Canon EOS 750D Instruction Manual page 345

C.Fn-13
This is to set the lens retraction mechanism for when a gear-driven
STM lens (such as EF40mm f/2.8 STM) is attached to the camera.
You can set it to retract the extended lens automatically when the
camera's power switch is set to <OFF>.
0: Enable
1: Disable
With auto power off, the lens will not retract regardless of the setting.
Before detaching the lens, make sure that it is retracted.
With setting 0, this function takes effect regardless of the lens's focus mode
switch setting (AF or MF).
Retract lens on power off
3 Custom Function SettingsK
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