Depth of field.
Because most subjects exist in more than one plane and have depth, it is
important in photography to have an area in which more than just a narrow
vertical plane will appear sharp. Depth of field depends on the focal length
of the lens, the lens stop, the distance from the point in focus to the lens,
b. Assume that a camera with a long focal length lens, and a camera with
a short focal length lens, are placed at equal distances from a subject.
this case, the depth of field is greater with the short focal length lens than
with the long focal length lens.