close-up stereo separations

[P3D <koganlee@xxxxxxxxxxxxx>]

	There has been some discussion of formulas for determining camera 
separation for close-up stereographs, so I thought I would add my 2 cents. 
I'm sure that the formula based on magnification has a lot of merit, but in 
my opinion, even if it is theoretically accurate (and I have no reason to 
believe that it is not), it will not necessarily produce the most 
aesthetically pleasing image. I believe that my system is almost foolproof 
from a practical standpoint. It is based on making 4 exposures at varying 
camera separations and seeing which of 6 resulting separations works best. 
If you choose the starting point with care, you will easily have one or more 
separations which are obviously too deep and likewise those which are too 
shallow, leaving one or more in the middle which should be ideal. From 
experience I've found that for subjects which are individual objects (such 
as flowers), a separation of about 1/20 the distance from the lens to the 
subject works pretty well. From that I figure that twice that distance 
(1/10, that is), should surely be too much. For ease of understanding, let's 
say that the subject is 30 inches from the lens. Dividing 30 inches by 10 
gives a maximum separation of 3 inches (that should certainly be too much). 
Next divide the 3 inch separation by 6, resulting in .5 inch. That will be 
the minimum separation (and will almost certainly be too little). You will 
then make a series of 4 exposures starting at the "0" point, the second 
exposure will be .5 inch away from it, the third exposure will be 2 inches 
from the "0" point, and finally, the fourth exposure will be 3 inches from 
the "0" point. The series of 4 will look like this: 0 inch, .5 inch, 2 
inches, 3 inches. This will result in separations of .5, 1, 1.5, 2, 2.5, and 
3 inches. With a little practice in determining the "too wide" separation 
you should get perfect results using this method.
	If you have some sort of slide bar you should be able to use it for 
this purpose. Alternatively, you can purchase a close-up focusing rail from 
Porter's, Edmund Scientific, or one of a number of other places. This rail 
has a smoothly geared movement both forward and back, and side to side. It 
is well worth it if you like this sort of imagery. By the way, resist the 
impulse to "toe" the camera in to the middle. As someone else pointed out, 
it changes the shape of the image. Feel free to e-mail me directly, or to 
call (408-476-0702) if you have any questions about this.

					David Lee


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