Canon EOS 750D Instruction Manual page 124

g: Changing the ISO Speed to Suit the LightK
ISO [AUTO]
Shooting Mode
A/7/C/2/4/5
3
C/P/x/6/G
8
F
d/s/f/a
With bulb exposures
*1: Depends on the maximum ISO speed limit set (p.123).
*2: (1) If fill flash results in overexposure, ISO 100 or a higher ISO speed will be
set.
(2) In the C, 2, 3, 4, 5, x, P, and <d> modes, if you use bounce
flash with an external Speedlite, the ISO speed will be automatically set
within ISO 400 - ISO 1600 (or up to the maximum limit).
When [AUTO] is set, the ISO speed is indicated in whole-stop increments.
However, the ISO speed is actually set in finer increments. Therefore, in the
image's shooting information (p.306), you may find an ISO speed such as
ISO 125 or ISO 640 displayed as the ISO speed.
124
If the ISO speed is set to [AUTO], the
actual ISO speed setting will be
displayed when you press the shutter
button halfway. As indicated below, the
ISO speed will be set automatically to
suit the shooting mode.
ISO Speed Setting
No Flash
ISO 100 - ISO 6400
ISO 100 - ISO 1600
ISO 100 - ISO 6400
ISO 100 - ISO 12800
ISO 100 - ISO 6400
ISO 400
With Flash
*2
ISO 400
(Except in the A, C,
6, and F modes.)
*1