The curtain speeds should be set first so they are the same (consistent
slit width), then high speeds are set using the trigger adjustment.
Changing the curtain speeds makes high speeds uneven. It may be 1/2000 in
the center of the frame but at the opening edge it might be 1/1500, on the
closing edge, 1/3000 (or the slit could close completely. )
0.5 ms is ideal but rarely are the speeds exact (in any camera, any brand).
John
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----- Original Message -----
From: wayne <wayne@xxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Thursday, September 23, 1999 4:02 PM
Subject: Re: [OM] F280
> At 11:32 AM 9/23/99 +0200, H@nz wrote:
> >(and also provides some insight in the accuracy of the manual shutter
> >speeds. Aaargh 1/1400 instead of 1/2000?):
>
> Typically for an untuned OM-4t. The top shutter speed needs to be tuned
> periodically, in my experience. Maybe John can give us some typical
> guidance. Most people don't shoot at 1/2000 very often, so most don't
> notice that it is off. My guess is that 1/1400 .vs. 1/2000 maybe only
> one or two clicks on the shutter curtain tension adjustment screws.
>
> >SET MEASURED SLIT FLASH
> >TIME TIME WIDTH,mm DURATION
> >
> > 1/60 1/64 >36 1/27
> > 1/125 1/130 26 1/35
> > 1/250 1/260 13 1/41
> > 1/500 1/550 6 1/45
> > 1/1000 1/890 3.5 1/46
> > 1/2000 1/1400 2 1/45
>
> The variation in time may simple mean that the time it takes to meter
> OTC before releasing the 1st curtain is on the order of the required
> shutter speed. For example, it takes 1/60 second of OTC metering to
> derive a 1/60 speed => flash duration of 1/60 + 1/60 = 1/30. The flash
> duration needs to remain on for at least 1/60 second to cover the
> complete curtain travel. OTC metering of 1/125 second would give: 1/125
> + 1/60 = 1/40, similarly, 1/250 + 1/60 = 1/48, 1/500 + 1/60 = 1/53,
> etc. plus a little extra for other response times gives a pretty close
> number to the above flash duration measurements.
>
> So the operation scenario would be (OM-4Ti + F280 in Super FP):
> - The flash starts to emit stroboscopic light pulses
> - The OTC meters for the approximate duration of the required shutter
> speed.
> - then the 1st curtain is released
> - the 2nd curtain is released based on OTC exposure measured above
> - the flash remains on for the duration of the 2nd curtain travel
> - total time = 1/speed + 1/60 + tolerance and shutter release response
> time.
>
> Having an initial OTC metering time on the order of the required
> shutter speed makes since for an integrating light sensor. This is
> probably normal camera behavior for all auto exposures. For example,
> exposures longer than 1/60 (not talking FP flash, just OM-4T camera in
> auto with lens and available light), the metering is probably an
> initial 1/60 OTC, release the 1st curtain, continue integrating meter
> OTC+OTF to required exposure, release 2nd curtain. The travel time of
> the 2nd curtain balances the initial 1/60 second of OTC metering.
> Faster than 1/60 speeds are the same as describe above for super FP
> flash, except that available light is used (ie. no strobe light). So,
> to the camera, the Super FP mode is no different than having a flood
> light. Except that the the F280 Super FP flood light runs outta gas in
> 1/25 second - long enough for 1/60 and above camera operation.
>
> Wayne
> Hopkinton, MA
>
>
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