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.
Note: Jim has also kindly provided a series of pictures of his Rebel X twin rig.
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