P3D Re: Cardboarding

[Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Sat, 24 Jan 1998
>From: boris@xxxxxxxxxxxx (Boris Starosta)
>..............
>Now, I specifically remember a very lengthy series of Posts, this past
>summer, that seemed to conclude (with as much consensus as is possible on
>P3D - namely, not much) that one cannot in fact approach ortho imaging of a
>remote object by combining increased focal length with increased
>stereobase.  At that time, and still at present, I am exceedingly
>interested in this particular problem, as it relates to orthostereo.  Shall
>we now re-open the discussion on combating "squash" with stereobase?

*****  The discussion included the fact that increasing the stereo base does
in fact introduce other distortions. It involves changes in all 3 dimensions
so is not a full substitute for being in the right place with your cameras.
However, as in most things this involves a matter of degree. How much
increased stereo base is needed to combat a specific lack of parallax
situation? Just because other distortions are involved doesn't mean
stereobase adjustment isn't a useful tool when it's either the only method
or just a convenient method.

>
>For your consideration, I submit Ron Labbe's photo of Leah
>(http://www.studio3d.com/pages2/people.html), which he has stated (to me in
>a private communication) was taken with a telephoto (I can't recall the
>f.l., but it was quite a bit over 80mm).  On the website, cross-viewing,
>the depth looks exaggerated (stretch), which implies to me, given the use
>of a telephoto, that the stereobase was not normal (>>70mm).  
>Ron, feel
>free to jump in on this.  I've not seen the slide, nor have I met Leah in
>person, so I cannot fully judge the image, but on the web it looks very
>strange to me.  I propose this is an example of the use of a larger
>stereobase to compensate for a longer taking lens f.l.
>.................

*****  According to the web page, the picture was taken with 135mm lenses
and used SLR's positioned base to base. It's a good example that shows how
telephoto with a slightly exagerated base can be the equivalent of being
much closer to the subject. The effect of the image is as if one were very
close. I find the picture very pleasant and not exaggerated, considering the
vantage point it provides. As to stretch and squash, that depends on where I
position my eyes relative to the computer screen.



Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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