P3D Why don't 4" prints work for Holmes cards? (was Re: P3D replies on orthostereo)

[Paul Talbot <ptww@xxxxxxxxx>]

Peter Abrahams wonders:

> why don't 4x6 enlargements work with Holmes cards, that are usually
> used with 3x5 shots?

The short answer is because they are too big.  ;)

The 4x6 enlargements obviously have to be at least 4" apart when
mounted for side-by-side stereo viewing--otherwise they overlap.
(The easy way to measure is left edge of left image to left edge
of right image.)  An object at the window will have the same
spacing as the print spacing, and objects at infinity will be
even farther apart.  Stereoscopes for Holmes format views expect
the infinity spacing to be closer to 3."  You would have to crop
an inch or so from the width of the prints to get them down to
manageable size for Holmes format.

There may be other technical reasons for not enlarging to more than
about 3", but I'm too new at stereo prints to have that part figured
out yet.  

Paul Talbot


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