This is a very common gear combination and has proven to be one of the biggest pains in life to get this working.  It shouldn’t be this hard.  I’ve seen a diver throw their camera on the ground and swim away from it because the strobe wasn’t doing what they thought it should.  I picked the same camera up and took pictures, no problem.

There are 2 core problems:

1.  The settings you need are poorly document and are not intuitive by any means.
2. The the camera and flash use optical TTL which most people don’t know even exists.  I myself had to experiment and reread old forum posts about different models.

Optical TTL is an interesting thing.  Most people know electrical TTL which uses waterproof electronic wires between the camera and the strobe.  In optical TTL, the camera turns on its own built-in flash, monitors the exposure that it’s shooting, and when it has received enough light, it turns off the on-board flash.  The strobe turns on when it receives light via the fibre optic cable, and turns off when there is no light coming through the fibre optic cable.  The signaling between the camera and strobe is a simple on-off instead of pre-flash and monitoring that most people are used to.

The Camera Setup:

Turn on TTL

Inside the main menu, second camera icon, choose “Accessory Settings” and set “Remote Flash” to RC.  This is an abbreviated form of “Remote Control”.  This turns on optical TTL.  Why they can’t call it TTL, I don’t know.

Second Camera Screen, Accessory Settings

Use the Right Flash Mode

Inside the quick menu (from shooting mode, hit the lightning button to the right of “OK”) there are 3 modes that you can use.

“Fill” works to turn on the strobe but without TTL: you manually adjust the strobe power.  “Fill” means that no matter what the camera meters the scene at, it should fire the built-in flash anyway, and this will trigger the strobe to fire.  Fill is designed to add light to foreground objects in an otherwise-lit scene such as people in the shade with a sunny background.

Fill Mode

“RC” Uses TTL and sends the start-stop signal to the camera’s built-in flash. “RC” only appears after you turn on “Remote Flash: RC” in the main menu as described above.

RC Mode

“Slow” fires the flash and keeps the shutter open, this gives more time for light to reflect off the background.  Think of it as “front curtain sync” if you’re used to flash on land.  I was unable to tell if the camera uses TTL for “Slow”.

Slow Mode

The Strobe Setup:

Use TTL

Turn the power knob to TTL.  Done.

Set to TTL.