>In a previous comment, I raised the question as to whether the so-called
> "ortho" condition was really all that important (no one has answered this
> yet).

So you really want an answer? I thought it was obvious.
:
It wasn't important to Underwood & Underwood or Keystone or apparently any of the makers of
stereoview cards. It didn't seem important to David White or anyone else using the Realist format.
They all used longer FL lenses in their viewers than in their cameras. It stretched the depth
resulting in more depth and liked it. They also, with a few exceptions, used a wider than eye
spacing base, which makes the objects in the view look smaller than they really were. To them
"ortho" was not important, maybe not wanted, and they made a living selling 3-D.

"Ortho" is making and viewing stereo pictures with an overall magnification of 1 (one). An "ortho"
view will look to be the same size and shape with the same depth as it appeared to the photographer
directly. An object will have the same angle of view in the viewer as it had directly from the
position where the view was taken. This is not "art"; it is copying a scene for viewing later. "Art"
requires some creative input.

"Ortho" requires a base that is eye spacing and a viewer with lens FL equal to the Camera lens FL.
Of course nothing is perfect so you can't get "Perfect Ortho". There will always be something that
is not exact. Lenses are not perfect nor are they perfectly matched. Of course not everyone has the
same eye spacing. Not a good reason to not approach a realistic looking view as best you can, if you
want.

Ortho is at a point between "Hyper and Hypo" and between depth "stretch" and "compression". It is a
point for the "Artist" to use to measure the degree of stretch or compression and hyper or hypo that
he puts into his artistic stereoview. A point that is nice to know. Can save time and film by
allowing him to calculate the amount of artistic distortion he will put in the view before he starts
shooting.

This is the MF 3-D list. Those here should be somewhat familiar with "ortho" as that is what most of
the MF stereo cameras/viewers do. Most have a base between 62mm and 65mm with FL generally in the
75mm to 80mm range and the viewers mostly have a FL in the 75mm to 80mm range. Those using these
cameras and viewers are already shooting "Ortho". I for one went from 35mm to MF to shoot
stereoviews that looked more real to me. Looking real is important to me.

Can MF be "not ortho"? Yes it can. One can extend the base using twin cameras or by moving a single
camera, and the FL can be changed on those and some of the stereo cameras. Has been done. It does
take some effort. Important to know what you are doing.

Can one make a wide-angle camera and still get "Ortho" viewing? Yes, use the wide-angle lenses on
the camera and put matching FL lenses in a viewer. That takes effort too but negates the "art"
factor and gets you back to reality only with wide-angle. Nice to know.

Is there a place for "non-ortho"? Yes. A good example is photographing fireworks. The attraction of
fireworks comes from its movement and colors. From the viewing positions it is generally a very
flat view, almost no depth at all. Not as good in "ortho" stills because the movement and color
changing are missing. An artist can, by adjusting the base and FL, add much artistic depth to the
view making it very attractive without the movement and color changes in progress. Important to know
how it works. It will not look like it did when you were there.

Chuck Holzner