Canon EOS 20D Instruction Manual page 98

Using EOS-Dedicated, External Speedlites
U _ When using an external Speedlite retract the built-in flash before
mounting the external Speedlite.
If the EX-series Speedlite's firing mode is set to qFI-Lautoflash with the
Custom Function. the Speedlite will not fire.
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If autofocus cannot be achieved, the external EOS-dedicated
Speedlite's AF-assist beam (if the Speedlite has an AF-assist beam) will
be emitted automatically (except in <_> <_> <1_'3> modes).
The EOS 20D is a Type-A camera that can use all the features of EX-
series Speedlites.
Using Non-Canon Flash Units
Sync Speed
The EOS 20D can synchronize with compact, non-Canon flash units at
1/250 sec, or slower shutter speeds, With large studio flash, the sync
speed is 1/125 sec, or slower, Be sure to test the flash unit beforehand
to make sure it synchronizes properly with the camera,
PC Terminal
_ The camera's PC terminal is provided for flash units having a sync
cord. The PC terminal is threaded to prevent inadvertent disconnection.
4_, The camera's PC terminal has no polarity so you can connect any
sync cord regardless of its polarity.
_[_ _>,If the camera is used with a flash unit or flash accessory dedicated to
another camera brand, the camera may not operate properly and
malfunction may result.
_ Also, do not connect to the camera's PC terminal any flash unit requiring
250 V or more,
Do not attach a high-voltage flash unit on the camera's hot shoe. It might
not work.
]A Speedlite attached to the camera's hot shoe and a flash unit connected to
the PC terminal can be used at the same time.
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