Canon EF - Manual (Page 81)

BASIC OPERATION
0
Previewing Depth-of-Field
If you focus on a particular subject and take a
picture, some objects in front of and behind the main
subject will be "in focus" in the final photograph.
The distance between the nearest and farthest
objects, which appear sharp, is called "depth-of-
field." Three factors influence depth-of-field: the
f/stop at which the picture is taken, the focal length
of the lens, and the focused distance between the
camera and subject. Depth-of-field increases as the
lens is opened-up. At f/1.4, the maximum aperture
of the standard 50mm lens, depth-of-field is very
shallow permitting quick and easy focusing on the
main subject. At the same f/stop and focused
distance, lenses with short focal length (wide-angle
lenses) have inherently greater depth-of-field than
long lenses in the telephoto range. Also, at very close
distances between the camera and subject, any lens
has shallow depth-of-field. To preview depth-of-field
in the viewfinder of the EF, follow this procedure:
First operate the winding lever to cock the shutter.
After you have focused and composed your picture
in the normal way, check the aperture scale in the
viewfinder and note the f/stop selected by the
camera. Unlock the aperture ring and manually set it
at this f/stop. Push the multi-purpose lever in toward
46