P3D Bruce's Challenge - I

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

Bruce Springsteen ("our own") has presented us with many challenges.
I've taken up on his challenge to demonstrate the effects of changing
the main camera (recording) variables on the stereoscopic image.

But, first, which are these variables?  They are:

- F: Focal length of recording lens(es)
- B: Stereo base (distance of lenses of the camera system)
- I: Distance of the subject from the camera

(Note: I have conveniently selected the letters to spell FBI :-))

These three variables impact three metric (measurable with a ruler)
aspects of the resulting stereo image:

- s: Size of an object in the picture
- s1/s2: Relative size of objects, also known as "perspective", or
  "photographic" or "linear" or "geometric perspective"
- d: Stereoscopic deviations (this is the only aspect of the recorded
  image that is unique to stereo photography - i.e. you need a stereo
  pair to measure it)

Here is how this works:

- F: affects only s (F acts as a magnification factor, the larger the
  focal length of the camera the larger the size of the recorded 
  image).  As Brian Reynolds pointed out clearly some time back,
  the focal length does not change the perspective!  Only the distance
  does.

- B: affects only d.  That's unique to 3d.

- I: affects all three aspects.  By coming closer to the subject
  (reduce I), we increase the size of objects, intensify the perspective
  (increase the differences in size between near-by and far-away
  objects) and increase the stereoscopic deviations ("depth" is more
  pronounced in the foreground).  That's a good argument for coming
  close!!!

It is interesting to note that a traditional stereo camera has fixed
lenses (F and B) and the only way to affect the recorded image is by
changing the distance I.  However, this distance affects all aspects
of the image.

Going beyond the stereo camera involves experimenting with F and B.
And this was Bruce's challenge:  Show how these two variables affect
the stereo image.

To be continued.....

George Themelis