Canon EOS R5 C VR Creator Kit with RF 5.2mm f/2.8 Dual Fisheye Lens - Manual (Page 229)

How are multiple-exposure files numbered?
With the camera set to save all images, multiple-exposure image files are named with
the next number after the number of the last single exposure used to create them.
Will auto power off take effect during multiple-exposure shooting?
During multiple-exposure shooting, auto power off will not take effect. Note that before
you start multiple-exposure shooting, auto power off automatically takes effect at the
time set in the [
Auto power off ] option of [ : Power saving ], which will cancel multiple-
exposure shooting.
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