T3D Re: orthoscopic afocal perspectives

[Tom Hubin <thubin@xxxxxxxxx>]

John Toeppen wrote:
> 
> Two lenses separated by the sum of their focal lengths will produce an
> afocal image relay.  Keystone distortion in stereo will still exist
> unless you translate the camera without changing its pointing(slide on a
> bar).  

With an afocal optical system, any single plane can be imaged on film
without keystoning. In theory it does not matter how you point the
camera. What matters is that the film or image plane be chosen properly.
Choose any 3 points in the object plane that are not in a straight line.
In other words, enough points to define a plane in object space. Point
your optics however you wish. Then determine where these 3 points are
imaged. This defines the plane where the film is to be. However oddly
positioned it may seem to be.

Translating without changing pointing angle is only necessary if you
will not or cannot place the film in the image plane that corresponds to
the object plane. This is one of the limits with a standard camera. As I
questionably understand phantagrams, a standard camera arrangement is
unlikely.

Tom Hubin
thubin@xxxxxxxxx
AO Systems Design


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