Canon EOS 70D Instruction Manual page 421

The image is out of focus.
Set the lens focus mode switch to <AF> (p.40).
To prevent camera shake, press the shutter button gently (p.44, 45).
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.160), set a higher ISO speed (p.120), use flash (p.188, 193),
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 mode, or when servo takes effect in AI Focus AF mode
(p.75).
AF speed changes depending on lenses used.
If the AF method is set to [u+Tracking], [FlexiZone - Multi], or
[FlexiZone - Single] for Live View shooting or movie shooting, the AF
control method (phase-difference detection with the image sensor or
contrast detection) will switch automatically depending on the lens
used and functions selected, such as movie digital zoom or magnified
view. This can greatly affect the AF speed and the camera may take a
longer time to focus.
With FlexiZone - Multi, it takes longer to focus.
Depending on the shooting conditions, it may take longer to focus the
subject. Use FlexiZone - Single or focus manually.
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 117.
Troubleshooting Guide
421