Piers,
Your idea works. I simply taped a piece of white paper in front of the sensor.
When the T32 is set on auto (even f8) it gives off the briefest of flashes,
even when the scene is distant and dark. Without the paper, the T32 yields a
big blast. With the paper, the flash may be as brief as 1/50,000s.
I'm looking for a way to a 1/8000s flash. My guess is that I'd get that at
1/16th power, and that would be GN 2 (meters ISO 100). If I set the auto to f4
and position the flash 0.5m from the target (e.g. a midtone plant) it should do
that. I can double check with a flash meter.
Matt
At 14:17 25-04-03 +0100, Piers Hemy wrote:
>To get the minimum flash duration out of an auto flash, Matt, seems to me
>you need simply to put a small reflector in front of the sensor to 'scoop'
>some of the flash out put straight back into the sensor.
>Thus what the sensor thinks is the flash-subject distance is a half inch or
>so, although the bulk of the output goes way past that.
>What the duration would be... I don't know for sure, though I am pretty sure
>it will be the minimum possible - but you have the flash metering capability
>to get the exposure right, at least.
>HTH!
>
>Piers
>
>
>-----Original Message-----
>From: owner-olympus@xxxxxxxxxxxxxxx [mailto:owner-olympus@xxxxxxxxxxxxxxx]
>On Behalf Of Matt BenDaniel
>Sent: Friday, April 25, 2003 12:49 PM
>To: olympus@xxxxxxxxxxxxxxx
>Subject: [OM] Fast Bright Flash
>
>
>I'm planning to shoot hummers later this month.
>
>One of the ways to stop wing motion is to use very bright fast flash. I'm
>NOT going to use TTL (cost and nonpredictability). I have four optically
>slaved Vivitar 283's with VP1's. Each 283 is powerful flash (GN 120 feet),
>but the trick is to use all of them in manual mode at a fraction of its
>power (1/8th or 1/16th), because that yields a very short flash (on the
>order of 1/8000th second or faster). Overall brightness is achieved by using
>multiple flash units (and the more the merrier) very close to the subject (2
>feet).
>
>The camera lens will be stopped down to about f/32 (for depth of field)
>using ISO 100 film, and I'll try to shade the subject from direct sunlight,
>in order to reduce ghosting. I'm shooting with an OM-4 synced at 1/60s.
>
>My question is whether I can supplement the 283's with slaved T20's or
>T32's. The problem is that if any of the flashes have a longer duration, the
>edges of the wings will be blurred. On the T32 in particular, there is a
>manual setting that uses 1/4 power. The question is: how long is that flash
>duration? I've looked in manuals, Olympus source books and the web but
>cannot find any such info. The nominal flash duration of the T32 is states
>as "1/50.000~1/1000 sec", but that says nothing about how to predict/control
>the duration.
>
>I know I can get an even shorter flash duration out of the T32 or T20 by
>using it in auto mode. By varying the distance of the flash to the subject,
>I can control how much light any single isolated unit would put out. But
>when there are multiple flashes being used, I'm less sure of how predictably
>the auto works. Ideally I'd like to see a graph for the T32 with millisecs
>on the horizontal axis, and power on the vertical axis. Any way to get that
>info?
>
>BTW I do have a basic flash meter.
>
>Any advice here?
>
>BTW here is some excellent background info on shooting hummers:
>http://www.rpphoto.com/howto/hummer/humguide1.htm
>--
>Matt BenDaniel
>matt@xxxxxxxxxxxx
>http://starmatt.com
>
>
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>
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--
Matt BenDaniel
matt@xxxxxxxxxxxx
http://starmatt.com
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