Canon EOS REBEL T7i Instruction Manual page 442

Troubleshooting Guide
I cannot lock the focus and recompose the shot.
Set the AF operation to One-Shot AF. Focus lock is not possible in the
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AI Servo AF mode or when servo takes effect in AI Focus AF mode
(p.118).
Horizontal stripes appear, or the exposure or color tone
look strange.
Horizontal stripes (noise) or irregular exposures can be caused by
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fluorescent lighting, LED lighting, or other light sources during
viewfinder or Live View shooting. Also, the exposure or color tone may
not come out right. A slow shutter speed may reduce the problem.
The standard exposure cannot be
obtained or the exposure is irregular.
During viewfinder shooting or Live View shooting, if you use a TS-E
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lens (except the TS-E17mm f/4L or TS-E24mm f/3.5L II) and shift or tilt
the lens or use an Extension Tube, the standard exposure may not be
obtained or the exposure may be irregular.
The continuous shooting speed is slow.
The maximum continuous shooting speed may become slower

depending on the shutter speed, aperture, subject conditions,
brightness, lens, flash use, temperature, battery type, remaining
battery level, shooting function settings, etc. For details, see page 142.
The maximum burst during continuous shooting is lower.
If you shoot something that has fine detail such as a field of grass, the
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file size will be larger, and the actual maximum burst may be lower
than the number listed on page 147.
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