P3D Re: Slide Mounting Rotational Error Mis-Correction

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

Michael, I am making an important correction to your otherwise EXCELLENT
summary (my correction in brackets[]):

>"Any rotation (even a small one) will introduce a vertical displacement 
>when the [stereoscopic horizontal] displacement is projected in the vertical 
>direction... Vertical displacements cannot be fused by the eyes and cause 
>eyestrain... The more depth in a stereo pair, the more the horizontal 
>displacements and the more of a problem will be a specific rotation."

To clarify:  Depth is associated with a displacement in the horizontal 
direction.  This is what we have been calling "on-film-deviation" (remember 
the discussions on 1.2 mm maximum on film deviation? :-)) I call this
deviation "displacement in the horizontal direction".  So, assume that 
you have 1.2 mm on-film-deviation. This deviation is in the horizontal 
direction *only* (in an image correctly recorded and mounted).  Rotating 
the pair will make this 1.2 mm. project in the vertical direction.  
(example, a 5 degrees rotation will result in 0.1 mm in the vertical
direction).  Vertical displacements do not contribute to the stereoscopic 
effect.  They only add to eyestrain.

>My personal lesson: Shoot as straight as you can, but mount straight (even
>if horizon is off level), as attempts at correction introduce trouble.

Well, it depends... What bothers you the most?  The off-level picture 
or the rotational mounting error introduced by rotating the chips?

Again, if there is little depth in the picture then the rotation of
the chips will not result in significant vertical error.  But if your
name is "1.2 mm Deering" then.... :-)

>(Between the vignetting and the lack of a level, maybe I best put the
>Realist 3.5 in the closet for a while and seek out a Kodak...)

I only wish I had a Kodak to trade you.... (But I don't, because I 
don't think they are reliable and I do not buy them :-))

-- George Themelis


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End of PHOTO-3D Digest 2992
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