Canon EOS-1 D X Mark II Instruction Manual page 442

3 Custom Function Settings
Retract lens on power off
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 <2>.
ON : Enable
OFF : Disable
With auto power off, the lens will not retract regardless of the setting.
Before detaching the lens, make sure that it is retracted.
When [Enable] is set, this function takes effect regardless of the lens's
focus mode switch setting (AF or MF).
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