We know by now that a camera lens does not focus at multiple distances at the same time. There is only one place that will be in perfect focus from the focal plane, and that is determined by where you focus the lens. When we focus a lens, there is only one focal plane to subject distance that is in perfect focus.

Yet we see that some areas in front of, and some areas behind our point of focus can also look sharp and that range can be different depending on some specific criteria. This zone that we perceive as being sharp versus the area that we perceive as being soft is what we are calling the “depth of focus”.