Canon EOS 250D Advanced User's Manual page 178

Flash mode
z
When using an external Speedlite, you can select the flash mode to suit
your desired photographic effects.
Shutter synchronization
z
Normally, set this to [First-curtain synchronization] so that the flash
fires immediately after the exposure starts.
If [Second-curtain synchronization] is set, the flash will be fired right
before the shutter closes. When this is combined with a slow shutter
speed, you can create a trail of light such as from car headlights at
night with a more natural feel. When second-curtain synchronization is
set together with [E-TTL II flash metering], the flash will be fired twice
in a row: once when you press the shutter button completely and once
right before the end of the exposure. Also, if the shutter speed is 1/100
sec. or faster, first-curtain synchronization will be applied automatically.
If an external Speedlite is attached, you can also select [High-speed
synchronization] (e). For details, refer to the Speedlite's instruction
manual.
Flash exposure compensation
z
For details, see "Flash Exposure Compensation" (= 171).
[E-TTL II flash metering] is the
z
standard mode of EL/EX-series
Speedlites for automatic flash
photography.
[Manual flash] is the mode for
z
advanced users who want to set
the [Flash output] (1/1 to 1/128)
themselves.
Regarding other flash modes, refer to
z
the instruction manual of a Speedlite
compatible with the respective flash
mode.
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