Canon EOS 7D Mark II Instruction Manual page 498

Troubleshooting Guide
I have to press the shutter button twice completely
to take a picture.
If [z4: Mirror lockup] is set to [Enable], set it to [Disable].
The image is out of focus.
Set the lens's focus mode switch to <AF> (p.50).
Press the shutter button gently to prevent camera shake (p.54-55).
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.218), set a higher ISO speed (p.154), use flash (p.254, 259),
or use a tripod.
There are fewer AF points.
Depending on the attached lens, the number of usable AF points and
patterns will differ. The lenses are categorized into seven groups from
A to G. Check which group your lens belongs to. Using a lens in
Groups E to G will have fewer usable AF points (p.102-103).
The AF point is blinking or two AF points are displayed.
The AF point at the registered area is blinking (p.94, 450).
The manually-selected AF point (or zone) and the registered AF point
are displayed (p.93, 450).
The AF points do not light up in red.
The AF points light up in red when focus is achieved in low-light
conditions.
In the <d>, <s>, <f>, <a>, and <F> modes, you can set
whether to have the AF points light in red when focus is achieved
(p.131).
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