T3D Re: Diodes in joined cable releases

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Thu, 28 May 1998 22:28:15 -0600
>From: michaelk@xxxxxxxxxxx (Michael Kersenbrock)
>Subject: T3D Re: Diodes in joined cable releases

>> My setup works fine without diodes. However, if the film is advanced in
>> the cameras, either camera being turned off will cause the other one to
>> fire. My usual solution is to disconnect the circuit between the two cameras
>> when turning them on or off.

>That sort of thing is what diodes should fix.  

That's pretty much the only reason a person might want to use diodes.
The philosophical difference is that I don't regard it as a *problem* that
needs to be fixed, but as a matter of convenience. The diodes don't serve
any useful functional purpose at the instant of taking the photo. My
design decision was on whether I should add something that could
conceivably impair the photographic ability of the system, to increase
user convenience.

>Just put a diode in series
>with each one then connect the sides not connected to the camera together
>and to the switch.  If a diode is backwards then that camera won't fire, so
>turn it around (easier than trying to explain diode anode/cathodes and such).

Good explanation. :-)  If you happen to get diodes with a "+" to mark the
positive terminal, those terminals should probably be the ones connected
to the camera releases.

>Chances are, the diode drop won't hurt things, although one could use
>schottkey (or germanium for that matter) ones with lower drop.  But it's
>unlikely, I suspect, for that to matter.

>From all the reports I've heard, even with the diode drop, the voltage is
generally below the threshold and the cameras will fire with the diodes
in place. On the other hand, I've gotten the general impression over the
years that the people who use diodes are more likely to comment on problems
with getting very precise synchronization - there *could* be a correlation.
My advice would be that if a person uses diodes, and can never seem to get
the synchronization within 1/500 second or so, they should at least try
without the diodes, and see if that helps the synchronization. (If it does,
I'd appreciate hearing about it.)

John R


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