3Custom Function SettingsN
C.Fn-14 E-TTL II
0:Evaluative
Fully automatic flash photography for all conditions, from low light to daylight fill-flash.
1:Average
The flash is averaged for the entire area covered by the flash. Since automatic flash exposure compensation will not be executed, you may have to set it yourself depending on the scene. This also applies if you use FE lock.
C.Fn-15 Shutter curtain sync.
0:1st-curtain sync.
1:2nd-curtain sync.
When a slow shutter speed is set, you can capture a light trail following the 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 the EX-series Speedlite has this feature, it will override this Custom Function.
When 2nd-curtain sync is used, a preflash will be fired for flash metering control right after you press the shutter button completely. Remember that the main flash will fire right before the shutter closes.
C.Fn-16 Safety shift in AV or TV
0:Disable
1:Enable
This works in the shutter-priority AE (Tv) and aperture-priority AE (Av) modes. If the subject’s brightness changes suddenly and the current shutter speed or aperture becomes unsuitable, the shutter speed or aperture is shifted automatically to obtain a suitable exposure.