[photo-3d] Re: Red Button Anxiety, divergence

[Abram Klooswyk <abram.klooswyk@xxxxxx>]

To Jim Benbow's remark (05 Sep 2000):  
> In my experience small children may have problems with the SV1 
>because their  inter ocular distance is too small and that 
>viewer isn't adjustable.
George A. Themelis answered (5 Sep 2000):
>I hate to break the bad news but the interocular adjustment 
>will not help if the slide is mounted properly (with standard
>infinity separation.)  They can reduce the spacing of the lenses 
>but they will not be able to fuse the two images.

George just avoided (on purpose, I suppose :-)) to say that
the
opinion "viewer isn't adjustable" (to small interocular
distance)
is an old error.

Its traces go back to David Brewster, the correct optical
facts
were know since Hermann von Helmholtz (also way back in 
the 19th century). 

In "The World of 3-D"  by Jac. G. Ferwerda the issue is
explained.
(http://www.stereoscopy.com/3D-books/)

A scheme of the erroneous and the right adjustment is on the
web at: http://users.ticnet.com/view-master/vviewer.htm

In short, when children would adjust a viewer to their (say) 
55 mm interocular in viewing slides with 63 mm infinity 
separation, a considerable  _divergence_ of the eyes would be 
necessary for fusion, so: no fusion. 

(The only good thing about it is that they maybe could learn 
early to freeview old stereoviews :-).) 

Abram Klooswyk