Canon EOS 70DN Basic Instruction Manual page 531

C.Fn I -6
0: Disable
1: Shutter speed/Aperture
This takes effect in the shutter-priority AE (s) and aperture-priority AE
(f) modes. If the subject brightness changes and the standard exposure
cannot be obtained within the autoexposure range, the camera will
automatically change the manually-selected setting to obtain a standard
exposure.
2: ISO speed
This works in the Program AE (d), shutter-priority AE (s), and aperture-
priority AE (f) modes. If the subject brightness changes and the standard
exposure cannot be obtained within the autoexposure range, the camera
will automatically change the manually set ISO speed to obtain a standard
exposure.
Under [z3: ISO speed settings], even if [ISO speed range] or [Min.
shutter spd.] is changed from the default setting, safety shift will
override it if a standard exposure cannot be obtained.
The minimum and maximum ISO speeds of the safety shift using the ISO
speed will be determined by the [Auto ISO range] setting (p.124).
However, if he manually set ISO speed exceeds the [Auto ISO range],
the safety shift will take effect up to the manually set ISO speed.
If [Shutter speed/Aperture] or [ISO speed] is set, safety shift will take
effect if necessary even when flash is used.
Safety shift
3 Custom Function SettingsN
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