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[OM] OM 10 and OM 20 TTL Flash???

Subject: [OM] OM 10 and OM 20 TTL Flash???
From: Jan Steinman <jans@xxxxxxxxxxx>
Date: Tue, 13 Oct 1998 11:27:22 -0700
>From: "Stuart Goggin" <SGOGGIN@xxxxxxxxxxxxx>
>
>...if I were to hook up a powerful flash
>to the OM10 or 20 body and have it trigger at exposure time,  shouldn't the
>body detect when the correct exposure has been made and shut the shutter.

Unfortunately, the shutter is a mechanical thing, and operates one to two
orders of magnitude slower than electrical things, like flashes.

The focal plane shutter requires 1/60th of a second to open, and another
1/60th of a second to close, but the flash dumps its full charge in
1/1000th of a second or less!

So the scenario is:
1) push the button.
2) 1/60th of a second later, the first curtain is fully open.
3) camera tells flash, "you can start now!"
4) somewhere short of 1/1000th of a second later, the camera tells the
flash, "alright, already! I've got enough light!"
5) the camera begins closing the second curtain.
6) the flash ignores the camera, and dumps it's full charge in the next
1/1000th of a second or less.
7) 1/60th of a second later, the second curtain is closed.

>...Maybe
>the second curtain release would not react fast enough to the flash exposure
>resulting in over exposure,   but it would be interesting to test out...

I'd think the best you'd be able to do would be less than 6% (1/1000
divided by 1/60) of the right side of the frame properly exposed.

My numbers might be off, but I think I they're in the ballpark. It ain't
gonna work!


: Jan Steinman <mailto:jans@xxxxxxxxxxx>
: 19280 Rydman Court, West Linn, OR 97068-1331 USA
: +1.503.635.3229

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