P3D Over-under twinning

[andy macha <amlor@xxxxxxxxx>]

In response to inquiry by The Searcher, I'll relate my recent experiences 
 in over-under twinning.

You can take stereo views in an over/under format or side by 
side format.  Which ever format you use will have to be viewed side by 
side, and either way makes a presentable image.  You will have to deal 
with the implications of the increased separation (another topic) but you 
may like having the option of shooting a scene in an upright or landscape 
format.

Over/under twinning can be done as simply as sawing off a 1/2 inch length 
of 3/8 inch bolt thread and bolting the two cameras together by their 
tripod sockets.  This presumes that the tripod sockets are directly under 
the center line of the lenses, and that when the cameras are bolted 
together, the lenses point in the same direction.  This was the case with 
my Minolta SRT's, and resulted in a 62 mm separation.  To take a picture, 
I would manually press both shutter buttons.

Conceivably, if the two cameras do not point in the same direction when 
tightened together in this fashion, one could place shims between the 
camera so that they do face the same direction when tightened.  Even if 
it does not tighten up, you could just grip both cameras with your hands 
and do your best, to align them.  I you are into mounting, you could deal 
with the inevitable small misalignments by trimming off the parts of the 
resulting image that are not shared in both film chips and mounting them 
in a smaller format.

I shot regular slides and viewed them in a Pinsharp stereo slide viewer. 
 There is also the Franka viewer and another viewer which accomodate two 
regular slides, all of which are featured in the Reel 3-D catalog 
(http://www.3d-web.com/reel/reel3d.html).

While the above described system is workable, I found that it was very 
easy for the cameras to become misaligned by rotating around the bolt 
that connected them.  Because of this, and the fact that it could not be 
mounted on a tripod, I progressed to another system.  Still working with 
the over/under concept, I constructed a base that each would solidly bolt 
onto each camera and then I bolted the bases together.  I was surprised 
that I still had to adjust this setup by placing cardboard shims on the 
edges of the bases to get the two cameras accurately aligned.  This 
increased the separation to about 82mm.

I managed to get some nice stereo views with this setup.  I also had 
another setup (A length of angle iron) to mount the cameras side by side, 
so had a choice of how I could compose the shot.  With the over/under 
setup, I found that I tended to take closer up shots.  With the side by 
side setup, I tended to take landscape shots.  One drawback of these 
systems is that if I wanted to shoot a scene in both formats, it took 
some time to break down one setup and mount the cameras in the other 
configuration.

One could overcome this drawback by connecting the cameras on a hinged 
base, as described in Ferwerda's "World of 3D" p. 115.  My experience 
suggests that this would have to be a very sturdy and precise hinge.  
Maybe someday I'll get around to doing this, or maybe somebody out there 
has experience with this.

I hope this info is helpful - Andy Macha


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End of PHOTO-3D Digest 2571
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