[MF3D.FORUM:1024] Re: Deviation, the stereo window, definitions

[Abram Klooswyk <abram.klooswyk@xxxxxx>]

David W. Kesner 1 Aug 2000:

>If I had two film chips where the separation between the near 
>points is 2.0mm when infinity is zero deviation and I then 
>mount so that infinity points are now separated by 2.0mm in 
>relation to the mount aperture spacing then the same near 
>points would be separated by 4.0mm.

>The point I am trying to make (and not doing so very well) is 
>that there is a point at which you can no longer comfortably 
>view an image because the "separation" between homologous 
>points is too great. 

I realize that petty remarks or splitting hairs on definition 
issues is a threat to the friendly atmosphere of this list, 
so I hope you forgive some additional comment :-). 

A separation of 2 mm makes no sense when we discuss normal 
stereopictures (would only occur on printed anaglyphs).
(On slides, separation is the distance between left and
right homologues)

Suppose a mask aperture separation of 62 mm, near point 
separation also 62 mm (mounted "to the window"), infinity 
separation 64 mm. Then near point deviation as well as mask 
aperture deviation is 2 mm (64 - 62). Are you saying that you 
move the chips 2 mm out? That would increase mask aperture 
deviation to 4 mm, but of course would not change deviations 
on film. When the difference in viewing convergence between 
looking at infinity and looking at the near point is two 
degrees, then looking at the stereo window plane would require 
an additional two degrees of convergence, after the shifting 
of the chips. The total convergence difference of 4 degrees 
could be hard to view. 

Is that what you are saying? Then I would generally agree,
taking in account that there would be no object between the
window and the near point.

However, 4 degrees can be acceptable with more gradual 
increase in depth. This is related to "double depth" 
mounting (Krause, Ferwerda).

Abram Klooswyk