T3D Re: Diodes in joined cable releases

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Thu, 28 May 1998 20:12:35 -0600
>From: Bob Wier <wier@xxxxxxxxxxxxxxxxx>
>Subject: T3D Re: Diodes in joined cable releases

>The second consideration is the way the circuit function - does it send a positve
>going pulse to trigger - or possibly a negative pulse? Or alternately does it *normally*
>have a voltage present, and does it fire the shutter by interrupting the voltage (I'd be
>surprised if so, because of the battery drain problem).

That's how the Minolta X-700 works (and I suspect most other cameras as well -
that way the electrical cable release can be a simple SPST normally open
switch). The X-700 uses a single conductor for its electrical cable release -
the outer threaded portion is electrically tied to the camera body (and the
tripod mount - I just use the metal camera bar (to which the two cameras
are mounted) as the return path. When the camera is turned on, a positive
voltage appears on the center conductor of the cable release (relative to
body ground). If the center conductor is shorted to ground, the shutter is
triggered. If the shutter is triggered by pressing the shutter button, the
voltage on the center conductor of the cable release goes to ground a few
hundred milliseconds later. When two cameras are tied together, pressing
the shutter button on one will also cause the other to take a photo, but
after a perceptible time lag. To get good synchronization, an external
switch is needed.

John R


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