Old 430EX won't sync with 5Diii when used off camera, if shutter speed is over 200.

[paubaker]

I am using a cowboy studio transmitter & receiver.  Manuals for the 430 & 5d both indicate highspeed sync will work with higher shutter speed.  430 is set to highspeed sync.

[Skirball]

The Cowboy Studios won't allow HSS.  I'm not sure what model you're using, but knowing Cowboy Studios I'm guessing it's full manual only. The Yongnuo 622 triggers will allow HSS.

Again, I don't know the specifics of your trigger.  But Yongnuo manual triggers (602, 603) will still trigger if you go above max sync speed, you'll just get banding due to the falling shutter.

Keep in mind that HSS significantly reduces the amount of power out of a flash.  And since it's effectively a continuous light at that point, the faster the shutter speed the less the flash can contribute to the exposure.  I'm not sure what speeds you're using, but if you're up in the 1/1000+ range the power output will be quite small.

[paubaker]

Thanks so much. That was extra helpful! 🙂

[Skirball]

No problem, glad I could help.

To elaborate a bit on my middle paragraph.  The Yongnuo manual triggers (and probably yours) do nothing other than send a signal to the flash to fire.  There's no feedback, so if my flash is on manual it'll fire regardless of the shutter speed.  But it'll only light up a fraction of the frame because the shutter will block it for part of the flash. 

However, I don't know what happens if I use a manual trigger and turn my flash to HSS.  Never tried it, but I'd guess that it just won't fire.  I suppose it could go back to manual or a low-power HSS, but in general HSS requires feedback from the camera to tell the flash how long to fire for.