Canon EOS40D instruction manual When Autofocus Fails, Subjects difficult to focus

When Autofocus Fails

Autofocus can fail to achieve focus (the focus confirmation light <o> blinks) with certain subjects such as the following:

Subjects difficult to focus

Low-contrast subjects

Example: Blue sky, solid-color walls, etc. Subjects in low light

Extremely backlit and reflective subjects Example: Car with a reflective body, etc. Overlapping near and far objects Example: Animal in a cage, etc. Repetitive patterns

Example: Skyscraper windows, computer keyboards, etc.

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. (p.48)

(2)Set the lens focus mode switch to <MF> and focus manually.

Manual Focusing

1 Set the lens focus mode switch to <MF>.

2 Focus the subject.

Focus by turning the lens focusing ring until the subject looks sharp in the viewfinder.

If you press the shutter button halfway during manual focusing, the active AF point and the focus confirmation light <o> in the viewfinder will light when focus is achieved.

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