Canon EF - Manual (Page 51)

BASIC OPERATION
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Viewing and Focusing
The Canon EF is a single-lens-reflex (SLR) camera.
This means that you view the subject through the
same lens as is used to take the photograph.
Continuous viewing (except at the moment of
exposure) is made possible by the use of an
instant-return mirror located inside the body just
below the pentaprism. Since the picture you see in
the viewfinder is the same as the one recorded on the
film, parallax is completely eliminated. The view­
finder remains bright during AE operation, because
through-the-lens metering (TTL) is performed with
the lens at maximum aperture. Focusing is made
easier by a center spot microprism rangefinder. This
small round area in the center of the viewfinder
exaggerates the difference between the "in focus"
and "out of focus" image. By rotating the focusing
ring on the lens barrel until the center spot
microprism seems to disappear, the image is brought
into focus. For subjects with indistinct outlines, or
when using certain lenses (such as macro or
super-telephoto lenses), the entire ground glass area
of the viewfinder may be used for focusing. With the
exception of infrared film, when the image appears
sharp in the viewinder, it will be sharp on the film.
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