[photo-3d] Re: twinning rebels

[JNorman805@xxxxxxx]

    I hope you'll forgive this rather long post, but I've been asked by a few 
people for details about my Canon Rebel twin rig.  In the belief that some of 
what I've done is equally applicable to other brands of SLRs, here's what 
I've been sending them individually:

    Here's how I've got my Rebel X rig set up:  The cameras are mounted 
vertically, so that their offset tripod sockets are directly opposite each 
other.  Each camera is attached to a bracket that I made out of half-inch 
thick wood.  The part of the wooden bar where the quarter-inch bolts go into 
the tripod sockets is cut out and covered on both sides with 1/16 inch 
aluminum, allowing access to the heads of the bolts with an offset wrench for 
camera removal and attachment.  The reason I mounted them vertically is to 
maintain a relatively small distance between the lenses -- in this case about 
75 mm center-to-center.

    In order to fire the cameras simultaneously, I bought two Canon remote 
shutter release cables, which are simple electrical cords that plug into the 
side of the body and are controlled by three-position buttons.  First 
position is off, halfway down activates the focusing and exposure metering, 
and all the way down fires the camera.  I snipped the button end off the two 
cords, making sure to leave enough wire attached to the button ends, and 
carefully spliced the camera ends of the cords into a single button.  The 
other button went into my junk box for future use on some other project.  
Pressing one button causes both cameras to meter, focus, and fire at the same 
time.

    I could have made life simpler by choosing to go with 50 mm prime lenses 
for both cameras, but I was intrigued by the flexibility of zoom lenses, 
running from 35 to 80 mm.  Problem was, how to link the zooms so that 
rotating the barrel of one also drives the other.  I found a 3/8 inch wide 
toothed industrial rubber belt in a junk shop on Canal Street in New York, 
and cut that into several lengths.  I turned it inside out, so the teeth were 
on the outside, and glued a piece around the circumference of the zoom ring 
on each lens.  Then, I found a couple of nylon idler wheels at the same junk 
shop.  The wheels ride on a ball-bearing hub, with a center hole of exactly 
1/4 inch.  I glued some of the same belting material around the circumference 
of each idler wheel, then positioned the wheels so that they were in contact 
with the belting on the lenses.  I attached the wheels to the wooden frame 
between the two cameras with a 1/4 inch bolts.  In theory, I figured, if I 
set both zooms at one extreme or the other, then turned one, the other would 
follow exactly along because of the meshing of my home-made "gears."  But the 
problem was that every once in a while the contraption would jump a tooth as 
a result of being knocked around (I'm a pretty physical photographer and tend 
to get into knocking around situations a lot), and the zooms would go out of 
synch.  I solved that problem by buying a piece of elastic fabric band from 
the local sewing store, and stretching it in a continuous band around both 
lens barrels so that the tension kept the lenses in constant contact with the 
idler wheels.  The elastic material is kind of lacey, and looks like it came 
off something you might find in a ladies' lingerie department, but at least 
it's black, and more to the point, it works!

    Next step: how to use flash with this setup?  The wooden bar that runs 
vertically between the two cameras has a wooden T-top epoxied across the top 
of it.  Imagine a letter T, with the two cameras mounted to the vertical.  I 
put a flash shoe on one side of the top surface of the T (not a hot shoe, 
just a bracket that I cannibalized off a cheap flash holder).  I put a 
Vivitar 283 into that shoe.  The Vivitar has a plug-out sensor unit in the 
middle of the front of it.  There's an available Vivitar "remote sensor cord" 
which fits into the hot shoe of either camera at one end, and into the the 
plug-out sensor receptacle in the flash head at the other end.  Most 
photographers use it for off-camera flash. You use it by unplugging the 
sensor unit from the flash and plugging it into the end of the cord that's 
mounted on the camera hot shoe, then the flash end of the cord plugs into the 
place where you took the sensor from.  

    Assuming the cameras are in proper operating order, and they meet factory 
specs relating to shutter firing, then pressing the single button will fire 
both cameras at the same time, and will also fire the flash that's hooked up 
to one of the two cameras.  Because the cameras fire at the same time, the 
flash exposure will be proper for both cameras. 

    For flash work, I set the cameras to the manual exposure mode, but leave 
autofocus on.  I decide what aperture I want (usually f 11) and set the flash 
to expose properly at that aperture for the speed of whatever film I'm using 
(usually 100 asa slide film or 200 asa print film).  I set the shutter speed 
to the proper synch speed or slower.  If memory serves, that's 1/90 sec in 
the Rebel line, but I don't remember because I ALWAYS choose a lower speed in 
other to get a little ambient room light to register on the film.  Generally, 
I find I'm shooting with flash at 1/15 or 1/30 sec shutter speed, sometimes 
slower.

    For ordinary outdoor non flash exposures, I set the cameras to aperture 
priority, usually at f 11, and let the cameras decide on the proper exposure.

    The only drawback to all of this is that it locks you into full-frame 
vertical format.  That's great for producing Holmes style side-by-side print 
view cards, but I haven't found anyone who makes a full frame vertical stereo 
slide mount.  As a result, if I want to project slides shot from this rig, I 
have to either use two synched carousel type projectors, or I have to 
jury-rig a spacer between the two mounted slides so they will fit into the 
rear channel of a TDC slide changer.

    One other thing: remember that T-top?  I glued an identical piece of wood 
across the bottom of the vertical bar.  When I'm shooting hand-held (almost 
always) that gives me something to hang onto, to help stabilize the whole 
setup.  I've also got a 1/4 inch T-nut embedded in the bottom, to serve as a 
tripod socket.

    That's about it.  If you have any questions, don't hesitate to ask.

Jim Norman