P3D Re: "built in" windows

[CanterMike@xxxxxxx]

In digest 3573, Abram Klooswyk writes, in part:

<< 
  I don't know what is in the 'pdf' version article on the F40
 (like to get a copy too),
 >>

(Please add me to this list.  I think we all would like a copy, by now!)


 <<
 but one of the differences
 between 5P camera's, Belpasca's and Verascope 7P camera's
 is the "built-in" window.
 For 5P it is 7 feet, the Belplasca has about 10 feet and
 the Verascope none (which in fact is a window at infinity).
  >>


I've been seeing references to (different) camera's "built in" windows for as 
long as I've been taking stereo pictures.  But I've never seen a good 
explanation of how this effect is achieved, controlled or altered.  What 
changes within the camera's engineering achieve this variety of window 
distances?


Mike Canter