You are correct in many ways.
Back when the databacks were plugged into the PC socket, you would have to set
an OM-2 to FP-sync to assure firing the back since the safety switch in X-sync
would prevent triggering at any speeds above 1/60th second. An OM-1 would fire
the back or flash at any speed so no special settings were necessary.
When Olympus built the databack contact into the body of the OM-2n (for use with
the Databack 3 or 4), it was controlled by a special "P Circuit" which triggered
the databack indpenedent of the flash. (This may have been timed similar to
X-sync -- I think you can see the LED's of a databack "blink" if you look
through the lens mount when you fire the shutter at 1/60th -- but you'll need to
confirm that.)
The OM-1n used a separate switch similar to the FP switch that operated off the
mirror lifting mechanism. I'm sure the timing has factory perimeters but since
there's no critical timing they've got to be pretty wide. In fact, I have
never, and I stress _never_, had to change or even repair that feature.
The sync of the OM-4/2s/3/PC, et al, is controlled electronically. In other
words, the flash is fired by an IC that sends a pulse to an SCR rather than
simple blade switches closing. The triggering of the databack contact is a
mystery to me. Like the switch on the OM-1n, I've never encountered a problem
with that function on a 4/etc., so I've never studied the circuitry involved.
In fact, I can't find anything about it in Olympus' manuals! At a glance I
suspect the data print is initiated in relation to the closing of the main
switch, but this is clearly a fixed relationship -- there is no adjustment.
Back to cases, though -- If you're going to actuate a digital back, I believe
you're going to want to just use the X-sync timing at 1/60th second (or longer)
anyway, won't you? 1/60th second is the fastest speed where the entire focal
aperture is open at once, and X-sync will then close to fire a flash (or record
an image). Any faster speed and you'll have one of the shutter curtains in the
way when you record the image, and any other sync setting and you'll risk
recording an image before the shutter even opens.
Now, whether the circuit of a camera like an OM-4 would provide an appropriate
signal to activate a digital back or not, or if a "mechanical" device like an
OM-1 or OM-1n would be preferable, I don't have any idea -- but I bet someone on
the list will venture an opinion!
Julian Davies wrote:
> For OM1 / 2 the documentation of the data backs says "set the sync to FP and
> attach the cord". I can see that FP is necessary to get the data back to
> trigger at speeds above X sync, but the timing should be otherwise
> uncritical.
> With the 2n and above, the additional complication of auto X sync selection
> and the data - back trigger contact are introduced.
> Then we get to 2s/3/4 and FP isn't an option.
> I presume that on the 2n, there is an additional microswitch to make the
> contact to the Data back trigger. I also assume that this switch is not
> factory set to any particularly critical timing. Does anyone know if these
> are valid assumptions? How about on OM4(Ti) with electronic switches?
> The reason I would like to know is that the trigger contact could be used
> for more interesting purposes if the timing were predictable, notably for
> triggering the "shutter release" of a digital sensor. With the used price of
> early digicams being close to nothing now, I'm considering stripping one and
> making a digital back for the OMs. It was pretty simple to make an Izone
> polaroid back, so this shouldn't be too hard, provided I can produce a
> viable trigger.
> Just need to find a crappy digicam with the physically largest sensor
> possible! Any suggestions?
> And a standard back with a truly dead pressure plate but good hinge and
> lock. Last time around I really struggled to find one which was a 'cutting
> up' candidate. Oly just made them too well!
>
> Julian
>
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