Canon EOS-1D Mark IV - Manual (Page 218)

Custom Function Settings
C.Fn III: Autofocus/Drive
C.Fn JH -1 USM Jens electronic MF
The USM lens electronic MF can be enabled or disabled when you use any
of the following lenses.
EF 50mm f/1 .OL USM, EF 85mm f/1.21 USM,
EF 85mm f/1,2L II USM, EF 200mm f/1,8L USM,
EF 300mm f/2.8L USM, EF 400mm f/2.8L USM,
EF 400mm f/2.8L II USM, EF 500mm f/4.5L USM,
EF 600mm f/4L USM, EF 1200mm f/5.6L USM,
EF 28-80mm f/2.8-4L USM
0: Enable after One-Shot AF
After focus is achieved in One-Shot AF, electronic MF is enabled. If C.Fn
IV -1-2/3 is set, it is also enabled before focus is achieved.
1: Disable after One-Shot AF
After focus is achieved in One-Shot AF, electronic MF is disabled. If
C.Fn IV -1-2/3 is set, it is possible before focus is achieved.
2: Disable in AF mode
Electronic MF is disabled in the AF mode.
C.Fn III -2 Al Servo tracking sensitivity
During focusing in Al Servo AF mode, the AF sensitivity for tracking subjects (or
obstacles) moving into the AF points can be set to one of five levels.
If it is set toward [Slow], interruptions by any obstacles will be less
disruptive. It makes it easier to keep tracking the target subject.
If it is set toward [Fast], it will be easier to focus any subject which suddenly
enters the picture from the side. Convenient when you want to successively
photograph multiple subjects located at random distances.
C.Fn III -3 Al Servo 1st/2nd image priority
When Al Servo AF is used with continuous shooting, you can change the
Servo’s operation characteristics and shutter-release timing.
0: AF priorlty/Tracking priority
For the first shot, focusing the subject is given priority. For the second and following
shots during continuous shooting, focus-tracking of the subject is given priority.
1; AF priority/Drive speed priority
For the first shot, focusing the subject is given priority. During continuous shooting,
the continuous shooting speed is given priority over the focus-tracking of the subject.
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