Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 837)

Same expo. for new aperture
The maximum aperture value may decrease (the lowest f/number may increase) in < >
mode (manual exposure shooting) with ISO speed set manually (except when set to ISO
Auto) if you (1) Change lenses, (2) Attach an extender, or (3) Use a zoom lens with a
variable maximum aperture value. This function prevents the corresponding underexposure
by adjusting ISO speed or shutter speed (Tv) automatically to maintain the same exposure
as before (1), (2), or (3).
With [
ISO speed/Shutter speed ], the ISO speed is automatically adjusted within the ISO
speed range. If exposure cannot be maintained by adjusting ISO speed, shutter speed (Tv
value) is automatically adjusted.
OFF: Disable
ISO: ISO speed
ISO/Tv: ISO speed/Shutter speed
Tv: Shutter speed
Caution
Does not respond to changes in effective aperture value from changes in
magnification when macro lenses are used.
Cannot provide the same exposure as before (1), (2), or (3) if [
ISO speed ] is set
and the exposure cannot be maintained at speeds set in [ ISO speed range ].
Cannot provide the same exposure as before (1), (2), or (3) if [ Shutter speed ] is
set and the exposure cannot be maintained at speeds set in [ 3 : Set shutter
speed range ].
Note
Also responds to changes in the highest f/number (minimum aperture).
The original exposure setting is restored if you perform (1), (2), or (3) with [
ISO
speed ], [ ISO speed/Shutter speed ], or [ Shutter speed ] set and do not adjust ISO
speed, shutter speed, or aperture value before returning the camera to the original
state, before (1), (2), or (3).
Shutter speed may change to maintain exposure if the ISO speed increases to an
expanded ISO speed when [
ISO speed ] is set.
837