Canon EOS M Instruction Manual page 221

[Flash sync. speed in Av mode]
: Auto
The flash sync speed is set automatically within a range of 1/200 The flash sync speed is set automatically within a range of 1/200 The flash sync speed is set automatically within a range of 1/200
sec. to 30 sec. to suit the scene's brightness. High-speed sync is sec. to 30 sec. to suit the scene's brightness. High-speed sync is sec. to 30 sec. to suit the scene's brightness. High-speed sync is
also possible.
: 1/200-1/60 sec. auto
Prevents a slow shutter speed from being set in low-light conditions. Prevents a slow shutter speed from being set in low-light conditions. Prevents a slow shutter speed from being set in low-light conditions.
It is effective for preventing subject blur and camera shake. It is effective for preventing subject blur and camera shake. It is effective for preventing subject blur and camera shake.
However, while the subject will be properly exposed with the flash, However, while the subject will be properly exposed with the flash, However, while the subject will be properly exposed with the flash,
the background may come out dark. the background may come out dark. the background may come out dark.
: 1/200 sec. (fixed) : 1/200 sec. (fixed) : 1/200 sec. (fixed)
The flash-sync speed is fixed at 1/200 sec. This more effectively The flash-sync speed is fixed at 1/200 sec. This more effectively The flash-sync speed is fixed at 1/200 sec. This more effectively
prevents subject blur and camera shake than with [1/200-1/60 sec. prevents subject blur and camera shake than with [ prevents subject blur and camera shake than with [
auto]. However, in low light, the subject's background will come out ]. However, in low light, the subject's background will come out ]. However, in low light, the subject's background will come out
darker than with [1/200-1/60 sec. auto]. darker than with [ darker than with
If [1/200-1/60 sec. auto] or [1/200 sec. (fixed)] is set, high-speed sync is
not possible in the <f> mode.
You can set the flash-sync speed for
flash photography in the aperture-priority
AE (f) mode.
[1/200-1/60 sec. auto 1/200-1/60 sec. auto
3 Setting Speedlite FunctionsN
221