A half inch shift produces almost no parallax and although the object is behind a window, the
depth of the object itself is so subtle most people won't notice.
A system of prisms and/or mirrors effectively places the object much further away optically than it is physically reulting in
very little parallax at a half inch shift. JPS version
One inch shift most people will notice the depth here, though it is still fairly subtle.
The optics of the scanner were designed to allow it to "see" the entire width of the scanner, but have the very useful side effects
of greater depth of field and a reasonable amount of parallax for a given shift, both of which come in handy for
stereoscopic scanning. JPS version