Re: [photo-3d] Digest Number 157, message 11

[Olivier Cahen <o_cahen@xxxxxxxxxxxxxxxx>]

	Hello Abram. I do not believe that the upper limit of the number of
depth steps is so small, as well in projected images as in lenticular
prints.
	I tried to read the book written by Prof. Okoshi. It contains too many
equations, and too difficult for me. He was a specialist of holograms,
and the book is entirely written as a theory of holograms. As far as I
remember, he started from the assumption that the resolution is defined
from the number of points that can be separated. This assumption is not
true in normal stereoscopy, since normal the depth resolution is about
60 to 80 microradians instead of the resolution of each view which is
about 300 microradians. This is at least one reason for which I cannot
believe to the results claimed by Okoshi. I often watched lenticular
prints, and I always found more than 30 depth steps, even in prints made
in conditions very far from the optimum defined by Okoshi.
	I do not understand how you found a number of depth steps would be as
small as 40 in stereo projection. Of course it depends where you are
seated in the room. When I was taught that the stereo resolution was as
sharp as 10'', I tried by showing to all members of my family a wood bar
with two lines of nails, so one could tell which of them was on each
line. All had an experimental resolution better than 80 microradians
(16''). I presented the stereo slides of this bar at a technical session
of the French Stereo-Club, and it was confirmed that almost all viewers 
had a resolution (in projection) better than 150 microradians (30'').
The resolution of the image on the film is not an important parameter of
the final depth resolution, since the results were almost the same on
images that I took so that it was fuzzy on the film.
	With a maximum depth, in figures of angular deviation, is known to be
about two degrees (7200'' or close to 30 milliradians) the number of
depth steps
in stereo slide projection should be at least 100 for most viewers. I
personnally think that is is even more.