T3D Single Lens Stereoscope?

[Peter Homer <P.J.Homer@xxxxxxxxxxxxx>]

The latest edition of the UK stereoscopic society bulletin describes a show
and tell session at the Mary Ward centre. David Burder demonstrated that an
antique stereo print could be viewed in stereo with a single large
magnifying glass held at waist hight with the print upside-down on the
ground. I tried this myself and it works although the image was not that
sharp with the lenses I tried. At this distance you are viewing an inverted
real image rather than the usual virtual uninverted one. Much the same way
as viewing distant objects with a magnifying glass. As with free viewing or
with a long viewing distance stereoscope without a septum there are three
images with just the middle one stereo, perhaps that could cured by a
septum. Also with higher magnifications the outer images can be lost over
the edges of the lens , but the best example I found was quite a thin lens
which gave a single large virtual uninverted image but which is actualy
pseudoscopic.
 I cannot understand how this works I can see that with the real image the
rays cross over causing the inversion and that as they diverge again beyond
the cross over  point they are directed to individual eyes ,but then I
would expect the image to be pseudoscopic whereas it is the other way
around. Is it because the individual images of the pair are reversed as
well as transposed?.
  The effect is somewhat similar to the stereomonoscope of Dubsocque (or is
it Duboscque) and the real image stereoscope of James Clerk Maxwell but
they still had a pair of lenses (and a ground glass screen in the case of
Duboscue) before the single large lens.  P.J.Homer





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End of TECH-3D Digest 304
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