Quote Originally Posted by BetterSense View Post
Certain multigrade filters claim an invariant exposure time between grades, or they provide a factor to calculate the new exposure time at the new contrast grades. Assume this works as it is supposed to.

So I make a test print. If my blacks are both too grey, and my whites are too grey, I suppose you can switch to the next-highest contrast grade and use the same exposure.

Now, suppose I make a print that needs more contrast. I find that the blacks are black enough, but the whites are grey. I switch to the next higher contrast grade. Should I change my exposure?

Suppose my current print has fine whites, but the blacks are too grey. I could increase my exposure to make the blacks blacker, but suppose I judge that that would wash out my highlights. I changed to the next highest contrast grade. Should I change my exposure in this case?

Equal exposure time for filters aims for the paper's ISO speed point, which is at 0.6 plus b+f density. This is lighter than Zone V, which has a density of 0.75, but the whole idea of not changing the exposure time when changing contrast only works with calibrated enlarger setups anyway. And even then, it's safe to assume that exposure needs to be slightly adjusted after a contrast change.

For most prints, I teststrip the exposure for the highlights and adjust the shadows with contrast. If you get significant highlights and shadows on one test strip, you can determine exposure and contrast in one go.