I just read the old note from 7enderbender about using METZ 45 hammerhead flashguns on Canon Digital Cameras.
I agree 100% with his comments. Nice to see facts, not myths.
He/she quite correctly puts to bed all these stupid myths about "Frying" your DSLR.
If the Canon has a PC socket on the side then it is designed for a trigger voltage of 250V.
I have several METZ 45 CT flashguns and the highest trigger voltage on any of them was 25V.
I have a couple of very old, early and awful electronic flashguns with a trigger voltages of about 315V.
As an experiment I connected them to two old canon film camera and an early digital, all of which, according to Canon must not have more than 5 V on the hot shoe. No explosions, no fry-ups, nothing, just normal correctly times flashes. A trial of 300 firings resulted in no change.
In the old days of bulb flashes, the capacitor in the flashgun was connected to the bulb via the PC socket and there was a high current (probably at about 20V) and that would erode the camera contacts after time.
Electronic flashguns usually have a resistor in the trigger circuit (it only has to create a small discharge in the Xenon arc tube to create some electrons to initiate the main discharge.
Would I put my old 300V ringflash directly onto the hot shoe of my Canon 5D MKiii (rated at 250V)? No! Not when I can either use a radio receiver/transmitter to avoid connection or (as I have done) make a tiny optoisolator
circuit and fit it inside. I bought 10 optoisolators and 10 Triacs for less than £15. The circuit board measures about 0.9 in by 1 in and takes its power from the flashgun battery.
For those "nasty" flashguns (like old old studio flashguns) where I don't know what they are and have to connect directly by PC sync cable, I made a simple version of the circuit with a CR2032 battery (which is open circuit until the camera fires) and put it in a small box with a male and female PC lead.
I hope this:
a) makes it clear that 7enderbender was correct.
b) the reality is very different from the myth.