P3D Re: PHOTO-3D digest 2830

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

RE: Thanks to John R. for reminding me I forgot to edit the Subj. as
I usually do.
I have come to the conclusion that I described a true hologram and
that most of the "holograms" viewed without a laser are in the class
called psudo-holograms and can range from near true ones to
lenticular constructions. I understand the National Georgraphic
covers are pseudo-holograms as they can be viewed in normal light.
BobH

There are holograms which can be viewed in ordinary lighting which are
"True"  holograms with full parralax and even those that are viewed with a
laser can generaly also be viewed with other monochromatic light such as
sodium vapour like some yellow street lights. Those seen on  magazine
covers only need to lose vertical parrallax in a trade off as a result of
the technique used to make them visible in white light. Some of them also
have only stepped horizontal parralax having been made from a series of
photographic images panning the object or rotating it. This is done for
subjects that move either in order to record the movement as well or
because many such subjects will not be able to keep still enough for the
maximum of 1/10 wavelength movement required for a holographic exposure.
The only other way to do this to produce a hologram with full parrallax is
to use a powerfull and expensive ruby pulse laser to freeze the action.
 I came across a book which described how to make a hologram from a stereo
pair but this is in my local library not the works library so I can't check
till the weekend. What we do have in our works library is Lasers and
Holography Winston E cock which illustrates and example by Bendix research
lab done in 1966 of a stereo viewer. This is placed over either a plaster
model of a terrain or a stereo pair of it, the text with the photograph
suggests it is the actual model and viewers like this can be used as simple
stereo microscopes provided the lenses can be pushed close enough together.
The main text however suggests that it is a stereo pair of the model and
that is what it looks like in the photograph but the depth of focus is
insufficient to tell for shure. Anyway the viwer can look through the
holographic stereoscope to see the stereo image .
                                                   P.J.Homer



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