I am a big admirer of an instrument, called the Visual Survey Telebinocular, made by Keystone View Company from Meadville PA. This is a stereoscope with achromatic lenses. Read the information here and you will know why I like this instrument so much.

• The Difference is in the Lenses
• Model 46C
• Model 46B
• My First Visual Survey - Impressions

The Difference is in the Lenses

What makes this stereoscope so special are the lenses. A regular stereoscope has lenses in the shape of a wedge, made by cutting an simple lens in half. The thickness of a typical stereoscope lens is about 7mm. The Visual Survey's lenses are made by cutting an ACHROMATIC LENS in half. As a result the VS lenses are much larger (and heavier) than regular lenses. The thickness of the VS lens is about 21mm, or 3 times as thick as the regular lens.

Here is what I wrote in photo-3d about the lenses:

The best part are the lenses which are ACHROMATS.  The difference in
optical quality between this scope and the run-of-the-mill Keystone or
other stereoscopes is very obvious to me.  When I got mine I was thrilled
and went back and looked again through my entire stereo view collection. 
I noticed the lack of chromatic aberration and the increased sharpness
that made details far away clearly visible.  I then went ahead and sold
all my stereoscopes (including the famous Red Wing) to keep this one. 
I love it and would let mine go for anything!

Visual Survey Model 46C

There are a few variations of this instrument around. The most common is the model 46C pictured above. In addition to the achromatic lenses, the Visual Survey offers the following:

• Wide viewing area (to fit eye-glass wearers)
• Forehead Support
• Adjustable Height
• Illumination (via a Tubular frosted bulb found in every hardware store today - 25W recommended)
• Plus the usual focusing stereoscope function by moving the card holder back and forth.

Again, from my photo-3d posting:

This is one of the best (the best?) stereoscopes you can ever hope to use.
It is a table-top unit (not portable) with a heavy base, adjustable height,
forehead support, wide opening for glass wearers, etc.  It can be
transferred from a table to a storage place but it is best used on a
table with the user sitting in a chair and resting comfortably. 

By design this stereoscope is not very pretty, but who cares???  Because of
the large size and possible emotional attachment, spouse prior approval is
highly recommended. ;) ;) ;)

Visual Survey Model 46B

This is a more rare version of the VS Stereoscope and has a few extra features:

• Second light bulb between the lenses with an extra switch in the side
• Metal holders (perhaps to block one eyepiece at a time) next to the lenses
• Extra adjustment for the tilt of the headpiece
• Back mask flips open to reveal a wider mask
• Fancy stereo view holder graduated in diopters (focusing can also be locked between two extremes) & scale for measurement of convergence

		These close-ups show the extra bulb, head tilt adjustment and metal holder next to the eyepieces (the right holder is removed in the right picture)
		In my 46C I have removed the metal mask behind the lenses to be able to see more of the viewing area. In the 46B model the narrow mask swings open to reveal a winder mask underneath!
		The slide card holder is made out of metal (vs plastic for the 46C) and has two metal scales.
		One scale is graduated in diopters (to measure focusing) and the other in angles (?) to measure convergence or divergence.

My First Visual Survey - Impressions

I remember how I got my first Keystone Visual Survey stereoscope. A friend from photo-3d, M. S., offered to sell me this stereoscope for a little over $100. I accepted but felt that I was doing him a favor and wasting my money because I already had some very nice stereoscopes at home. Perhaps I could sell it and break even, I thought. The stereoscope arrived, I opened the box and took a look. "Ugly duck" was my first thought. I decided to give it a try. Grabbed a few stereo views and took a look.

Wait!!! Just a minute!!! What is going on here??? There is something in the quality of the image that I have not seen before. Are my eyes being fooled? I run into the basement and pulled out all my stereoscopes. I checked the same view with every stereoscope I owned, plus the Visual Survey. No, my eyes were not being fooled. The image through the VS looked better than anything else!!! No sign of chromatic aberration (I could see false colors in every other scope I tried). Sharper images. More details, especially at infinity. Easier to my eyes. I could be viewing for hours with no fatigue.

WOW! This baby is here to stay! I gave it a good TLC cleaning and have it in my basement ever since. Whenever I want to enjoy stereo views, this is the scope I use. Later, from discussions in photo-3d and input from Alan Lewis, I realized the secret behind the optical quality of this instrument: It has achromatic lenses! While every other scope has simple wedge lenses, this baby has achromatic lenses. I know from my slide viewer experience what difference achromatic lenses can make. The large size of the lenses and large FL makes this difference lens significant, but it is still there. And a trained eye can pick it up very easily.

The bottom line: I sold all my other stereoscopes and kept this one. I bought another (smaller) stereoscope with achromatic lenses from Alan Lewis. And now I actively search, buy and sell these Keystone Visual Survey Stereoscopes.

I welcome information on the construction, use, and history of these superb optical instruments!

George Themelis

Information updated: 02/00 - mailto:DrT-3d@att.net