Canon EOS 5Ds Instruction Manual page 211

Exposure Compensation with Auto ISO
If the ISO speed is set to A (AUTO), you can set exposure
compensation (p.214) as follows:
• [z2: Expo.comp./AEB]
• Under [83: Custom Controls], use [s: Expo comp (hold btn,
turn )] (p.423).
• Quick Control (p.61)
If Auto ISO is set, the ISO speed setting will change to suit the shutter
speed and aperture in order to obtain a standard exposure. Therefore,
you may not obtain the desired exposure effect. In such a case, set the
exposure compensation.
If flash is used when Auto ISO is set, exposure compensation will not be
applied even if an exposure compensation amount is set.
Under [z2: Auto Lighting Optimizer], if the checkmark <X> for
[Disabled in M or B modes] is removed, Auto Lighting Optimizer can be
set even in the <a> mode (p.182).
When Auto ISO is set, you can press the <A> button to lock the ISO
speed.
If you press the <A> button and recompose the shot, you can see the
exposure level difference on the exposure level indicator compared to
when you pressed the <A> button.
If exposure compensation (p.214) was applied in <d>, <s>, or <f>
mode, and then the shooting mode is switched to <a> with Auto ISO
set, the exposure compensation amount already set will be maintained.
With Auto ISO set and [81: ISO speed setting increments] set to [1/2-
stop], any 1/2-stop exposure compensation will be implemented with the
ISO speed (1/3 stop) and shutter speed. However, the shutter speed
displayed will not change.
a: Manual Exposure
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