P3D Re: TDC Stereo Window Demo

[George Themelis <gthemelis@xxxxxxxxx>]

> Simply put a normal slide in, then while it's being
> projected, adjust the horizontal lens separation control of 
> the projector.
>
> This is suggested as a projectionist gag in the 1954 book
> "Three Dimensional Projection" by Earl Krause.  The gag is
> you can make something (like a cannon barrel) actively move 
> out from behind the window and come toward the audience by 
> doing this.
>
> Rick Inzero

Now it is time to clarify this:  There are three elements: 1)
Your subject (3d scene), 2) The stereo window formed by the
borders of the image (stereo mount), 3) The projection screen.

By adjusting the horizontal controls of the TDC (or any stereo
projector) you move your subject AND the stereo window with
respect to the screen.  So, you can make the cannon barrel move
towards the audience but you will not make it move with respect
to the stereo window.  The only way to move the scene with
respect to the window is to shift the chips with respect to the
mount.

Obviously some people are confusing the stereo window with the
projection screen since for most (small screens) the two
coincide (i.e. the projectionist adjusts the projector so the
stereo window is formed on the screen.)  But as we discussed
earlier, this is not the case in large screen projections.

The gag that Krause suggests (I'll have to read his book again
to see his exact wording) will work only if the stereo window
(formed by the mount) is not well defined.  For example, if you
project your image so it spils out of the screen, the boundaries
(and hence the window) are not clearly seen.  In this case, the
spectator normally sees the surface of the screen as the stereo
window.  By moving the projector horizontal adjustment you can
make it look like the cannon barrel is "moving out of the
window". 

George Themelis


=====
George Themelis, DrT-3d@xxxxxxx
http://home.att.net/~drt-3d/
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