The
depth of field is the region where the size of the circle of confusion is less than the resolution of the human eye (or of the display medium). Circles with a diameter less than the circle of confusion will appear to be in focus.
In photography, the circle of confusion (“CoC”) is used to determine the depth of field, the part of an image that is acceptably sharp. A standard value of CoC is often associated with each
image format, but the most appropriate value depends on visual acuity, viewing conditions, and the amount of enlargement. Properly, this is the
maximum permissible circle of confusion, but it is commonly referred to simply as the
circle of confusion