Canon EOS 1D Mark II N Instruction Manual page 167

C.Fn-15
0: 1st-curtain synchronization
1: 2nd-curtain synchronization
By using a slow sync speed, you can create a light trail following a moving
subject. The flash fires right before the shutter closes. This Custom Function
can be used to obtain 2nd-curtain sync effects even with EX-series
Speedlites which do not have this feature. If an EX-series Speedlite having
this feature is set for 2nd-curtain sync, it will override this Custom Function.
C.Fn-16
Safety shift can be set for the shutter-priority AE and aperture-priority AE modes.
0: Disable
1: Enable
If the subject's brightness changes suddenly and the current shutter-priority
AE or aperture-priority AE setting becomes unsuitable, the shutter speed or
aperture is shifted to obtain a suitable exposure automatically.
C.Fn-17
0: Single AF point
1: Expand (TTL. of 7 AF points)
The AF point activation area expands by one point all around the manually-
selected AF point. A total of 7 AF points become active. This setting is
effective for when only one manually-selected AF point is unable to focus
track a subject moving erratically.
2: Automatic expand (max. 13)
The camera automatically sets the AF point activation area to 7 or 13 points
to suit the lens focal length and AF mode.This is effective when the subjectís
movement is unpredictable.
The AF point activation area centers on the selected AF point. Therefore, if a peripheral
AF point is selected, the AF point activation area will be smaller as shown below.
7-point activation area
Selected AF point
Setting C.Fn-13 will also expand the AF point activation area.
Shutter curtain synchronization
Safety shift in Av or Tv
AF point activation area
Activation area
3 Custom Function Settings
13-point activation area
167