Canon EOS 5D Instruction Manual page 124

Live View Shooting Cautions
Notes About the Shooting Results
When you shoot with the Live View function at high ISO speeds, noise
(horizontal banding, dots of light, etc.) or irregular colors may appear.
When you shoot continuously with the Live View function for a long
period, the camera's internal temperature may increase and it can
degrade image quality. Terminate Live View shooting when not shooting
images.
Before taking a long exposure, stop Live View shooting temporarily and
wait several minutes before shooting. This is to prevent image
degradation.
When you playback an image shot at high ISO speeds, noise or irregular
colors may appear.
If you take the picture during magnified view, the exposure might not
come out as desired. Return to the normal view before taking the picture.
During the magnified view, the shutter speed and aperture will be
displayed in red. Even if you take the picture during magnified view, the
image will be captured in the normal view.
Custom Function Notes
During Live View shooting, certain Custom Function settings will be
disabled (p.191-192).
If [8C.Fn II -4: Auto Lighting Optimizer] (p.196) is set to a setting
other than [3: Disable], the image may still look bright even if exposure
compensation or flash exposure compensation has been set to make the
exposure darker.
Notes About Lenses and Flash
The focus preset feature on super telephoto lenses cannot be used.
FE lock and modeling flash will not work if an external Speedlite is used.
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