P3D Re: Stereo Graphic's "Depth Master", Re Differential Focus

[abram klooswyk <abram.klooswyk@xxxxxx>]

Different focusing of lenses with equal focal length 
gives different image size on film.

As Bob Aldridge has indicated, the Wray Stereo Graphic trick is 
to use lenses of (slightly) _unequal_ focal length and position 
them at _equal_ distances from the film, so you get equal image 
size, but unequal focused distance.

A part of the depth of field of both lenses will overlap,
but at the far as well as at the near end of the overlap 
zone one of the lenses will give some blur.

Obviously you can get away with this, but it has been 
documented that introducing blur in one eye deteriorates
stereoscopic vision. I don't have the data on hand, it
might be true only for considerable blur, I will try to
find data if it interests anyone.

Abram Klooswyk


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