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
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|