The outstanding features of this Keystone Telebinocular stereoscope system are
1. high quality achromatic lenses
2. twin "lightboxes" which have two switchable 5-Watt light bulbs for viewing of stereo slides, transparencies, pin-pricked stereographs, etc.
3. built-in twin masks (40mm x 40mm and 47mm x 62mm)
4. A motorized switchbox identified as "Model 53 Rotor Control," which provides a variety of lighting conditions, such as simultaneous or sequential flashing of the right-eye and left-eye stereo slide images at various rates.
I would like to obtain a copy of the manual or catalog of this stereoscope. Please email me if you can help. I believe that this all-metal instrument was manufactured in the early 1950s, but am not sure.
Note that the main front unit of this stereoscope containing the lenses is identified on a small red plate as "Model 46C Ophthalmic Telebinocular." However, it has all the special features of Keystone's Model 46B, so this is another mystery. The combination twin slide carrier and transparency lightbox is identified on its small red plate as "Model 48 Ortho-Trainer." The distance between the left-eye and right-eye lightboxes can be varied by a single knob to--I assume--either test or optimize interaxial distances or eye convergence angles when used with independent stereo slides.
For further information about features of the wonderful Keystone Telebinocular Stereoscope--the "Rolls Royce" of all stereoscopes--click here:
3D by DrT: Visual Survey Telebinocular