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From: jmuchow@SPAMMENOTcamlight.com (John Muchow)
Subject: Re: Camera Flashes
Date: Tue, 03 Dec 2002 18:42:09 GMT
Organization: MindSpring Enterprises
References: <email@example.com> <firstname.lastname@example.org>
X-Server-Date: 3 Dec 2002 18:45:57 GMT
X-Newsreader: Forte Free Agent 1.21/32.243
>>>The flash really is triggered by shorting the PC cable, right? I can fire
>>>it by shorting the connector, and it works fine when the PC cable is in my
>>>camera, but if I manually short the end of the cable nothing happens. I
>>>really don't know why.
In my experience, yes. If the cable is functioning properly and the
flash has recycled, I can't think of any reason why shorting out the
cable wouldn't fire the flash. There must be something weird in the
layout/arrangement of the parts of the cable's connector that makes it
hard to reach them properly to short together.
>>>What kinds of voltages and current would be running down the cable for an
>>>old flash like the Vivitar 2600 or 2800? The rep said something about 150
>>>volts, but I find it hard to believe there's 150 volts across the signal
>>>and ground of the cable and being fed into the camera.
Very high voltage isn't uncommon for older flash units. This is the
reason why I had to come up with my "buffer" circuit because the high
sync voltage of some flash packs was frying the sync circuits in the
more delicate electronic cameras.
The current varies but in my experience it's usually been a
discharging capacitor that supplies any current flowing through the
camera's sync circuit.
>>>How does the hot shoe work? I can slide the flash unit into a metal
>>>bracket and it won't fire, so it seems the shoe mount isn't triggered by
>>>shorting the connections. Is there some voltage applied across the
>>>terminals? I didn't want to experiment too much for fear of putting too
>>>much voltage the wrong way through it.
The camera sync circuit is just paralleled with the hot-shoe contacts.
There can be other contacts for additional auto-exposure features, but
two of the contacts should short together when a picture is taken.
AFAIK, no voltage is applied to the hot-shoe contacts by the camera.
Your unit may not be compatible with the camera's flash shoe. Though,
I thought that any flash unit would work in any shoe (but perhaps
without certain features that would only work when a same-brand camera
and flash were used together). There is probably a contact that is
not touching another properly or a portion of the camera's sync
circuit may be damaged.
What is the open-circuit voltage across the flash unit's sync
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