disparity of image sizes

[P3D George Snowdon <gsnowdon@xxxxxxxxx>]

        I have just received the two Freeviewer's Assistants
from Alan Lewis.   The wood (fully assembled) model is
beautifully designed and made and, because there are no
lenses, the viewing is clear and free of distortion.
Stereographs of the Boer War  -  the first things
that came to hand  -  look even clearer than on the Holmes
stereoscope for which they were designed. 
        One thing puzzles me.   Because mirrors are used over 
the right eye, the photo-to-eye distance for that eye is about an
inch more than the photo-to-eye distance for the left eye.
Therefore, because the right-eye photo seems further away,
the size of the image on the right retina is smaller than
the one on the left.
        Why can I combine these two images of _different scales_
and, with no effort or strain, see a three-dimensional scene?
        Incidentally, the 3D view seems to be the same size
as the right-eye (smaller)image.
        [Thanks for the viewers, Alan!]

George Snowdon   


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