P3D Re Stereo Window Demo, Krause's trick

[abram klooswyk <abram.klooswyk@xxxxxx>]

Larry Berlin forwarded a note by Rick Inzero (p3D 3742):
> 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.

George Themelis answered:
>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. 

Bruce Springsteen (P3d 3744): (...)
>The mind simplifies what it is seeing and says the scene "moved 
>away" or "came closer", but it is really more complicated than that.  
>This is what people are really seeing in Krause's (Freudian) cannon 
>gag.

Now before Krause becomes the victim of a Freudian
mystification :-)
let's read what Krause actually wrote:

>>It is possible to accentuate the window effect with a second 
projector to give a smash finale to the show. A single-lens 
slide projector can throw an unpolarized image of a picture 
frame with a completely black picture area in which the stereo 
projector shows a three-dimensional object, preferably against 
a black background. Then an effective trick is to turn the 
horizontal adjustment knob slowly and smoothly to make the
stereo 
object pass in or out of the picture frame. This is a
specialized 
trick calling for careful study of relative image sizes. It may 
not be desirable with any large number of general scenes
because 
exact coincidence of the non-stereo frame and the stereo window 
would be difficult to achieve. The projected border does hold 
attention and improve the continuity for a short period by 
eliminating complete screen blackouts when changing slides. 
If the projected non-stereo border can he put in motion as 
with a motorized kaleidoscopic projector or special effects 
machine, the plane of the screen is accentuated in comparison
to 
the depths in the stereo picture in the middle. These effects
can 
spill off the screen onto the wall or curtains as long as they 
mesh well with the 3-D images. <<
(Earl E. Krause "Three-Dimensional Projection" New York 1954,
p.56)

So there is no Freudian object mentioned. George is right in 
saying that the window _of the 3D scene_ is not defined (the
black background), but the trick was to create a 2D, but 
_binocular_ window around it.
Special effects with movements extending to wall and ceiling
were used in a show at the last ISU Congress in Lindau,
Germany.

On the effect of changing convergence: a quick but small change
can have a paradoxical effect: the convergence change is
percepted
as movement, but at the end the scene appeares _unchanged_ if
the screen separation isn't changed much (say 10 cm).

Abram Klooswyk