Joe wrote:
>>If the voltage is less than twenty volts, and the same polarity as OM
>>flashes, you're OK on all OM bodies. If the voltage is more than twenty volts
>>(a hundred or more being typical), the flash can be used only on the OM-1 for
>>sure. I don't know about the OM-2, but the OM-3 and OM-4 are out.<<
This is a popular misconception, pretty much all the OM's take high voltage
triggers.
The OM2 service manual says the mechanical flash trigger switch has a test
voltage of 500V. The OM2N uses a 1N4004 diode to isolate the mechanical switch
and the diode is rated at 400V. The OM2S,OM4 and OM4Ti all use a high voltage
thyristor (scr) trigger which is good for all modern high voltage flashes
(which run < 330V). Some really old studio units and Metz mech vibrator units
used 500V but even old Sunpak units like 611 (international version Autozoom
5000) or the old manual Sunpak ringflash are less than 300V. I assume the OM3
also uses a thyristor, but I have not verified this. In the OM4 it is mounted
up near the eyepiece.
Because of the thyristor or diode in OM2N and later devices polarity of trigger
voltage is important for triggering. In Om1 or OM2 it does not matter.
As mentioned on this thread, measuring the high voltages is often inaccurate
because of voltmeter loading. A flash like the 611 has sync pin charge resistor
in excess of 1MOhm, giving rise to quite bit more han 10% error with a typical
digital voltmeter and much more with an analog meter.
Regards,
Tim Hughes
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