Canon MARK III EOS-1 DS Instruction Manual page 176

3 Custom Function Settings
C.Fn IV -10
0: Normal (enable)
1: Disable 6,5,Multi-controller
When the power switch is set to <1>, the <6>, <5>, and <9>
will be disabled from setting anything. The shutter button can still be
used to shoot. This prevents any settings to be changed inadvertently,
so it is convenient when you keep shooting with the same settings.
Even with setting 1, if the power switch is set to <J>, you can use <6>,
<5>, and <9> to change settings.
C.Fn IV -11
If you change the focusing screen, change this setting to match the
focusing screen type. This is to obtain the correct exposures.
0: lEc-C IV
Standard focusing screen (Laser-matte).
1: lEc-A, B, C, C II, C III, D, H, I, L
For Laser-matte screens.
2: pEc-S
For Super Precision Matte screens.
3: kEc-N,R
For New Laser-matte screens.
The pEc-S focusing screen is optimized for lenses whose maximum aperture
is f/1.8 to f/2.8. If the lens maximum aperture is brighter than f/1.8, the center
spot metering circle and Area AF ellipse might become difficult to see.
Also, if the lens maximum aperture is slower than f/2.8, the viewfinder will
look darker.
Even if all the Custom Functions are cleared, this setting will be retained.
Since the Ec-A, Ec-B, Ec-I, and Ec-L focusing screens have a prism at
the center, correct exposures cannot be obtained with evaluative
metering and center spot metering. Use either center-weighted average
metering or AF point-linked spot metering (except the center AF point).
To change the focusing screen, refer to the instructions that came with
the focusing screen.
176
Button function when 5 <OFF>
Focusing Screen