Canon EOS 5D Mark III Instruction Manual (en)

Turn the dioptric adjustment 
Turn the knob left or right so that the 
AF points in the viewfinder look 
If the knob is difficult to turn, remove 
the eyecup (p.187).
To obtain sharp images, hold the camera still to minimize camera 
1. Wrap your right hand around the camera grip firmly.
2. Hold the lens bottom with your left hand.
3. Rest your hand’s right index finger lightly on the shutter button.
4. Press your arms and elbows lightly against the front of your body.
5. To maintain a stable stance, place one foot slightly ahead of the other.
6. Press the camera against your face and look through the viewfinder.
Basic Operation
Adjusting the Viewfinder Clarity
Holding the Camera
If the camera’s dioptric adjustment still cannot provide a sharp viewfinder 
image, using Dioptric Adjustment Lens Eg (sold separately) is recommended.
Vertical shooting
Horizontal shooting
To shoot while looking at the LCD monitor, see page 68.