Canon EOS M Instruction Manual page 316

Troubleshooting Guide
Even though I set a decreased exposure
compensation, the image comes out bright.
Set [A3: Auto Lighting Optimizer] to [Disable]. When [Standard], [Low]
or [High] is set, even if you set a decreased exposure compensation or flash
exposure compensation, the image may come out bright (p.159).
When I use the <f> mode with flash, the shutter speed
becomes slow.
If you shoot at night when the background is dark, the If you shoot at night when the background is dark, the shutter speed If you shoot at night when the background is dark, the
becomes slow automatically (slow-sync shooting) so that both the becomes slow automatically (slow-sync shooting) so that bo becomes slow automatically (slow-sync shooting) so that bo
subject and background are properly exposed. To prevent a slow subject and background are properly exposed. To prevent subject and background are properly exposed. To prevent
shutter speed, under [A1: External Speedlite control], set [Flash
sync. speed in Av mode] to [1/200-1/60 sec. auto] or [1/200 sec.
(fixed)] (p.221).
The flash always fires at full output. The flash always fires at full output. The flash always fires at full output.
If you use a flash unit other than an EX-series Speedli If you use a flash unit other than an EX-series Speedli If you use a flash unit other than an EX-series Speedlite, the flash will
always be fired at full output (p.293). always be fired at full output (p.293). always be fired at full output (p.293).
Under [A1: External Speedlite control], if [Flash metering mode]
under [Flash C.Fn settings] is set to [TTL], the flash will always fire at Flash C.Fn settings Flash C.Fn settings
full output (p.224). full output (p.224). full output (p.224).
I cannot set flash exposure compensation with
[Flash function settings].
If flash exposure compensation has been set on an external Speedlite,
[Flash exposure compensation] (p.223) cannot be set in the [Flash
function settings] screen. Also, if you set flash exposure
compensation with the camera and then set flash exposure
compensation with the external Speedlite, the Speedlite's flash
exposure compensation setting will be given priority. When the
Speedlite's flash exposure compensation is canceled (set to 0), [Flash
exposure compensation] can be set with the camera.
316
1: External Speedlite control 1: External Speedlite control
1: External Speedlite control 1: External Speedlite control
1/200-1/60 sec. auto 1/200-1/60 sec. auto
shutter speed shutter speed