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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