Canon Speedlite 470EX-AI Instruction Manual page 104

Troubleshooting Guide
Optical Transmission Wireless Flash Photography
The receiver unit does not fire.
Set the receiver unit to <:x> (p.74).
Set the transmission channels of the sender unit and receiver unit to
the same numbers (p.74).
Make sure the receiver unit is within the transmission range of the
sender unit (p.72).
Point the wireless sensor of the receiver unit toward the sender unit
(p.72).
Position the receiver unit at a location with the clearest possible view
of the sender unit.
If the sender unit and receiver unit are too close, the transmission
may not take effect properly.
When using the camera's built-in flash as the sender unit, raise the
camera's built-in flash, and set [Wireless func.] on the camera's
[Built-in flash func. setting] screen.
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