Canon EOS Rebel XT - Manual (Page 150)

3 Custom Function SettingsN
150
C.Fn-7 Mirror lockup
0: Disable
1: Enable
Effective for close-up and telephotos shots to prevent camera
shake caused by the mirror’s reflex action. For more on mirror
lockup, see page 94.
C.Fn-8 E-TTL II
0: Evaluative
Fully automatic flash photography under all conditions, from low
light to daylight fill-flash.
1: Average
The flash exposure is averaged for the entire area covered by the
flash. Since the camera will not execute automatic exposure
compensation, adjust the flash exposure compensation if
necessary. This also applies if you use FE lock.
C.Fn-9 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 provide 2nd-
curtain sync. 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.