P3D Re: Changing stereo base with mounting

["KENNETH LUKER" <KLUKER@xxxxxxxxxxxxxxxxxxxxxxx>]

Bob_Maxey wrote:
> once the camera takes the stereo pair, the true stereo base is set, and
> regardless of how much the slide mount or apertures are manipulated or
> changed, the stereo base is still the same. It is fixed.
>
> If I take a photograph in which I have a separation of say 5 inches, no
> amount of changing the separation or apertures of the mounts will alter
> that fact. By the above reasoning, I can shoot (To some extent) slide-bar
> stereo without regard to any specific stereo base, and fix / correct it in
> the mounting.
>
> Please, none of the usual "You are a bonehead" comments, just a good
> explanation of my reasoning...good or bad.

Good reasoning.  The base is determined by the lens axis separation
at the time the picture is taken.  However, the viewing scheme
(involving the mount, viewer/projector) can be manipulated to change
the relationship between the axes of the eyes during viewing. 
Ideally, when looking at the distant point, usually infinity, the
eyes' axes should be parallel to one another.

If the axes of the lenses in the viewer have the same separation as 
the infinity points on the film chips, then the rays entering the
eyes will be parallel, regardless of what stereo base was used (and
regardless, also, of the eye separation of the person looking). 
During projection, if the infinity points on screen are separated by
the same distance as the watcher's eyes, then the eyes' axes will be
parallel when looking at the infinity points.  

If the mounting has been fiddled with so that either the chips or
the openings are moved closer together or farther apart, the apparent
placement of the stereo window may be affected, but if the rays from
the infinity points into the eyes remain parallel, the viewing will
still be comfortable.  It's when those rays are non- parallel that
the eyes get torqued and things get painful or unviewable.

Ken Luker

_______________________________________________________________
Kenneth Luker
Marriott Library Systems and Technical Services
KLUKER@xxxxxxxxxxxxxxxx


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