Today's thrifty find was a 1950s Sterling "Inter-Ocular Slide Viewer", a handheld device for viewing stereoscopic slides -- either mass-produced sets, or (as came with this viewer) photos you shot yourself with a stereoscopic camera -- and works with two stereo frame styles, known as 5 Perf (American) and 7 Perf (European).
Imported into the U.S. from the Richard Verascope Company by the Chicago company, Busch Camera Company, branded under the name Sterling Stereo Viewer, the Sterling viewer embraces the design considered the most comfortable design for holding and use.
So I got the unit in grey marbled Bakelite, the original box, a box of 10 slides shot in the 1950s mostly of two boys, the warantee card which tells how to adjust the focus (rotating the eyepieces) and eyepiece distance to go between the frame types (the red switch), and the four-page manual (which I will scan for you in the near future).
The unit is internally lit with a flashlight bulb and two D-cells, with the light button being the red oval on the underside. (Notice there's also a tripod mount on the bottom!) Just pop a slide into the slot on the top, press the light button on the bottom, and peer in to see the images in three dimensions (or a reasonable facsimilie of 3D that a stereo camera was able to shoot).
Here's a picture of the inside, showing the battery chamber and the light, along with the long set-screw that holds the lid in place. I will scan the slides (rather, one image from each slide) also in the near future, though you will not be seeing them in amazing 3D. ;-)
A bit more history can be found on VintageViewers.com
