in the final prints. It has been my experience to halve the manufacturer’s box speed.
Film Development and Contrast Control
Another side of the same problem to maximising shadow detail, is maintaining good textural control in the print’s high values. Unlike the shadows which are affected more by exposure based on ISO, highlights are affected by time in development.
Therefore, finding the correct development time to suit the contrast of your subject matter is crucial.
Use Just 2 Sheets of 4×5 Film
The test I describe here is best suited to sheet film users who print with diffused enlarger light sources. I use step wedges and contact printing in the darkroom. It can be completed with just 2 sheets of 4×5 film.
I wrote this popular article several years ago and have recently re-edited parts of it. It is now available as a convenient downloadable pdf file that you can keep on file or mobile, so it can be referred to easily.
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