Stereo-Tach Stereo Photography Attachment (about 1939-1951)

The Stereo-Tach (rhymes with attach) is a gadget for taking stereo pictures with just about any camera from 35 mm to 4x5 large format. It uses four front surface mirrors to put two pictures with slightly different viewpoints side by side on the same negative. The stereo pairs are in portrait format. The stereo baseline is about 70 mm, which is roughly the same baseline on most stereo cameras. To compose the picture through the camera viewfinder you have to remember that the image is only half as wide as a normal image. The waist level viewfinder can be used to compose the picture if the Stereo-Tach blocks the camera's viewfinder.  You also need to double the exposure.

A Series VI insert is attached. The inner recess is for a

Series V insert. The outer recess is for a Series VII.

The Stereo-Tach in the pictures has a Series VI insert to attach the Stereo-Tach to an adapter ring for the camera lens. Series V, VI or VII inserts and adapter rings could be used for lenses ranging from 3/4" to 2" in diameter. When an adapter was not available for the lens an adjustable mounting bracket could be used to attach the Stereo-Tach to the tripod socket on the camera body. The Stereo-Tach needed to be level with the camera and centered on the lens to work.

A matching slide viewer was available. The images of a stereo pair appear slide-by-slide on a standard 35mm slide. The viewer uses four mirrors to reflect the images and get the separation needed. The viewer could fit inside a unit with a battery powered light for illumination. A print viewer was available.

Stereo-Tach ad from the July, 1939, issue
of Popular Mechanics, page 144A

The Stereo-Tach was invented by Charles D. Austin. It was first made by the Commonwealth Manufacturing Co., Cincinnati, Ohio, and later by Advertising Displays, Inc., Covington, Kentucky. The list price for a set containing the Stereo-Tach and the slide viewer was $22.50 plus tax in 1948. The price was cut to $17.70 about 1950. Sets were made for cameras using 35 mm film, roll film and Polaroid film. The Stereo-Tach could not fit some cameras like the Kodak Bantam Special where there wasn't enough clearance around the lens for the attachment. The Stereo-Tach stayed on the market only a few years. The beam-splitter principle used in the Stereo-Tach was used in stereo attachments from other manufacturers including Kodak, Leitz and Zeiss. Pentax made one in the '70s for 35 mm SLRs.

A stereo pair made with a Stereo-Tach

The mirrors in a stereo attachment have to be precisely aligned so the images are not tilted, which would spoil the stereo effect. The mirrors in this example are a little out of alignment. Being part of that roughly 4% of the population without stereo vision owing to strabismus, I'm not sure how bad this one is.