Canon EOS 250D Advanced User's Manual page 176

E-TTL II Flash Metering
Slow Synchro
[ ] 1/200-30sec. auto
z
The flash sync speed is set automatically within a range of 1/200 sec.
to 30 sec. to suit the scene's brightness. Slow-sync shooting is used
under some shooting conditions, in low-light locations, and shutter
speed is automatically lowered.
] 1/200-1/60sec. auto
[
z
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.
[ ] 1/200 sec. (fixed)
z
The flash sync speed is fixed at 1/200 sec. This more effectively
prevents subject blur and camera shake than with [1/200-1/60sec.
auto]. However, in low light, the subject's background will come out
darker than with [1/200-1/60sec. auto].
To use slow-sync shooting, set to [1/200-30sec. auto].
z
High-speed sync is not available in <f> or <d> mode when set to [1/200
z
sec. (fixed)].
For normal flash exposures, set it to
[Evaluative]. If [Average] is set, the flash
exposure will be averaged for the entire
metered scene. Depending on the scene,
flash exposure compensation may be
necessary. This setting is for advanced
users.
You can set the flash-sync speed for flash
photography in <f> or <d> mode.
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