The New Photographer

DOF refers to distance within wherein the subjects are focused, i.e. how much of a photo is sharp in front and in back of where you focus on the main subject. If most of the photo is in focus, the DOF is high. If most of the photo (background) is blurry, with only the subject focused, the DOF is low. DOF is primarily controlled by aperture size, though DOF effects can be achieved by using photo editing software, or simply by placing a focused subject far away from its background.

F-stop numbers depict the size of the aperture.

Larger aperture sizes are represented by smaller f-stop numbers, and consequently a lower/shallower DOF.

For example:
SMALLER f-stop number (f2.8) = LARGER aperture = SHALLOWER DOF
BIGGER f-stop number (f22) = SMALLER aperture = GREATER DOF

Even more direct:
Small f-stop number (f2.8) = Shallower DOF
Bigger f-stop number (f22) = Greater DOF



(Only the subject is focused, with the rest blurry. Photo with low DOF)