You should have no concern about flash voltages on OM cameras. Here's
the true skinny in some old posts from Tim Hughes.
Chuck Norcutt
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Date: Wed, 10 Nov 2004 04:52:09 -0800 (PST)
From: Tim Hughes <timhughes@xxxxxxxx>
Subject: [OM] Re: E-1 and OM System flash units?
Chuck,
The Om2S and OM4's use a sensitive gate, high voltage thyristor switch,
so can easily withstand the <330V on the flash contacts (typ more like
200V for m,any flashes) .
The Om1/2 uses mechanical switch with test insulation of 500V according
to service manual. The Om2N uses mechanical contact isolated by 1N4004
(400V ) diode. Anecdotally people on this list have reported damaging
OM4 in the rain with high voltage flash. I am skeptical that this
actually happened.unless somehow camera ground came adrift from ccts,
since the leakage path would have to get to one of the ic's which are
isolated from the thyristor gate by a capacitor (from memory). On the
other hand water could easily cause other leakage problems as the
insulation requirements for the photo-sensors etc are extremely high.
(probably > 100M Ohms)
Regards,
Tim HGughes
Date: Sun, 2 Jan 2005 21:44:15 -0800 (PST)
From: Tim Hughes <timhughes@xxxxxxxx>
Subject: [OM] Re: Vivitar 550FD M/P/O discussion
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
Date: Wed, 5 Jan 2005 14:11:02 -0800 (PST)
From: Tim Hughes <timhughes@xxxxxxxx>
Subject: [OM] Re: Vivitar 550FD M/P/O discussion
This topic seems to always get recycled, so I don't like to see it get
recycled with misinformation.
Joe wrote contesting the high voltage capability of the OM4 trigger cct:
>>>>The OM-4Ti circuit diagram does show the SCR (Q110), and the
inspection criteria does list 500 volt insulation resistance. But I
haven't figured out how transistor Q101 figures in, and why it
doesn't let the 500 volts into the big IC (IC102). I doubt IC102 can
handle any such voltage.<<
Joe , Oly uses a rather small triangle to indicate chassis ground. The
emitter of Q101 you assume is possibly tied to trigger high voltage, is
grounded to chassis, The OM4T service manual shows one line less
connected to the FP switch cct +pc socket ,than shown on OM4, making
this more confusing, but this does not change the connection to ground
of Q101 emitter. The OM4 **main** schematic diagram is clearer, and
page E-48 of the OM4 service manual makes it much clearer, especially
the lower assembly diagram. (unfortunately some other diagrams in Mark's
scan of OM4 are largely illegible) Q101 discharges C103 through
thyristor gate to chassis, to trigger it. It needs to be set up to do
this because the 3V battery is otherwise the wrong polarity to trigger
scr gate without the +ve level shift provided by capacitor. The OM4T has
a slightly improved C103 charge cct for the capacitor using an added
diode.
I always wondered about the FP switch. I assume this is how it is meant
to work: Because Oly wanted to allow external flashes to be used via the
pc-sync socket, but wanted compatibility with on camera T series
flashes, they added the FP switch timed so it opens just after the
trigger is applied to scr. That way the scr has already shorted out the
Tseries flash trigger and so no high voltage can be applied to the T32
trigger pin by the external flash at time when FP switch closes. When
only an external flash is connected via pc-connector, the trigger pulse
is long enough to still trigger the scr+external flash. Very Obscure
Warning : This means if you use a high voltage flash and connect it via
a hotshoe to pc-sync adater you could apply a high voltage via the
Tseries/F connector to an Oly system flash. (The hot shoe sync terminal
goes directly to the Tseries 5pin connector, not via FP switch as it
does for pc connector.) If it works as I assume, it also means by
shorting the hotshoe sync pin to ground the external pc-socket should
trigger an external flash even when the camera is set to red manual 1/60
with no battery It would be interesting to see if it also works like
that on an OM3, as this would allow flash with dead batteries or in very
cold conditions whiich is not possible normally.
An interesting bit of flash trivia for the OM4 is that on manual speeds,
it will trigger strobes at any shutter speeds (with poor results >1/60).
It makes a bit more sense on OMT with possibility of super fp, but even
there, since the super fp needs the extra dedicated pins, it is strange...
As noted before the only single digit Om I have not checked for high
voltage capability is OM3 but my guess is its design is similar to OM4,
esp as it requires a battery to fire. We need to get a schematic to verify.
As far as 2digit OM's, the OM10 seems ok, as is the OMPC/40, but I have
not checked others.
Regards,
Tim Hughes
----------------------------------------------------------------
keith_w wrote:
> I don't know whether there are any folks here that still use Practika flash
> nits, but...I'll ask anyway.
>
> A friend has a Practika BD-24 tilt head flash she wants to use on an Olympus
> OM-2n. (More hybridization, right?)
>
> Anyhow, the question arises, what's the trigger voltage in that Practika, and
> how much voltage can the Oly safely accept?
> Thing is, I know of no hybrid camera list, so I'll start here, and hope
> someone can come up with a site or two that might cover those answers.
>
> Thanks for the time.
>
> keith whaley
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