Canon MARK IV User Manual (en)

Troubleshooting Guide
Set [8C.Fn II -4: Auto Lighting Optimizer] to [3: Disable]. If it is set 
to [Standard/Low/Strong], the image might still come out bright even 
if you set a darker exposure with manual exposure, exposure 
compensation, or flash exposure compensation (p.81, 215).
Set [8C.Fn II -2: High ISO speed noise reduction] to one of the 
following settings: [Standard/Low/Disable]. If it is set to [Strong], the 
maximum burst will greatly decrease (p.214).
If you shoot a subject which has fine detail (field of grass, etc.), the file 
size will be larger and the actual maximum burst might be lower than 
the number mentioned on page 61.
If [8C.Fn II -3: Highlight tone priority] is set to [Enable], the 
settable ISO speed range starts from ISO 200. If [Disable] is set, ISO 
100 can be set (p.215).
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. If you do not want a 
slow shutter speed to be set, set [8C.Fn I -15: Flash sync. speed in 
Av mode
] to 1 or 2 (p.212).
Make sure the flash (or PC sync cord) is securely attached to the 
A darker exposure was set with exposure 
compensation, but the image looks bright.
The maximum burst during continuous shooting is lower.
ISO 100 cannot be set.
When I use the <f> mode with flash, the shutter speed becomes slow.
The flash does not fire.