The twin lens Emitron camera used the long neck Emitron tube (EMI's Iconoscope class tube) and the second lens was for the optical viewfinder with inverted image. This restored example was photographed at the NMFPTV at Bradford. I have done some touching up of the picture to remove reflections and to make it nearer the original.
This camera was modified in the late 1940s to use miniature low noise valves in the head amplifier.