Canon EOS 5D Mark III Instruction Manual page 368

Troubleshooting Guide
The Auto Lighting Optimizer cannot be set.
If [z3: Highlight tone priority] is set to [Enable], the Auto Lighting
Optimizer cannot be set. When [z3: Highlight tone priority] is set to
[Disable], then the Auto Lighting Optimizer can be set (p.148).
Even though I set a decreased exposure compensation, the
image comes out bright.
Set [z2: Auto Lighting Optimizer] to [Disable]. When [Standard/
Low/High] is set, even if you set a decreased exposure compensation or
flash exposure compensation, the image may come out bright (p.171).
The Live View image or movie shooting image is not
displayed during multiple-exposure shooting.
If [On:ContShtng] is set, Live View display, image review after image
capture, and image playback are not possible during shooting (p.179).
The multiple-exposure image is shot in 1 quality.
When the image-recording quality is set to 41 or 61, the
multiple-exposure image will be recorded in 1 quality (p.185).
When I use the <f> mode with flash, the shutter speed
becomes slow.
If you shoot at night when the background is dark, the shutter speed
becomes slow automatically (slow-sync shooting) so that both the subject
and background are properly exposed. To prevent a slow shutter speed,
under [z1: External Speedlite control], set [Flash sync. speed in
Av mode] to [1/200-1/60 sec. auto] or [1/200 sec. (fixed)] (p.194).
The flash does not fire.
Make sure the flash (or PC sync cord) is securely attached to the camera.
If you use a non-Canon flash unit with Live View shooting, set [z4:
Silent LV shoot.] to [Disable] (p.208).
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