I want to drag the shutter (second curtain sync) on my Canon 50D using either a speedlight, or via a wireless remote flash.
The 580 EX/EXII will trigger when the shutter opens, and again when it closes. I only want the second flash before the shutter closes, I don't want the first (e-TTL?) flash.
Secondly, I can't find a method of setting second curtain with a Pocketwizard attached.
Any suggestions?
Unfortunately there is no way to get a Canon DSLR to actually send the flash signal when the shutter is about to close! Canon flashes know the shutter speed so they can delay the firing. When using a flash that doesn't talk to the camera you can't get second curtain sync. However, when using a Pocketwizard, you can set the Pocketwizard to add the appropriate delay to get the flash to fire with the second curtain (I think only some models e.g. Pocketwizard multimax allow this).
When set to second curtain sync the first flash is actually before the shutter opens and is for metering purposes (e-TTL as you suggest). To turn this off you'll have to use the flash in manual mode.
There's custom function in some Canon models (I think 30D and 1Dm2 has it):
"15: Shutter Curtain Sync (Flash Mode) is how you select rear-curtain sync to make moving objects look like they're moving in the right direction, presuming you're using a slow shutter speed in Tv, Av or M modes.
0: 1st curtain: Flash fires as soon as the shutter opens.
1: 2nd Curtain: Flash fires at the very last instant of exposure. If a subject is moving and making a blur under ambient light, the final image will have the subject stopped with a ghost flash image at the beginning of the blur. This results in a sharp image with blurs behind a moving subject, implying speed. The default above (same for all cameras) puts the blur in front of a moving object, which looks silly."
Found from: http://www.kenrockwell.com/canon/30d/custom-functions.htm
I think you're confusing the pre-flash as two bursts of flash. There is only one flash burst that actually exposes the photograph.
The initial burst you may have seen is just to allow the speedlite to measure the reflective surface, and distance of the subject you're photographing.
The initial flash is typically fired at 1/32 power on the 580EXII.
But back to your question, 1st and 2nd Curtain Sync and HSS can only be selected when a speedlite is fitted or connected to by a hot shoe cord.
Pocket Wizard TTL Flex systems allow the photographer to shoot at higher sync speeds, e.g., 1/8000 sec, but for an extortionate price.
1st curtain sync is the default option on most if not all Canon equipment.
