P3D Re: Super-hyper stereo: please help

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

DrT's Stereo Clinic To The Rescue:

>When attempting super-hyper stereo, should your camera pivot (pan) at all
>between exposures? 

It could... It's a free country.  Could you define "Super-hyper stereo"
for me?  "Super" and "Hyper" mean about the same thing only the first
is derived from Latin and the second from Greek.  I think simply
"hyperstereo" would do the job unless if you mean something really
special with this "super" like really long-base hyper.

>Certainly, when I use my sliding rail, the camera does not pivot
>and so I thought I should apply that same principle when
>branching out to a base of 30'. However, I quickly discovered that
>stretching the base that much *without* pivoting the camera even a little
>made it rather difficult to keep my subject (a tall building some 1000'
>away) in the frame. 

What focal length lens do you use?  This is more of a problem with
longer lenses.

>I realize that if I were to pivot the camera to the
>extent that a distant point on the horizon resided on the same point on the
>ground glass in both exposures, most of the stereo effect would be negated.

WHY???  No, it would not be negated.  (If you don't mind, please explain
why you think that the stereo effect would be negated...)  You will be 
introducing a small "keystone error" and, in exchange you could put the 
stereo window right at the point of convergence.

>However, perhaps there's a compromise to found somewhere. What is the
>accepted practice for super-hyper stereo?

>From a practical viewpoint, depends on how much image loss you are
prepared to accept.  Ideally, you should keep the lens axis parallel.
But if you lose quite a bit of image then you might want to converge
them.  You do not have to converge them to the closest object or
your main subject.  But if you converge to the closest object then
you will have the stereo window in the right spot and no image loss.
The penalty: Some vertical error due to keystoning.

My advice:  Experiment and see what works for you.

George Themelis


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