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Question about the 600EX-RT - Optical slave mode


Hello.  I'm a long time Canon user and I'm pretty familiar with the gear, but my 600EX has got me stumped.  No matter what I do (and I have read and viewed the YouTube videos and gone through the manual until my eyes blur), I cannot get the 600EX to go into Optical Slave mode.  Everthing I'm reading is telling me there are four functions that show up when you press the wireless button and I should be able to go into wireless master, wireless slave, optical master and optical slave, but all can can ever see is the wireless.  I never see the lightning bolt in the upper right corner.  I only get the wireless antenna.  Normally, when I use the flash, it's attached to the camera as in regular use, but occasionally I need to use it off camera, and in one set up it works fine.  I bought a YONGNU-E#-RT II speedlite transmitter for when I want to fire the 600 off camera.  Simple... easy peasy... no problem.  Set the 600 to Slave and it gets triggered by the transmitter.  However, I have a couple sets of lights (Paul Buff Alien Bees 1500s) and (Godox MS300) that both use a transmitter and one set triggers 4 lights and the other triggers 2.  I want to use the 600 with the Godox as I'm doing a portrait shoot where the subjects are wearing uniforms and hats.  I want to set the 600 about 2 feet off the floor to fill face an eliminate the shadows that will come from the hat bill, and optical mode is the only way I can think of to get it to work.  Seems simple enough.  The 600 sees the light from the Godox and fires.  Can't get it to work because I can't get the 600 into the optical mode.  Canon says it will work.  The manual shows how to make it work.  My unit will not cooperate.  Any suggestions greatly appreciated.  This shoot is Feb 24.  Thanks.



Call Canon, the tech can get one and walk through it with you.

Wow.  That's your esteemed contribution?

@FhvnEd wrote:

Wow.  That's your esteemed contribution?

Well, I guess you can wait around and see if someone here has that model flash and can help you prior to February 24 or you can call the folks who do know and get straightened out.

John Hoffman
Conway, NH

1D X Mark III, Many lenses, Pixma PRO-100, Pixma TR8620a, LR Classic


It sounds to me that you are trying to get the 600 ex-rt to work as a dumb slave (what metz call servo mode) that will be triggered by detecting another flash, this is a function that it doesn't have.


It has an optical slave facilty that can be triggered by another Canon (or compatible) flash for use in ETTL master/slave mode but that is a different thing entirely.

If this is a 600EX-RT (mark I) then check the personal functions. P.fn 06 needs to be set to either 0 or 2 if you want to use optical slave or master modes.

P.Fn 06 set to 0 means both optical and radio master / slave modes are possible.
P.Fn 06 set to 1 (I think this is your case) means only radio master / slave modes
P.Fn 06 set to 2 means only optical master / slave modes

I think the original idea was that this would speed up switching between wireless slave / master modes, since you'd need to press the wireless button less times. Since I always use radio I set P.Fn 06 to 1, and it means that I can't accidentally set a flash to optical slave.
Brian - Canon specialist trainer, author and photographer


this may be old; the 600's optical is for communication with another Canon flash, not a true optical trigger from some other light source.  If you want a pure optical slave operation you will have to buy a detachable slave that is compatible with the flash.  That way any flash will trigger it.  the Canon flash should be set to manual of course, not Ettl.  Hope this helps.

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