Originally Posted by George Slusher
One VERY IMPORTANT caution, especially if you're looking for flashes on eBay. Note the "HV" in the model name. That can be critical. The 285HV is an update to the original 285. It has a lower trigger voltage (about 12 volts) that may be compatible with digital cameras and modern film cameras. (I wrote may because Canon says that many of its cameras don't like trigger voltages over 6 volts, so even the 285HV might be a bit too much on the camera hot shoe.
The original 285 (and its less-capable sister, the 283) has a very high trigger voltage, well over 100 volts. Putting a 285 or 283 on your camera could easily fry some circuits. Some radio triggers can't handle that voltage, either. The Pocket Wizards can handle up to 200 volts, so they can "insulate" the camera from a flash, even if the flash is connected to the same Pocket Wizard. (E.g., the PW is on the camera's hot shoe and connected to a flash via a cable.) I don't know about the receivers I got from jiakgong--their listing doesn't mention trigger voltage, though, given the "rough" translation they use, it might be hidden somewhere. The instruction sheet was in Chinese, but the little beasties are very easy to figure out. I have an old Sunpak flash that does have a high trigger voltage--I used it with my FM and, later, Minolta 35mm bodies, but I'm not willing to potentially fry an $18 receiver. You can contact MPEX to ask about the Cactus triggers they sell.
So, stick with the Vivitar 285HV or other flash that you can confirm has a low trigger voltage. Don't take a chance with your camera or triggers! You can check the trigger voltage for many flashes here. You can get "Safe-Sync" devices to protect the camera, as well. My approach, however, is to use the Vivitar flashes only off the camera. As I have a 580EX and Sigma 500 DG Super, I don't need to use the less-sophisticated Vivitars on my 30D.