H ere is a simple way to adjust exposure in the f-stop increments that is second nature to photographers. The key to this technique is that the Screen and Multiply layer blending modes, at an opacity of 38%, produce an effect very similar to lightening or darkening by one full f-stop. (For half-stop adjustments, use 19% opacity, for one-third stop use 13%, and so on.) In this example, we’ll darken the image by one stop.