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Re: Museum Displays (i.e. Page Museum)



"C. Laibly" wrote:

>         On the subject of great displays, I really enjoyed the La Brea
> tarpits Page Museum in Los Angeles over Thanksgiving break. They have
> a really neat saber tooth tiger holographic display. The image consists
> of two overlays that slowly fade in and out of the same space.
>  One image shows the skeletal structure while the other is the
> "filled out" image of the cat. I particularly enjoyed this as it provided
> an not often seen view of muscle/skeletal relationships.

Yes, this is just the sort of innovative approach I like to see, although it
is no replacement for viewing reconstructions and restorations in the round.
There is also a young woman's skeleton (the "La Brea Woman") which dissolves
to show the restored woman at the Page Museum.  Actually, this trick is
accomplished not with holograms but the simple use of a two way mirror set at
a 45 degree angle to the viewer.  One of the figures is viewed directly
through the angled glass or partially silvered mirror ("transmission"); the
other is usually around the corner inside the booth (that is, at a 90 degree
angle to the viewer's line of sight), and is seen as a reflection off the
angled pane ("reflection").  The lighting on each of the two subjects is
carefully controlled with rheostats so that as one figure becomes dim, the
other becomes bright, and vice versa.  The figures must be enclosed inside a
booth to disguise the optical trickery, and to avoid unwanted reflections
which would ruin the effect.

The angled glass or two way mirror is referred to as a "beam splitter."  The
semi-silvered side of the beam splitter should face the viewer.  The basis
for this trick dates back at least to some of the earliest trick photography,
if not to much earlier live magic acts.  It is the visual equivalent to a
motion picture "dissolve," although it is accomplished by different means.
Depending on the subject and the spatial logistics, the reflected model may
be above, below, to the right, or to the left of the view transmitted through
the glass.  Optics being what they are, the effect works in 3 dimensions, and
is unaffected by the viewer being tall or short or shifting about, although
suspicious visitors can detect the technique by looking into the exhibit at
extremely oblique angles (and viewing the model which is reflected).

There!  You can have your skeleton and a restoration, besides.

--
Ralph W. Miller III  <gbabcock@best.com>

And make that a sabertoothed "cat," as it is neither striped nor is it any
more closely related to tigers than to other members of the cat family.