P3D Re: Holograms and true 3D

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Fri, 22 Jan 1999 22:20:56 -0700
>From: Dale Walsh <dwalsh1@xxxxxxxxxxxxxxxx>
>Subject: P3D Holograms and true 3D

>...The way I understand it, from seeing many of them, is that a three
>dimensional light _object_ is recreated and sits in front of and/or
>behind the flat plate which (only) stores the necessary retrieval
>information.  It is possible to put your hand into this light object.

Worded like that, I don't agree. Two pieces of evidence:

1) If an opaque object is imaged, only the side facing the film has any
   relevance to the hologram. For example, a hologram of a pair of opaque
   dice does not contain anywhere within it the numbers that were facing
   away from the film when the hologram was made. A real *object*
   (light or otherwise) would have a back side.

2) If you make a reflection hologram of an object, and configure it
   (I think I've seen these) so that the image apears to be three
   inches behind the surface of the medium, and you then mount the
   hologram on a concrete wall, I don't think an actual light object
   forms three inches inside the concrete wall.

John B could probably word this better than I could, but I don't think he
reads P3D. You might want to move the discussion to T3D.

John R


------------------------------