P3D Re: mounting to infinity (pt 1 of 2)

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Mon, 8 Dec 1997 20:34:40 -0700
>From: Larry Berlin <lberlin@xxxxxxxxx>

>>>>From: John W Roberts  writes:
>>>>(I would even venture so far as to speculate that to be truly "ortho",
>>>>a 3D photo should be mounted to *infinity* (if it contains objects that are
>>>>at "infinity"), rather than to *the stereo window*. I'm aware that mounting 
>>>>to infinity can cause serious problems for projection.)
>>
>>...I mean mount it so that objects which are at "infinity" in the photo
>>(e.g. the moon in the background of a landscape) also appear to be at infinity
>>(viewed with the eyes parallel) when seen in a viewer. 

>*****  This implies slides, not prints. 

No, prints can be mounted that way too.

>A hand held viewer seems to simulate the stereo window itself by placing the 
>viewer's eyes near the window and peering through. 

For a Red Button, etc., the apparent distance of the stereo window is set by
the geometric positioning of the apertures in the slide. Different mounts are
available for placing the window at different apparent distances. The viewer
itself does not create a specific stereo window.

>I feel that a properly mounted set
>of slides would look good in both the hand viewer and in projection. 

"Properly" is a judgement call. The topic of discussion, you will recall,
was "how to define 'ortho'", not "what makes a good stereo slide".

>The human eyes can locate and interpret
>infinity relative to the contents of the scene, so an absolute adherence to
>a fixed infinity separation seems almost pointless...

To you, perhaps, and usually to me, but some recent posts indicate that some
people have an extremely strong interest in making their 3D photos as much
like "real life" as possible. Relative (rather than absolute) reproduction
of depth may be a tolerable compromise for most 3D enthusiasts (because it
simplifies some other issues, as you note), but relative depth is not
the most "realworldlike" that can be managed.

My main point was that some people have been extreme advocates of
orthostereo as a way to reproduce "real life", but while concentrating
on focal lengths and interocular, they have generally been quite happy with
the usual practice of mounting the nearest object to the stereo window.
That approach produces realistic absolute depth only if the photographer was
careful (when composing the photo) to place the nearest object (tumbleweed
or whatever) at the actual distance from the camera matching the apparent
distance of the stereo window in the mounted photo. (No reason this can't
be done - it's just a little awkward sometimes.) To restate the above (and
possibly prevent further confusion): if you are one of those people who
want orthostereo, plus the closest possible reproduction of reality, plus
a stereo window, then you can accomplish all of these at the same time by
composing your photo (when you're taking the photo, as contrasted to when
you're mounting) so the nearest object is as far from your camera as the
apparent distance of the stereo window for your mounting method. If you
do anything different, then you will fail to meet one or more of the
qualifications listed above (though it still might be a fine photo).

To be continued...
John R


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