Double depth - definition

[T3D Bob Aldridge <bob.aldridge@xxxxxx>]

->I'll try a short explanation of my own.  If you have too much depth 
->in a scene, you can increase the separation of the chips until the 
->nearest object is behind the window.  This works fine (in my 
->experience) as long as you don't have your infinity homologues 
->significantly more widely separated than the lenses in your viewer.  
->(It is entirely possible to increase infinity separation.  The 
->lenses of viewers are supposed to be 65 mm apart but the windows of 
->the mask are on 62.2 mm centers so you can increase infinity 
->separation from the standard of 63.4 mm all the way up to 65 before 
->you force divergence of the eyes.)
-> 
->Another way to do the same thing is to leave the infinity homolgues 
->at the standard 63.4 mm on center but decrease the mask aperture 
->separation, by, say, 1.2 mm.  You can decrease aperture separation 
->by doing surgery on the mask or by cropping an equal amount from the 
->left side of the left aperture and the right side of the right 
->aperture.  This approach is called "double depth".

A very clear explanation. Do look it up in Ferwerda. The second method
is the best, in that if you keep the maximum infinity separation, then
you won't strain the audience's eyes with too much divergence IN
PROJECTION. Masking the slide as in the second method simply moves the
window off the screen towards the audience so that the whole scene is
behind the window. In a truly dark room, the audience will not be able
to detect the plane of the screen, so they'll just get the sensation of
having a window that is closer than the nominal 7 feet as laid down in
the "Realist system". This way, theoretically, it should be possible to
move the window so it's hanging VERY close in front of the viewer. I
guess you'd run out of chip area, before this became unviewable, but I
haven't tried it.

->Both of these methods will put the nearest object behind the window 
->when there is more depth than allowable under the existing rules 
->(62.2 & 63.4) in the scene.  However, in projection, the former 
->solution causes divergence and the latter solution lifts the stereo 
->window off the screen.

As I said above, lifting the window isn't, in itself, a problem in
projection, provided the room is truly dark. If it isn't, then it can
look strange to have a window hanging in front of a clearly seen screen.

My 50 cents' worth.

Bob Aldridge    Stereoscopic Society Projectionist


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