1940 was an odd time for Zeiss to introduce an expensive luxury item to the public, but they did. The 35/4 Stereotar C
was designed to take two stereo pictures on a full frame 35mm slide. It is very similar to the 35/3.5 Stereotar C except that the lens does not have an arm that contains part of the rangefinder. I believe it can be used on any Contax camera. It was supplied with a prism to increase the stereo separation at distances over 2.4 meters, and a separate viewfinder.Known examples fall within a block of 500 numbers, and this is a very rare lens.