P3D Project Two: Electronically sych the cameras

[Tom Deering <tmd@xxxxxxxxxxx>]

A few weeks ago, I was a lurker on this list.  I was interested in stereo
photography, but never shot any of my own.  Based on things I read here, I
finally got up the courage to make some equipment and shoot stereo.  For
most of you, these projects wll be too simple.  But maybe these projects
will lure some other lurker out of the shadows to take their own first
stereo pictures.

Project Two:  Electronically synch the cameras. At first I thought I could
just push the buttons at the same time.  this worked okay for still
pictures, but not well at all for moving subjects.  Based on some things I
read on Photo-3D, I decided to link the two cameras electronically.

The cameras I chose were simple point and shoot Pantax cameras.  They had
auto everything, which I thought would be handy.  I assumed I could solder
the two shutter switches together and I'd be finished.  It turned out to be
much more complicated.

It turns out the shutter button on a modern auto-focus camera is actually
two switches: a focus lock switch that kicks in when the button is halfway
down, and the shutter switch which fires when the button is pushed all the
way.  While I as at it, I tied the self-timer switches together also.

This is a little more complicated than it sounds.  I had to attach six
wires to a camera that was not designed to accomodate the wires.  I had to
partially disassemble the camera so I could trace the double-sided circuit
board.  I found four accessible points to attach wires.  For the other two,
I had to carefully scrape the insulation away from the traces on the board,
and carefully solder to them.  I had to keep my wires away from the rubber
part of the switch button.  I used a piece of ribbon cable cannabalized
from a printer cable.

But it was not so easy.  Everything seemed to work while the cameras were
apart, but not when fully assembled.  They alternated back and forth,
firing on the left or right only.

I disassembled the cameras, adding diodes as suggested on this mailing
list.  Again the cameras worked perfectly while disassembled, but
alternated after I put them back together.  I finally figured it out.
Turns out the cameras worked fine as long as I shorted the switches with
screw drivers, but not if I used the rubber mounted buttons. I guess the
capacitance of my body was playing a part to make it work.  If I insulated
the screw drivers from my body, the cameras fire alternately as before.

So I disassembled the cameras again, and chose a different method of
connecting them.  Instead of electrically connecting the two cameras, I
used double pole switches.  This fires the cameras simultaneously, but
electrically isolates the cameras from each other.  The first way looks
more elegant, since there are no clunky looking extra switches.  But the
clunky switches work.

While I was at it, I drilled a small hole on the top of one of the cameras
so I could operate the lever that opens the cameras.  That way I could
change film without removing a camera from the twin bar.  I drilled the
hole in such a way that a straightened paper clip would push the lever from
above.

The focus, shutter and timer all fire in tandem now, but the two cameras
are slightly "off" when using the timer. I guess the timing circuits are
not tuned exactly the same, and probably shift lightly as the batteries
wear.  Works fine for the occasional self portrait, or when I put the
camera on a long pole for a high angle shot.

Cost: a little over a hundred dollars



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