Canon EOS Rebel T4i 18-135mm IS STM Lens Kit Instruction Manual page 322

Troubleshooting Guide
The card cannot be used.
If a card error message is displayed, see page 32 or 331.
The image is out of focus.
Set the lens focus mode switch to <AF> (p.39).
To prevent camera shake, press the shutter button gently (p.42, 43).
If the lens has an Image Stabilizer, set the IS switch to <1>.
In low light, the shutter speed may become slow. Use a faster shutter
speed (p.108), set a higher ISO speed (p.90), use flash (p.104), or use
a tripod.
I cannot lock the focus and recompose the shot.
Set the AF operation to One-Shot AF. Focus lock is not possible in the
AI Servo AF and AI Focus AF operations (p.95).
The continuous shooting speed is slow.
Depending on the lens type, shutter speed, aperture, subject
conditions, brightness, etc., the continuous shooting speed may
become slower.
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