Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 508)

Troubleshooting Guide
508
Set [ z 3: Mirror lockup ] to [ Disable ].
Set the lens’s focus mode switch to < AF > (p.59).
Press the shutter button gently to prevent camera shake (p.61, 62).
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.231), set a higher ISO speed (p.163), use flash (p.260), or
use a tripod.
See “Minimizing Blurred Photos” on page 229.
Depending on the attached lens, the number of usable AF points and
patterns and Area AF frame’s shape vary. The lenses are categorized
into 11 groups from A to K (p.102). Check which group your lens
belongs to. Using a lens in groups G to K will have fewer usable AF
points (p.105-108).
I have to press the shutter button twice
completely to take a picture.
The image is out of focus or blurred.
There are fewer AF points or the shape of the
Area AF frame is different.