Canon MARK IV User Manual (en)

Custom Function Settings
C.Fn IV -11     Start movie shooting
0: Default (from LV)
1: Quick start (<
I> button)
If the [6 Live View/Movie func. set.] menu option has been set to 
enable movie shooting (p.142), press the <I> button to start shooting 
a movie immediately while the camera is ready to shoot.
C.Fn IV -12     Focusing Screen
If you change the focusing screen, change this setting to match the 
focusing screen type. This is to obtain the correct exposure.
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.
About Super Precision Matte Ec-S and Maximum Lens Aperture
This focusing screen is optimized for f/1.8 to f/2.8 lenses.
If the lens maximum aperture is brighter than f/1.8, the center spot 
metering circle and Area AF frame might become difficult to see.
Also, if the lens maximum aperture is slower than f/2.8, the viewfinder 
will look darker.
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 come with 
the focusing screen.