The situation: I have a 580EX on a lightstand and am firing it with Cybersync triggers. The transmitter is mounted on a 5D Mark II.
Because the camera is unaware of the transmitter, there's not a way to tell it to trigger on 2nd curtain. You can set the flash to 2nd curtain, but that doesn't do anything since the trigger just tells it when to fire.
Is there a way to accomplish a 2nd curtain fire with a setup like this? I'm trying to avoid buying $500+ worth of Radiopoppers.
No. Unfortunately the 5D2 does not allow 2nd Curtain Sync unless there is an attached to Canon EX compatible speedlite.
It's unfortunate as the only solutions seem to be workarounds, or expensive radio triggers.
If you are using Canon triggering systems, no you cannot perform 2nd-curtain sync over radio.
However, many third party radio triggers, like the Yongnuo YN-622c and Godox X triggers, can perform 2nd curtain by bypassing the Canon wireless protocol, and basically faking that the flash is on the camera hotshoe.
You can enable second-curtain sync (SCS) using a PocketWizard MiniTT1 or FlexTT5 mounted on camera and a further FlexTT5 mounted on the flash.
Whilst new these units still cost a small fortune new, there doesn't seem to be much of a secondhand market for them (presumably as people move over to Canon's RT flashes) and you can pick up a set on eBay for a very reasonably price — certainly sub-$500.
An added advantage is you can combine SCS and HSS. Obviously, you can't have both both simultaneously, but you can have a set up whereby SCS is enabled until you hit the camera's sync-speed (which I think is 1/200s for the 5DII) at which point the flash seamlessly switches over to HSS. It's a neat and rational set-up, particularly for fast moving variable situations such as photojournalism.
