Concave Mirror Viewers

[bjay@xxxxxxxxxxxx]

Peter Abrams, following his comments on antique concave mirror viewers
for planar pictures, asked "Were there any stereo viewers that used
two focusing mirrors?"

Since he said "focusing", I assume he meant concave mirrors.  I've never
heard of one, but a stereo view can be viewed in three dimensions using
only ONE concave mirror.  The principle of the concave mirror stereo
viewer is described by Arthur W. Judge in his book "STEREOSCOPIC
PHOTOGRAPHY", Third Edition, Revised, 1950 (Chapman & Hall Ltd.) on
page 166.  He recommends a mirror of about 4 ft. focal length, having
a diameter of at least 1 ft.




Fortunately, the principle can be demonstrated with a smaller mirror of
shorter focal length.  The problem is finding a convex mirror that is
sufficiently free of distortion unless, you are an astronomer with a
good telescope mirror.  I have found at least one magnifying make-up
mirror that was good enough, but most are not.

A non-tech, cut-and-try method will do for trying to view a stereo image
this way.  Place the stereo card upside down a few inches from
the mirror, and of course with the image toward the mirror.  Back off
from the mirror to that range of distances where the mirror gives an
inverted image, and try to pick up the reflection of the card.
Experiment around with distances and if you're lucky and have a good
mirror surface, you may be able to get it.



You can also view a stereo card in three dimensions with an ordinary
double-convex reading glass.  Using a reading glass 3 3/8" in diameter,
with a focal length of about 7 1/2", I place the card upside down
and, standing about 60" from the card, I place the lens in the center,
Date: Sun, 3 Mar 1996 20:31:03 -0600
Errors-To: 3d-moderators
Reply-To: photo-3d@xxxxxxxxxxxxxxx
Originator: photo-3d@xxxxxxxxxxxxxxx
Sender: photo-3d@xxxxxxxxxxxxxxx
Precedence: bulk
From: photo-3d@xxxxxxxxxxxxxxx
To: Multiple recipients of list <photo-3d@xxxxxxxxxxxxxxx>
Subject: PHOTO-3D digest 1209
X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
X-Comment:   The Stereoscopic Image (Photo-3D) Mailing List  

between my eyes and the card.  After a little maneuvering, blinking and
head shaking, I see three contiguous frames, and the center one is 3D.

Incidentally, on page 260 of the above-mentioned book, Judge describes
the concave mirror for planar photographs.



------------------------------