No Subject

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

>In reply to Bob Maxey's post my understanding of holography does suggest a
>similarity to lenticular images but the lenticles are microscopic . Being
>initialy produced by photographicaly recording the fringes produced by the
>interference of the object and reference beams  (Newtons rings). So that
>they could be as little as 1/2 the wavelength of the light used although
>there are few emulsions that could resolve this so the light is allowed to
>travel further and the fringes become larger but still well under the
>resolution of the human eye of 1/4 mm at about 20cm. When the plate is
>developed and fixed the removal of silver halide from the less fogged
>fringe areas causes them to shrink a little so a lenticular surface is
>produced in the emulsion .The first holograms depended on diffraction
>through the unfoggged areas but nowadays they are usualy bleached so the
>fogged areas also become more transparent and light is refracted through
>them. They do differ from lenticulars in that being produced from Newtons
>rings they are themselves overlapping ring shaped Fresnel lenses and there
>is parralax in all directions not just horizontaly and the number of views
>is virtualy infinite. The type of hologram most available to the public are
>the metalised plastic ones which have their parralax restricted to the
>horizontal more like lenticulars the advantage is that they can be viewed
>in more ordinary lighting . Some which are of animate objects whether
>actualy moving or not are also made up of a number of ordinary photographs
>of the object. So these have a finite number of horizontal views still more
>like lenticulars although still with far more views.
> I was given a mouse mat for Christmas which is holographic although more a
>holographic diffraction pattern with some depth and movement rather than an
>actual image . Unfortuneately the central area has already been worn away
>by the action of the mouse on the matt because the lenticles are so small
>this would not happen with a lenticular but I suppose it could eventualy
>become so worn that the image behind it was obscured.    P.J.Homer




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