P3D Re: Re: P3D Re: Re: P3D Re: Re: P3D Re: Re: A stupid (?) twin camera

[Jim Crowell <crowell@xxxxxxxxxxxxxxx>]

At 3:06 PM -0800 11/21/97, Michael Kersenbrock wrote:
>> Another way to say it is that the fields of view are only the same at that
>> one distance.  Imagine drawing two diverging lines in front of each lens
>> representing the left & right boundaries of the field of view.  These lines
>> will diverge more quickly for the shorter lens, and the two sets of lines
>> will only intersect at one distance...
>
>I think the original question asked was whether magnification correction
>by using different focal lengths would be useful to correct the inch or so
>difference in locations of the two cameras.  I think (hope) the answer is
>yes -- although 28mm vs 50mm is much too extreme.  It'd be more like 28mm
>vs 28.3mm or some such.  Perspective distortion by being an inch off won't
>be corrected, but some correction of image size may be correctable and
>useful.  Or so it seems.

...and the point John B. & I are making is that this is distance-dependent,
so that it's only possible to correct for this at a single distance for any
given set of offsets/focal lengths.

>If I tilt my face to the left and look toward the right, I'm putting my
>right eye closer to where I'm looking than where my left eye is.  But
>my eyes seem to still work okay even with the perspective difference
>distortion between the eyes.  So within limits, perspective distortion
>seems not to be fatal. :-)

I see what you mean; we were just talking optics, you're talking about
perceptual effects.  But the situation you describe is more analogous to
the uncorrected situation, in which the two lenses have the same focal
length (well, for most people; in some people the focal lengths of the two
eyes are noticeably different).

In the matched-lens situation, the fields of view of the two lenses are the
same at infinity and only diverge as you get close to the camera.  Changing
the focal length of one lens will make the fields match at some closer
distance but different at infinity.  It might be worth calculating how
close you have to get in the matched situation before the disparity becomes
appreciable...

-Jim C.

----------------------
Jim Crowell
Caltech Division of Biology
216-76
Pasadena, CA 91125
Tel: (818) 395-8337
Fax: (818) 795-2397
jim@xxxxxxxxxxxxxxx



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