3Custom Function SettingsN 
Custom Functions are organized into four groups based on the function type: C.Fn I: Exposure, C.Fn II: Image, C.Fn III: Autofocus/Drive, C.Fn IV: Operation/Others.
C.Fn I: Exposure
C.Fn-1 Exposure level increments
0:1/3-stop
1:1/2-stop
Sets 1/2-stop increments for the shutter speed, aperture, exposure compensation, AEB, flash exposure compensation, etc. Effective when you prefer to control the exposure in less fine increments than 1/3-stop increments.
With setting 1, the exposure level will be displayed in the viewfinder and on the LCD monitor as shown below.
C.Fn-2 ISO expansion
0:Off
1:On
For the ISO speed, “H” (equivalent to ISO 12800) will be selectable. Note that if [C.Fn-6: Highlight tone priority] has been set to [1: Enable], “H” cannot be set.
C.Fn-3 Flash sync. speed in Av (Aperture-priority AE) mode
When you use flash in the aperture-priority AE mode (Av), you can set the flash sync speed.
0:Auto
The flash sync speed is set automatically within a range of 1/200 sec. to 30 sec. to suit the scene’s brightness. With an external Speedlite, high- speed sync is also possible.
1:1/200-1/60 sec. auto
Prevents a slow shutter speed from being set in low-light conditions. It is effective for preventing subject blur and camera shake. However, while the subject will be properly exposed with the flash, the background may come out dark.