Olympus IS-1 - Manual (Page 56)

Autofocus (AF)
The Autofocus (AF) mechanism automatically
adjusts focus by measuring the distance-to-subject.
Focusing is accomplished by a TTL (through-the-
lens) phase-difference detection system. More
simply, an AF sensor catches the light reflected
off of the subject, calculates the distance, and
activates the lens to focus. The IS-1 AF system
is particularly advanced, because it even works in
the dark by using an infrared beam of light.
Autofocus is designed to focus on whatever
appears in the center of the viewfinder. If you
wish to position your subject outside the
center of the frame you can use the focus lock
(see p. 21). This will also lock the proper
exposure (AE lock).
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