Canon Wireless File Transmitter WFT-E7A Instruction Manual page 73

Do not use multiple flash units. Although slight, there is a difference in the shutter release timing
which may cause out-of-sync flash firing and inadequate exposure.
Linked shooting is not possible when master and slave cameras are set to [Mirror lockup]
[Enable] or [Enable:Mirror down w/ s].
During linked shooting, when you press the AE lock or depth-of-field preview button, the camera
adjusts the focus and meters as if you had pressed the shutter button halfway.
Once you have established a connection between the master camera and slave cameras, the
settings are retained even after you replace the batteries.
If you will no longer use a slave camera in linked shooting, set [Communication mode] to
[Disconnect] on that slave camera.
Any cameras compatible with linked shooting, when they have WFT series transmitters attached,
can be used as slave cameras, regardless of model.
Positioning the Slave Cameras
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