Kalart Automar projection lens. 50mm focal length, f/1.6. Coated optics. 2-5/8” long. Threaded barrel is 1-1/8” diameter. Front diameter is 1-1/2”. With a little creativity, this could make a nice 50mm eyepiece. Gives sharp wide field images when used with a copy lens or one of our objectives. Unused with front and rear lens caps.