Difficult Subjects For Autofocus - Canon EOS 1 Instructions Manual

3. Difficult Subjects for Autofocus

This camera's autofocus system is very accurate and can quickly focus
most subjects with the high-precision Multi-BASIS (Base-Stored Image
Sensor) AF sensor equipped with five focusing points as shown below.
However, the system may have difficulty focusing the subjects listed
below. When autofocus is impossible, the green in-focus indicator will
blink in the viewfinder.
• Position of invidual sensor of BASIS
(a)
(b)
34
Cross-sensor
(a) Low contrast subjects (misty scenes,
light-colored or white objects)
(b) Subjects in extremely low-light situa-
tions (a dark room, night scenes)
(c) Subjects in extremely strong backlight,
or with bright spectral reflections (shiny
metal, snow, ice, surface of a lake)
(d) Subjects with an object in front of them
(caged zoo animals)
(e) Subjects having generally horizontal
patterns (only when using the center
focusing point, when using lenses with
maximum aperture smaller than f/2.8)
(f) Subjects having generally vertical pat-
terns (only when using focusing points
other than the center)
Focus these subjects as follows:
1) Particularly with subjects such as (a),
focus on a substitute subject at the same
distance from the camera as your main
subject, then recompose the picture
using the focus lock function.
2) In the case of (e), there is no problem
when using a lens with a maximum aper-
ture of f/2.8 or larger (except the
EF50mm f/2.5 Compact Macro or EF28-
80mm f/2.8-4L) because the camera's
central cross-sensor activates to detect
horizontal lines. However, when using a
lens with a maximum aperture smaller
than f/2.8, we recommend to use the
focusing points other than the center that