Pentax 540FGZ - AF - Hot-shoe clip-on Flash Operating Manual page 46

When Using Both an AF540FGZ Attached to the Camera and a Separated Flash Unit as
Main Flashes
Use both flash units as main flashes
(Preparation of Flash Unit Attached to Camera)
1
Firstly, set the wireless mode and channel of the
flash unit attached to the camera, and register
them on the camera.
Attach the AF540FGZ to the hot shoe of the
camera after turning the camera off.
44
Set the power switch of the flash unit to
(WIRELESS).
Press the wireless mode button (M/C/S) the
number of times required to display MASTER
on the LCD panel.
Slide down the setting switch to the (yellow
dot) to display the channel on the LCD panel.
Press the channel button (CH) and select a
channel from 1CH to 4CH.