Re: Keystoning

[T3D John Bercovitz <bercov@xxxxxxxxxxx>]

Sam Smith writes:

> OK, here's my first entry. I had a discussion with a fellow 3Der regarding
> toeing-in for stereo, or Keystoning. It obviously has problems with
> distortion in conventional stereo photography, especially in the corners.
> But what happens when there are no corners? Can you still get distortion
> with the circular subject? He was thinking of using extreme fisheye lenses
> in stereo, and wanted to toe them in. Would there still be a distortion?

Fisheye lenses cause distortion in 3 space as well as in 2 space but that's
another story.  Let's simplify and ameliorate the problem by looking at a 
rectilinear wide angle lens.  If you mean literally a circular subject, in 
other words a circle (no depth), the oblique views due to toe-in will give 
you ovoids (egg shapes) to look at.  When you try to merge one egg with the 
big end to the right and the other egg with the big end to the left, you'll 
get depth added.  The best place to learn about this is at Andrew Woods' web
page:
       http://info.curtin.edu.au/~iwoodsa/
See:
       http://info.curtin.edu.au/~iwoodsa/spie93pa.html

You can also pick up this same paper from bobcat:
       ftp://bobcat.etsu.edu/pub/photo/photo-3d/technical/
and get either: woods93.pdf (in acrobat)
or: woods93.ps.Z (in UNIX-compressed post script)

John B


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