Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 107)

2.
Set the desired shutter speed.
Watch the top LCD panel as you turn the < > dial.
3.
Focus on the subject.
Press the shutter button halfway.
The aperture value is set automatically.
4.
Check the display and shoot.
As long as the aperture value is not blinking, the standard exposure will
be obtained.
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