[photo-3d] Re: help ID an unusual old viewer?

[Bruce Springsteen <bsspringsteen@xxxxxxxxx>]

As has been said, Peter's description fits a Wheatstone pseudoscope (page
15 of Drouin), but the Wheatstone version was designed to view real scenes
directly in inverted depth, while the Dubosq viewer he noted (page 35 of
Drouin) uses the same principle in modified form to look at large prints
that are too big for conventional stereoscopes.  It seems likely that this
was the actual use of the scope Peter has (perhaps also for
transparencies, and in later versions with x-rays as Abram noted).

To use the Dubosq scope for a normal view (text reading left to right) of
the stereo scene, each image would have to be printed flipped, as in the
original Wheatstone mirrored stereoscopes.  Drouin describes the
usefulness of Wheatstone scopes in viewing large reversed prints,
transparencies, and drawings of symmetrical objects seen full face.  The
Dubosq viewer is describe immediately after this, in the same section,
which might be Drouin implying "here is a prismatic way to do what the
Wheatstone viewer does."  The adjustable aspect of Peter's item would seem
to support that use, allowing for a variety of print sizes.  Can't imagine
what else this viewer would be for.

As Drouin was originally published in 1894, this would allowably date
Peter's mystery viewer in the 19th century.  No inconsistency there.

Speculating,
Bruce

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