Canon EOS REBEL T7i Instruction Manual page 192

a: Manual Exposure
Exposure Compensation with ISO Auto
If the ISO speed is set to [AUTO] for manual exposure shooting, you
can set exposure compensation (p.196) as follows:
 [z2: Expo.comp./AEB]
 [5:Expo comp (hold btn, turn S)] with [13: Assign SET button]
under [54: Custom Functions(C.Fn)] (p.397)
 Quick Control (p.59)
If ISO Auto is set, the ISO speed setting will change to obtain the

standard exposure with the set shutter speed and aperture. Therefore,
you may not obtain the desired exposure effect. In such a case, set the
exposure compensation.
If flash is used when ISO Auto 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

[Disable during man expo] is removed, Auto Lighting Optimizer can be
set even in the <a> mode (p.169).
When ISO Auto 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 the <A> button was pressed.
If exposure compensation (p.196) was applied in <d>, <s>, or <f>

mode, the exposure compensation amount already set will still be
maintained when the shooting mode is switched to <a> with ISO Auto
set.
D Using the Built-in Flash
To obtain a correct flash exposure on the main subject, the flash output
will be set automatically (autoflash) to match the manually-set aperture.
Note that the range of settable shutter speed will be limited within 1/200
sec. to 30 sec or to bulb.
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