If Zone zero shows no difference in density from the step(s) just above it, then the film has received insufficient exposure. In this case, it is easy to judge how much additional exposure is needed: count the steps until you can see good density changes on the negative....Where you begin to see density changes, that step is Zone zero. Since each step represents a half-stop change in exposure, it’s possible to calculate how to change the exposure index. For example, if I set my light meter to ISO 400, and significant density changes are seen only down through the 3rd from last step (step 19), then that’s actually receiving the Zone zero exposure, and the film speed on the light meter needs to be set at 200 to give one stop more exposure to the film. I then repeat the test to double check my assumptions. The film speed I’ve chosen at this point will be the one I’ll use for this film.
Bookmarks