Canon EOS Rebel T3 18-55mm IS II Kit Instruction Manual page 169

3 Setting the FlashN
Shutter sync.
Normally, set this to [1st curtain] so that the flash fires immediately
after the exposure starts.
If [2nd curtain] is set, the flash will fire right before the exposure
ends. When this is combined with a slow sync speed, you can create
a trail of light such as from car headlights at night. With 2nd-curtain
sync, a preflash is fired when you press the shutter button
completely. This is to determine the exposure. Then immediately
before the exposure ends, the real flash is fired. Therefore, two
flashes will be fired. However, with shutter speeds faster than 1/30
sec., 1st curtain sync will automatically take effect.
If an external Speedlite is attached, you can also set [Hi-speed]. For
details, see the Speedlite's instruction manual.
Flash exposure compensation
See "y Flash Exposure Compensation" on page 102.
E-TTL II flash metering
For normal flash exposures, set it to [Evaluative]. [Average] is for
advanced users. As with an external Speedlite, the metering area is
averaged. Flash exposure compensation may be necessary.
Clear flash settings
On the [External flash func. setting] screen, press the <B>
button to display the screen to clear the flash settings. When you
select [OK], the settings for the built-in flash and external
Speedlite will be cleared.
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