Canon EF - Manual (Page 53)

• In fast-breaking situations, or in candid shooting,
you can prefocus the lens by using the distance scale
engraved on top of the lens barrel. Estimate the
distance between you and the subject. Then turn the
focusing ring until this distance (in feet or meters) is
aligned with the focusing index mark. This method is
especially useful when there is not enough time for
through-the-lens focusing, or when you do not want
to draw attention to yourself by lifting the camera
to eye level.
• Film Plane Indicator—the-e-mark engraved on the
camera just to the left of the pentaprism indicates
the exact position of the film plane. This is an aid
when actually measuring the film-to-subject distance
in macrophotography.
• Black and White Infrared Photography: Because
infrared light rays focus on a plane slightly behind
that of ordinary light rays, it is necessary to modify
slightly the normal method of focusing the lens.
First, focus on the main subject as usual. Next, take
note of the focused distance (in feet or meters)
which appears opposite the focusing index mark.
Then, turn the focusing ring slightly, so that the
focused distance is aligned with the tiny red dot
engraved on the lens barrel just to the right of the