At 3:52 AM +0100 1/2/05, Listar wrote:
>From: "Wayne Culberson" <waynecul@xxxxxxxxxxxxxxx>
>Subject: [OM] Vivitar 550FD M/P/O discussion
>Date: Sat, 1 Jan 2005 16:42:37 -0400
>
>The following is part of a discussion Chuck Norcutt and I've been having off
>list about some uses and safety issues with Vivitar 550FD
>Minolta/Pentax/Olympus dedicated flashes. I think our discussion started on
>the Vivitar or Kiron lens list. (Chuck had recommended these flashes some
>time ago, so I've been watching for one on the auction site.) I thought
>maybe someone here might be able to offer some insight, providing of course
>anyone has the patience to read all this below....
A few things occur to me.
1. Voltage measurements at
http://www.botzilla.com/photo/strobeVolts.html seem to vary all over
the place, which I suspect is due to the various kinds of voltmeters
people have. Many synch circuits consist of a capacitor charged
through a large resistor, with 1 megohm being common, so the
voltmeter impedance must exceed 10 megohms for reasonably accurate
measurements. Many cheap voltmeters have far lower impedances, and
will load the synch circuit down, causing false readings. And, one
must wait for the voltage to stabilize.
2. ISO standards (ISO 10330 "Photography -- Synchronizers, ignition
circuits and connectors for cameras and photoflash units --
Electrical characteristics and test methods," 1992; this may be in
the process of revision) do carry considerable weight in the photo
world, but are not retroactive. This means that the next generation
will meet the 24-volt standard, but current production is what it is.
I hope and assume that this ISO standard also makes the manufacturers
all use the same polarity.
3. I doubt that shorting the TTL pins on Olympus (or anyone else's)
flashes will cause any damage, as a flash that wouldn't work (let
alone would be damaged) in a plain old one-contact metal hotshoe
would be laughed out of the market. That said, if Olympus went to
the trouble of mechanically retracting the extra pins, it may be that
shorting those pins will interfere with flash operation.
4. It's probably OK to parallel flashes that have the same
low-voltage polarity (plus or minus) on their synch terminals, even
if the voltages are not exactly the same, so long as the voltages are
all no more than 10 or 15 volts. If the polarities are opposite, the
units will likely keep each other from working, but probably won't
hurt each other. But, no manufacturer will guarantee this, because
they cannot test all combinations, and are responsible only for their
own products.
Joe
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