Canon ST-E3-RT-V2 Manual page 31

7: FE Lock
FE (Flash Exposure) lock locks the correct flash exposure setting for
any part of the scene.
Perform FE lock by operating the camera. For the operations, see the
camera and flash's instruction manual.
If a correct exposure cannot be obtained when FE lock is performed, <Q>

blinks in the viewfinder. Move the receiver unit closer to the subject, open
the aperture, and perform FE lock again. You can also increase the ISO
speed when using a digital camera.
If the target subject is too small in the camera's viewfinder, FE lock might

not be very effective.
About Sender Units
You can use two or more sender units (sender units + receiver units =
maximum of 16 units). By preparing multiple cameras with sender units
attached, you can shoot by changing cameras while keeping the same
lighting (receiver units).
Note that when using two or more sender units, the color of the <D>
lamp varies depending on the order in which the power was turned on.
The first sender (main sender) is green and the second and subsequent
sender (sub-sender) are orange.
If the <D> lamp is red, the connection has not been established. After
checking the transmission channel and wireless radio ID, turn the power of
each sender unit off, and turn it on.
Using Fully Automatic Wireless Flash
31