Canon EOS-1 DX Mark III Advanced User's Manual page 339

Shooting Conditions That Make Focusing Difficult
Subjects with very low contrast.
(Example: Blue skies, solid-color flat surfaces, etc.)
Subjects in very low light.
Strongly backlit or reflective subjects.
(Example: Cars with highly reflective surfaces, etc.)
Near and distant subjects positioned close to an AF point.
(Example: Animals in cages, etc.)
Light source such as dots of light positioned close to an AF point.
(Example: Night scenes, etc.)
Subjects with repetitive patterns.
(Example: Skyscraper windows, computer keyboards, etc.)
Subjects with finer patterns than an AF point.
(Example: Faces or flowers as small as or smaller than an AF point, etc.)
In such cases, focus in either of the following two ways.
1. With One-Shot AF, focus on an object at the same distance as the subject and lock the
focus, then recompose the shot (
2. Set the lens's focus mode switch to <
Note
Depending on the subject, focus may be achieved by slightly recomposing the shot
and performing AF operation again.
).
> and focus manually (
339
).