Canon EOS 5Ds Instruction Manual page 283

ISO Speed in the <A> Mode
The ISO speed will be set automatically within ISO 100 - ISO 6400.
ISO Speed in the <d>, <s>, <f>, and <F> Modes
The ISO speed will be set automatically within ISO 100 - ISO 6400.
Under [z2: ISO speed settings], if you set the [ISO speed
range]'s [Maximum] setting to [H (12800)] in the <d>, <f>, or
<F> mode (p.161), the automatic ISO range will be expanded to H
(equivalent to ISO 12800). Even if you set the [Maximum] and
[Minimum] to a narrower range than the default ISO range (ISO 100
- ISO 6400), it will not take effect.
If [z3: Highlight tone priority] is set to [Enable] (p.187), the
automatic ISO range will be ISO 200 - ISO 6400.
Under [z2: ISO speed settings], [Auto ISO range] and [Min.
shutter spd.] cannot be set (p.162-163) for movie shooting. [z2:
ISO speed settings] cannot be selected in the <s> mode.
If [Minimum] is set to [L(50)] in [ISO speed range], and you switch from still
photo shooting to movie shooting, the minimum setting for automatic ISO
range for movie shooting will be ISO 100. It cannot be expanded to ISO 50.
k Shooting Movies
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