Canon EOS 3 User Manual (en)

7. When Autofocus Fails
Autofocus can fail to achieve focus (the in-focus indicator blinks) with
certain subjects such as the following:
(a) Low-contrast subjects.
(b) Subjects in low light.
(c) Extremely backlit or reflective subjects.
(d) Overlapping near and far objects.
In such cases, do one of the following:
(1) Focus an object at the same distance as the subject and lock the
focus before recomposing.
(2) Set the lens focus mode switch to MF (or  on older lenses) and
focus manually.
• You can also use the focusing aid. Select any focusing point and focus manually
while pressing the shutter button halfway. When focus is achieved, the selected
focusing point will light together with the in-focus indicator.
• When the focusing point is automatically selected or eye-selected, the center
focusing point flashes and the in-focus indicator lights when focus is achieved.
• Full-time manual focus enables you to switch to manual focus anytime after the
lens starts to autofocus. This feature is available in the One-Shot AF mode with
USM (Ultrasonic Motor) lenses having a distance scale.
For USM lenses with an electronic focusing ring (such as the EF 200mm f/1.8L),
Custom Function CF-7 may require the lens focus mode switch to be set to MF (or
M) before manual focus is enabled. See page 112.
If focusing cannot be achieved even while the Speedlite or ST-E2's AF-assist lamp is
on, select the center focusing point to autofocus. The other focusing points might not
achieve focus as readily as the center focusing point.
 04. C836-E (33~)  28-01-2003  11:11  Pagina 51