P3D Re: PHOTO-3D digest 3743

[Olivier Cahen <o_cahen@xxxxxxxxxxxxxxxx>]

	In the two or three last issues of Photo3D, there was a discussion
about the stereo window and its location compared to that of the screen.
	I think that the window can be much better understood if you give a
proper definition of what the window actually is: it is a part of the
stereo image. It is the stereo image of the inner borders of the slide
mounts.
	Once the slides being fixed in their mounts, it is no more possible to
move the window versus the image by any adjustment of the projectors,
except if you can move a slide so that some lateral part of it goes out
of the field of the projector. I do not think that even the TDC
projector is able to do that.
	Some people claim that the window must be set to the screen, because
they sometimes see some confusion at the window if the left or right
borders of the image do not coincide on the screen. This is not correct,
the confusion that they see is only due to bad mounting, with the window
too far away, leading to floating edges.
	I fully disagree with David Kesner when he says
"I don't see a reason to not have it at the screen". Sorry.
	If the screen is large (more than 12 ft high) like it was in the last
ISU Congress in Germany, normal mounting (homologues at the infinite
being displaced by  1.5 mm for instance) would lead, if the window is
set at the screen, to a homologue displacement on the screen as large as
one hundred and fifty times this displacement on the film, i.e. up to
nine inches !
	Nobody, at least in the first ranks of the room, less than thirty feet
away from the screen, can have any pleasure in watching such a
projection.
	Olivier Cahen, France.