Converging lenses (was: Window reversal)

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Greg Wageman writes:

>converging (the lenses) introduces
>keystone distortion and isn't recommended, so window@xxxxxxxx would
>be the usual case, at least for educated stereographers. :-)

There are situtions in which positioning the stereo window
by convergence is more important than possible errors
introduced by keystone distortion.

Also, in single SLR stereos, to maintain alignment, it is
recommended that an object is marked (mentally) at the center
of the viewfinder and maintained there.  This practice will
also converge the lens to this object which might not
be at infinity.  Convenience is sometimes more important
than minor errors introduced by these distortions.

I was reading an article in the newsletter of the "In Depth"
stereo club of NJ, in which the author argued passionately
the merits of converging the lenses.  He sounded quite
educated to me.

If there are stereo photographers who, for one reason
or another, converge their lenses are are happy with what they
get, I'd say it is an acceptable practice.

-- George Themelis


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