Re: [photo-3d] Re: Medium format viewer

["Dr. George A. Themelis" <drt-3d@xxxxxxx>]

I remember when I got started in 3d with a Radex viewer
(inexpensive plastic lenses, 50mm FL or longer) and then
switched to the red button, I was disappointed with the
red button because some of my favorite slides did not
look good any more.  The higher magnification and
brighter illumination of the red button made all the problems
pop out.  But the BEST of the BEST, looked better
than ever.  

I think the "eyes" get used to using a certain viewer 
(lens) and tend to "dislike" it when a new viewer is used.
Especially if you use the new viewer to view images
which you had studied ("memorized") with the old viewer.

> Does a lens with a different focal length than the "normal"
> changes anything in the perceived depth of the stereo image???

YES.  If the viewing distance is greater than the recording
distance (I use distances or angles instead of Focal Length
of lenses, because the images could be freeviewed or viewed
with mirrors, etc., no lenses) then the depth appears increased.
If the viewing distance is shorter than the recording distance
then the depth appears compressed.  The names "stretch"
and "squash" are used for these situations.

You can convince yourself of these effects by doing a
very simple experiment.  View an anaglyph and then
pull it away, thus increasing the viewing distance.  The
depth appears to be increasing due to "stretch".

The effect is by no means proportional but it is there.

George Themelis