Canon EOS 1D Software Instruction Manual page 188

Personal Function Settings
Sets the maximum and minimum apertures to be used
Select the maximum and minimum apertures from the list box.
For example, if you set 1.4 for the largest aperture and 8.0 for the smallest aperture, the
usable aperture range will be f/1.4 to f/8.0.
You can better control the apertures used by setting the range of usable apertures.
Specify a minimum aperture value that is smaller than the maximum aperture setting.
If you select a minimum aperture value that is larger than the maximum aperture, a
warning message appears and the setting reverts to the default value.
If you set the maximum and/or minimum aperture to one that is not a full-stop
increment (such as f/4.5), the controllable and settable aperture range might not be
as exact as you set it. (A slight deviation may occur.) This applies if you also set
Custom Function C.Fn-6-1 or C.Fn-6-2 and set the maximum and/or minimum
aperture to one that is not a full-stop increment (such as f/6.3).
If the largest aperture of the attached lens is smaller than the largest aperture you set
with P.Fn-05, the largest aperture will be set to the largest aperture of the lens. And if
the smallest aperture of the attached lens is larger than the smallest aperture you set
with P.Fn-05, the smallest aperture will be set to the smallest aperture of the lens.
If safety shift has been enabled (with C.Fn-16), it will override P.Fn-05's aperture
range.
Registers and switches the shooting mode and metering mode
While you press the <
setting (such as the aperture for aperture-priority AE), metering mode, and exposure
compensation amount.
Select settings that are appropriate for each shooting mode.
The modes and settings are preset with the camera.
See "Registering the Modes and Settings with the Camera" for information on the camera
procedures (M-65).
Convenient when you want to instantly select the preset modes and settings to suit a
particular shooting situation such as backlit or front-lit conditions.
M-64
> button, you can select the preset shooting mode, exposure