Canon ST-E3-RT-V2 Manual page 48

Linked Shooting
Shooting with manual focus is recommended for the receiver unit

cameras. If focus cannot be achieved with autofocus, linked shooting is
not possible with the corresponding receiver unit camera.
There is a short time lag between the release of the receiver unit camera

and the release timing of the sender unit camera. Perfectly simultaneous
shooting is not possible.
If you fire multiple flash units at the same time during linked shooting, the

appropriate exposure may not be obtained or uneven exposure may
result.
When [Flash firing] in [Flash function settings] is set to [Disabled]

(p.52), linked shooting cannot be performed.
When performing linked shooting in the Live View state, set [Silent LV

shoot.] on the sender camera menu to [Disabled]. If [Mode1] or [Mode2]
is set, the receiver unit cameras will not be released.
The transmission distance may be shorter depending on the conditions

such as the positioning of receiver units, the surrounding environment
and weather conditions.
The linked shooting function is the same function as the linked shooting

featured by the WFT series of wireless file transmitters. However, linked
shooting cannot be performed in combination with the WFT series.
Moreover, the release time lag differs from linked shooting performed
using the WFT series.
You can use this function as a sender unit remote control for linked

shooting without attaching a Speedlite or transmitter to a camera. When
function button 1 <U> on the sender unit is pressed, all the receiver
unit cameras are released.
During linked shooting, the time until auto power off takes effect is 5 min.

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