Subjects Difficult To Focus; Mf: Manual Focusing - Canon REBEL T3I EOS 600D User Manual

Subjects Difficult to Focus

Autofocus can fail to achieve focus (viewfinder's focus confirmation light
<o> blinks) with certain subjects such as the following:
Very low-contrast subjects.
(Example: Blue sky, solid-color walls, etc.)
Subjects in very low light
Extremely backlit or reflective subjects
(Example: Car with a highly reflective body, etc.)
Near and far subjects covered by an AF point
(Example: Animal in a cage, etc.)
Repetitive patterns
(Example: Skyscraper windows, computer keyboards, etc.)
In such cases, do one of the following:
(1) With One-Shot AF, focus an object at the same distance as the
subject and lock the focus before recomposing (p.53).
(2) Set the lens focus mode switch to <MF> and focus manually.
For conditions where AF can fail to achieve focus with [Live mode]/[u Live
mode] during Live View shooting, see page 134.

MF: Manual Focusing

Focusing ring
If you hold down the shutter button halfway during manual focusing, the AF
point achieving focus will light in red briefly, the beeper will sound, and the
focus confirmation light <o> in the viewfinder will light.
Set the lens focus mode switch to
1
<MF>.
Focus the subject.
2
Focus by turning the lens focusing
ring until the subject looks sharp in
the viewfinder.
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