Actionphoto wrote in post #10241577
I am trying to get my internal flash on a Canon 50D to trigger an optical slave attached to a remote 580 EX II. The 580 fires before the shutter opens.
Apparently canon fires a pre flash to let the TTL determine the flash exposure. However this sets off the 580 prematurely.
Is there any way of disableing this preflash. I cannot find anything in the custom functions.
Bob, there is no way to put the pop-up flash into a manual mode, thus disabling the pre-flash.
I believe there is a trick that some folks use to make the pre-flash occur and then have the flash wait for the main flash. Unfortunately, I do not know the trick. However, from what I can recall, this trick is not truly what I would call practical.
A far better solution for remote triggering of a flash unit would be to obtain a radio slave that can be triggered off either the hotshoe or the PC connector on your camera. There are some very inexpensive radio slave units - normally found on ebay - which would probably do well for you. I would not use the cheapie radio slaves for any paid work, though, as their reliability is not 100% especially when used over longer distances. For hobby photography, though, they are quite acceptable.
