Xref: utzoo rec.photo:2495 sci.electronics:2904
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From: strong@tc.fluke.COM (Norm Strong)
Newsgroups: rec.photo,sci.electronics
Subject: Re: Flash photography
Message-ID: <3632@fluke.COM>
Date: 3 May 88 17:48:54 GMT
References: <4840@bloom-beacon.MIT.EDU>
Sender: news@tc.fluke.COM
Organization: John Fluke Mfg. Co., Inc., Everett, WA
Lines: 36

In article <4840@bloom-beacon.MIT.EDU> mbmizen@athena.mit.edu (Mark B Mizen) writes:
}I am interested in triggering a flash at the end of a time
}exposure.  I will be using a camera with an electronic shutter
}(Nikon2020).  I would like to use a switch which will initially
}open the shutter when the switch is closed.  When the switch
}is opened following the exposure, I would like the shutter
}to remain open for a short period of time after this while the flash
}is triggered.  The camera shutter would then close.  If
}anyone could suggest a simple circuit for doing this I would be
}most appreciative.  Thanks.

I make the following assumptions:

	You are supplying a mechanically operated switch which will operate
the camera shutter electrically.  When the switch is closed the shutter opens;
when it opens, the shutter closes.

	The open circuit voltage across the switch is +6volts or less.

	There is no connection between the flash unit and the camera
electronics other than this switch.

Now, attach a 10k resistor from the base to emitter of a cheap NPN transistor.
Attach the flash contacts of the flash unit from collector to emitter.  Put a
.05 uf capacitor from the base to the hot side of the switch in question and
the emitter of the transistor to the common side.  

When you close the switch, nothing will happen (the capacitor will discharge
through the 10k resistor).  When you release the switch the voltage will rise,
turning on the transistor and setting off the flash, instantly.  This will
happen before the shutter even starts closing--unless you have the world's
slowest flash unit.

Good Luck
-- 

Norm   (strong@tc.fluke.com)