I have a problem using the high speed sync feature on my 430ex that I use with my Canon T3i body. When the flash is mounted on the camera and the high speed sync feature is on, I can shoot as fast as I can without any problems. However, when I use the flash off camera (I use the promaster wireless hot shoe), even with the high speed feature on, I can only shoot up to 1/350 before I start to see the curtain creep up into the picture.
Why does this happen? Do I need to be using a different wireless hotshoe?
In order for High Speed Sync to work off camera, the flash must have full ETTL communication with the camera. One way is to use the Canon wireless Master/Slave system with a 580Ex II or ST-E2 "Master". Another way is to use an Off Camaera Shoe Cord like the Canon OC-E3.
There are also 3rd party wireless radio triggers that can provide ETTL and High speed sync.
I am not familiar with the "Promaster Wireless Hot Shoe" but I suspect it does not give you the necessary ETTL communication.
The 430EX II can handle high-speed sync. But the "problem" is that the on-board pop-up flash cannot handle high-speed sync. This is why it works when the 430 is on the camera body, but does not work off-body.
It would work off-body as well... if only the on-camera trigger ALSO supported high-speed sync.