Won't synchronize using slave

I was using external (off camera) strobes plus flash on the camera as fill. Whenever I connect a slave unit to the strobe, it won't synchronize. But if I connect my radio control trigger (Mine is the old type, thus it still has the pvc connection) it seems to be alright. Can't understand why. Anybody knows the cause?

Optical slave? If so its probably fooled by the preflash of the flash on the camera and fires early. What flashes, what kind of slaves, and what mode are they in?

gonzogolf wrote in post #13775334
Optical slave? If so its probably fooled by the preflash of the flash on the camera and fires early. What flashes, what kind of slaves, and what mode are they in?

I believe it's an optical slave. The external flashes are Lumedyne heads. Flash on the camera is EX580. It also seems that it the flash on the camera didn't synchroned either.

eaglesnest wrote in post #13775360
I believe it's an optical slave. The external flashes are Lumedyne heads. Flash on the camera is EX580. It also seems that it the flash on the camera didn't synchroned either.

If the flash on the camera is in ETTL mode, it emits a preflash (used to calculate exposure) just prior to the flash, so close you dont even know its there. That will cause the slaved flashes to fire early before the shutter opens. Try putting the on camera flash in M mode.

gonzogolf wrote in post #13775375
If the flash on the camera is in ETTL mode, it emits a preflash (used to calculate exposure) just prior to the flash, so close you dont even know its there. That will cause the slaved flashes to fire early before the shutter opens. Try putting the on camera flash in M mode.

Bingo!! synchronized perfectly after I put the camera flash in "M" mode. Thanks a lot.