Canon Speedlite 90EX - Manual (Page 14)

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To save battery power, power will be turned off automatically after 5 min. of idle use. To turn
on the power again, press and hold the Speedlite’s power button for at least 1 second.
* Canceling the auto power off function is possible. (p.14)
When you press the camera’s shutter button halfway, the flash may fire repeatedly. This is
the AF-assist beam function that facilitates autofocus for dark scenes. Its effective range is
approximately 2.8 m/9.2 ft.
This function is available when using the Speedlite with an EOS DIGITAL camera that has an
external flash control function. Depending on the camera model, note that the firmware may
need to be updated.
During wireless flash shooting, the 90EX will not fire as AF-assist beam.
Other Functions
Auto Power Off
AF-Assist Beam
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