Depth-Of-Field Preview - Canon EOS 1D Mark III Instruction Manual

Aperture Display
The larger the f/number, the smaller the aperture opening will be. The
aperture values displayed will differ depending on the lens. If no lens is
attached to the camera, "00" will be displayed for the aperture value.

Depth-of-Field Preview

A higher f/number will make more of the foreground and background fall
within acceptable focus. However, the viewfinder will look darker.
If the depth of field is difficult to discern, hold down the depth-of-field
preview button while turning the <6> dial.
The exposure will be locked (AE lock) while the depth-of-field preview
button is pressed.
If the "30"" shutter speed blinks, it indicates
underexposure.
Turn the <6> dial to set a larger aperture
(smaller f/number) until the blinking stops or
set a higher ISO speed.
If the "8000" shutter speed blinks, it
indicates overexposure.
Turn the <6> dial to set a smaller
aperture (larger f/number) until the blinking
stops or set a lower ISO speed.
Press the depth-of-field preview button
to stop down to the current aperture
setting. You can check the depth of field
(range of acceptable focus) through the
viewfinder.
f: Aperture-Priority AE
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