Canon EOS 6D Instruction Manual page 359

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.43,

44).
If the lens has an Image Stabilizer, set the IS switch to <1>

(p.42).
In low light, the shutter speed may become slow. Use a faster

shutter speed (p.144), set a higher ISO speed (p.106), use flash
(p.170), 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.69).
The continuous shooting speed is slow.
Depending on the shutter speed, aperture, subject conditions,

brightness, etc., the continuous shooting speed may become
slower.
The maximum burst during continuous shooting is lower.
If you shoot something that has fine detail (such as a field of

grass), the file size will be larger and the actual maximum burst
may be lower than the number mentioned on page 103.
Troubleshooting Guide
359