Canon Speedlite EL-5 Advanced User's Manual page 181

Radio transmission wireless flash photography
Receivers do not fire or unexpectedly fire at full output.
Set the sender to <
Use the same settings for transmission channels and wireless radio IDs on the sender
and receivers (
Make sure receivers are within transmission range of the sender (
Run a transmission channel scan and set the channel with the strongest signal (
To the extent possible, position receivers within a direct line of sight of the sender.
Make sure receivers are facing the sender.
The camera's built-in flash cannot be used as a sender in radio transmission wireless
flash photography.
Pictures are overexposed.
When using autoflash with three firing groups (A–C), do not fire with firing group C
pointing toward the main subject (
When shooting with each firing group set to its own flash mode, do not fire multiple firing
groups in <
< > is displayed.
Set the shutter speed one step slower than the maximum flash sync shutter speed (
LCD panel illumination turns on and off.
The sender LCD panel turns on or off based on receiver (firing group) recharge status.
See LCD Panel
> and receivers to <
).
> mode that are all pointing toward the main subject (
Illumination.
).
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