Matt -- When the OM-4 (etc.) does a 1/2000 exposure (0.5 milliseconds) the
duration of the actual shutter curtains travel (the time for the curtains to
travel across the film) is the same as for any other exposure. The slit
width (the space between the first and second curtains) is such that any
portion of the film gets only 1/2000 second of light, but the actual total
length of exposure from the first bit of the image to the last bit of the
image is ~1/60 second. The curtains take at ~15 milliseconds to cross the
film plane opening, and the F280 flash is going off every 0.125 milliseconds
during that time... so there are about 50 or 60 flashes during the time of
the shutter curtains travel across the film plane.
You might see some strobing effect on fast-moving subjects (like hummingbird
wings) but with the multiple light bursts the effect is mostly as if there
was one flash of a long enough duration to allow the whole curtain travel
time to be illuminated. The F280 mimics the old "FP" flashbulbs, those had a
long sustained burn time, during which the focal shutter plane curtains
could cover the whole film area.
--
Jim Brokaw
OM-'s of all sorts, and no OM-oney...
> From: Matt BenDaniel <matt@xxxxxxxxxxxx>
> Reply-To: olympus@xxxxxxxxxxxxxxx
> Date: Sun, 27 Apr 2003 19:50:32 -0400
> To: om@xxxxxxxxxxxxxxxx
> Cc: olympus@xxxxxxxxxxxxxxx
> Subject: Re: [OM] F280 FP
>
> Skip,
>
> I found an interesting article here:
>
> http://www.rit.edu/~andpph/text-streak.html
>
> Apparently in Super FP mode, the F280 pulses about 10000 Hertz. This implies
> that the F280 would flash 5 times during a 0.5 millisecond exposure. That
> does not sound equivalent to continuous lighting. For example, with moving
> hummingbird wings, this could yield some interesting artifacts.
>
> It's also too bad that the engineers didn't make the F280 capable of
> delivering a very bright duration of a few milliseconds that supports a
> shutter speed of 1/2000s with a reasonably strong guide number.
>
> Matt
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