Canon EOS REBEL T7 Basic Instruction Manual page 79

Shooting Conditions that Make Focusing Difficult
Low-contrast subjects such as the blue sky, solid-color flat surfaces
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or when highlight or shadow details are lost.
Subjects in low light.
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Stripes and other patterns where there is contrast only in the
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horizontal direction.
Subjects with repetitive patterns (Example: Skyscraper windows,
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computer keyboards, etc.).
Fine lines and subject outlines.
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Under a light source whose brightness, color, or pattern keeps
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changing.
Night scenes or points of light.
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The image flickers under fluorescent or LED lighting.
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Extremely small subjects.
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Subjects at the edge of the picture.
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Strongly backlit or reflective subjects (Example: Car with a highly
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reflective body, etc.).
The AF point covers both near and distant subjects (Example:
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Animal in a cage, etc.).
Subjects that keep moving within the AF point and cannot keep still
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due to camera shake or subject blur.
A subject approaching or moving away from the camera.
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Autofocusing while the subject is very far out of focus.
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Soft focus effect is applied with a soft focus lens.
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A special effect filter is used.
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Noise (dots of light, banding, etc.) appears on the screen during AF.
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Using AF to Focus (AF Method)
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