Flash won't snyc with non TTL flash

[Tshoe]

I am trying to use a Sunpak 611 flash with a slave which is fired by a 550EX and a Digital rebel. The flash fires but there is no effect on the picture from it. Can anyone answer this?

[robertwgross]

In normal flash modes, your camera tells the 550EX to flash. The 550EX puts out a pre-flash, which the camera uses for metering purposes, and then puts out a main flash which actually does the job.

Your slave flash is seeing the pre-flash and is firing then, before the actual main flash and sensor exposure.

---Bob Gross---

[scottbergerphoto]

Robert is right as usual. You need to use a Digital Slave such as one from Wein that will ignore the preflash. The other option is to use the 550EX on manual. There is no preflash in manual. Then you lose ETTL. You can use GN's or a flash meter.
Scott