P3D Re: Slide Mounting Rigs

[fj834@xxxxxxxxxxxxxxxxxxxxx (Dr. George A. Themelis)]

>How would rotating both chips result in vertical misalignments?

Very simple.  Just imagine the extreme situation of 90 degrees
rotation.  The stereo pair has displacements in the horizontal
direction (it is these displacements that lead to the sense of
depth).  If you rotate the pairs by 90 degrees then the horizontal
displacements will become vertical replacements.  Vertical
displacements cannot be fused by the eyes and cause eyestrain.

Any rotation (even a small one) will introduce a vertical displacement
when the displacement is projected in the vertical direction.

Now, this excercise shows that in addition to the amount of rotation,
there is another factor that affects the results:

   Amount of depth:  The more depth in a stereo pair, the more
   the horizontal displacements and the more of a problem will be
   a specific rotation.  If the images are flat then rotation is
   not problem.  (Another argument for "flat 3d photography"? :-))

I have rotated chips to level the horizon in a picture that I liked
a lot but the tilted horizon disturbed me.  The picture is viewable
but a mounting-sensitive person (have we agree that different people
show different tolerances to mounting errors?) would sense it.  It is
a rotational mounting error.

-- George Themelis


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