T3D Re: TECH-3D digest 508

[JNorman805@xxxxxxx]

Dogbreath writes:

<< I would like to build my first twin rig from two 35mm SLR bodies. >>

There are plans and detailed instructions available for twinning Olympus XA-2 
cameras, including electronic linkage.  Obviously they are not SLRs, but 
people report good results.  Check the archives.

Personally, my primary rig is a pair of Canon Rebel X cameras (without the 
built in flash), mounted bottom to bottom.  Their auto exposure and auto 
focus functions are linked by way of two off-the-shelf shutter releases, 
wired into a single button from one of them.  Press the button halfway down, 
and the auto functions are activated.  Press it all the way down, and the 
shutters fire.  The shutters are simultaneous enough to stop birds in flight, 
flags waving in the wind, etc., with no retinal rivalry.  When I shoot with 
flash, using a Vivitar 283 or 285 attached by a remote sensor cord to the hot 
shoe of either camera, the shutters are simultaneous enough so that I get 
perfect flash coverage on both sides about 90 per cent of the time.  The rest 
of the time, I get a dark, underexposed band in the image produced by the 
camera that does not have the flash attached to it.  I can improve my odds by 
using slower shutter speeds and manual exposure and focus functions.  
	I use two Canon 35-80 zoom lenses (also off-the-shelf, with no 
attempt to test them for perfectly matching focal lengths, but they seem 
perfectly fine nonetheless).  The zoom barrels of the lenses are linked two 
ways:  first, by having cemented a band of rubber toothed industrial belting 
around each one and a matching piece of belting around a pair of nylon roller 
wheels that mesh with the zoom barrels so that when I turn one the other 
follows along; and second, keeping all the teeth of these pieces of belting 
in firm contact with each other by wrapping a piece of elastic material 
around both lenses.  Initially, I used a jumbo-sized rubber band that I was 
able to get from the Post Office, but when that wore out I was never able to 
find another like it, so now I use a piece of elastic ribbon that I bought 
from a local sewing store.  It's very lacy and looks like the stuff that 
Victoria's Secret buys by the mile, but at least it's black!  
	The two cameras are mounted in vertical orientation via their tripod 
sockets onto a 1/2-inch thick piece of wood.  The wood has a semicircular 
cutout for access to the 1/4x20 thread bolts that screw into the tripod 
sockets.  Both faces of the wood are sheathed by a piece of metal, 
approximately 3/64 inch thick (this is not critical; I used pieces that I cut 
from an old T-square).  The metal pieces are screwed into the wood, and the 
cameras are fastened to the metal pieces by way of the bolts.  The bolts are 
more or less captive in the bolt holes in the metal pieces as follows: the 
bolt holes in the metal pieces are drilled slightly undersize, and tapped 
with a 1/4x20 thread.  I clamped an electric drill in a vice and fastened a 
bolt longer than I would need in the chuck of the drill.  I turned the drill 
on and used a metal file to turn a groove into the shaft of the bolt just 
under the head (using plenty of 3-in-1 oil for cutting lubrication). I took 
the bolt out of my crude lathe, and threaded a matching nut onto the bolt, 
then used a hacksaw to cut the bolt to proper length, discarding the portion 
of the thread that had been deformed by the chuck of the drill.  Then I filed 
down the burr left by the hacksaw, and unthreaded the nut to make sure the 
thread on the bolt was perfect.  Next, I threaded the bolt through the metal 
piece mounted to the wood until it rotated freely at the place where it was 
grooved.  I carry a combination wrench with me in my camera bag to tighten 
and loosen the tripod socket screws as necessary (to change batteries, for 
example).  There is no interference with the camera backs for film loading. 
	I have cemented thin strips of rubber to the faces of the metal 
pieces to create a non-skid interface between the camera bottoms and the 
frame.  This helps to keep everything aligned, so that the cameras are always 
pointed in the same direction and parallel.
	Refinements: I have attached another pice of wood across the top of 
the connecting bar, creating a "T".  The flash shoe (not a hot shoe, because 
the flash is connected to the camera hot shoe by way of the remote sensor 
cable) and shutter button are located on that bar.  I have attached a similar 
bar to the bottom of the vertical connecting bar.  I use by left hand to 
support the who contraption from this bottom bar, and my right hand to hold  
the top bar and activate the attached shutter button.  Also, I installed a 
tripod socket in the bottom bar (using a 1/4 x 20 "T-nut") but in truth I 
have never used the socket.  
	The interoccular distance of this rig is 3 5/8 inches, so true 
closeups are not possible.  I love the sharpness of the Canon optics, and I 
am very happy with the results.
	Hope this info is helpful.

	Jim Norman


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