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[OM] Vivitar 550FD M/P/O discussion

Subject: [OM] Vivitar 550FD M/P/O discussion
From: Joe Gwinn <joegwinn@xxxxxxxxxxx>
Date: Sun, 2 Jan 2005 12:00:55 -0500
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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