Paul C. Buff, Inc. Technical Forum

In some older film cameras, I think the flash sync switch was mechanical and was closed the entire time the shutter was open. Maybe the old ones with the FP sync socket.

With the newer models that have longer shutter speeds, say 30 seconds, does the flash switch remain closed the entire time? If it does, does that keep the flash unit from recharging for the next shot once it fires? (i.e. The flash cannot recharge again until 30+ seconds later once the switch reopens?).

I'm also curious as to how they do the rear curtain sync and if it is an electronically timed switch and maybe better suited to recharging the flash at the end of the 30 seconds.

Nothing is said about the shoe and its electronics and if it is prone to voltage issues off the flash itself.

Tia.

Mack

It seems that most cameras do keep the circuit closed the whole time. Generally, this should not be a problem, and not every camera seems to do this (I beleive it was a Fuji that didn't, but don't quote me on that). Just because the camera keeps the circuit closed, does not mean the flash cannot recycle.

Also, most camera companies define the maximum voltage allowed through the sync circuit. This does not ever seem to be below 6VDC, and most current DSLR's allow 240VDC. This can typically be found in the manual in the "notes" section on the page discussing the hotshoe and/or PC terminal or in the specifications page.

I imagine rear curtain sync is electronically timed, but I don't know for sure.

Thanks.

Someone gave me an old speedlight and it flashes, and then it buzzes until the shutter closed so I think it was trying to charge while the contacts were closed. Shutter closed and it got quiet. I doubt if it is red-eye fill ready or whatever that is in the menu as it is old and probably ready to be scraped. Oddly, it works fine with the wireless trippers, but I think those are instantaneous where the camera's hotshoe seems to be closed the entire time the shutter is open on slow speeds and it buzzes or whines inside the speedlight after it flashes.

For fun, I did take and ohmeter to the D7000 hotshoe and it must have some electronic switch and not mechanical as it shows some 8 megohm resistance in one direction and something different in the other. Works, but not like a mechanical switch as I would have thought inside it. I was looking for a clean open circuit on the center hotshoe contact to ground, but something (high resistance) is in there - unless the old flash smoked the body somehow.

Mack