Off camera flash 600ex-rt & 580 exii

Hi there, i am using my 600ex-rt on top of my 5d mkii as an optical trigger for my 580exii. The problem that i am experiencing is that my 600 on the camera keeps going off when i only want the 580 to flash. I have been through various settings but to no avail. I have had no problem with this in the past but i must have changed something on the camera or on the flash themselves. I have tried re-setting both camera and flash's plus the same thing happens on my 60d. Any help would be greatly appreciated.

Goto menu 2 and use the flash function button(left) so you get the flash icon w/o the flash beams in front. Note: the flash will still fire the optic transmission and could effect exposure but not too much, you'd need to use RT in order to prevent this.

Hi, thanks for the reply. I take it that for the infra red to work the flash on my camera has to fire to trigger the 580 ii remotely? I get what you are saying about RT. The flash fires in the optical mode but not in the RT mode. Thanks again.

The 600 uses a burst of visible light, not optical light, to trigger slaves. It will always fire when being used as an optical master. However, you can disable it from producing any illuminating light, as LMR said.

Check out the link in my signature for a tutorial on using Canon's wireless flash system.

Tiberius wrote in post #15898049
... not optical light...

That was a new one. Not even Wikipedia has a definition for that.

The master flash always fires at the moment of exposure, and you can't set it not to contribute to the illumination of the image. What you can do is to set it to contribute very little, by turning it "off". But still, if you set your camera to ISO 3200, the lens to f/1.4 and fire one meter from a white wall, that faint synchronisation flash which remains is all you need to expose that wall perfectly.

Gah. I meant visible light. Sorry.