The two areas where focus may be adjusted in the camera are:

• Depth of focus
• Depth of field

Depth of focus - This is the distance through which the film may be moved before the image of a flat object becomes noticeably unsharp.

This can most easily be seen with a 5 x 4 camera. This is likely only to be significant if a sheet of film is bowed and not flat, for example in a large format camera, 10" x 8" or larger.

Depth of focus cannot be seen with a 35mm camera as the film plane is fixed. The film is kept in an exact position by a plate attached to the back of the camera. The exact position of the film plane if needed for measurement is shown by a circle with a line though it.

Depth of focus limits set a tolerance on the necessary flatness and perpendicularity of the film plane. Such tolerances become increasingly smaller with small format cameras using lenses of large maximum aperture and short focal length.