Canon EOS REBEL T6i 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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