Obviously made for aerial tracking - the internal prism moves as the missile climbs resulting in less neck strain for the observer. CTS (Cooke, Troughton and Simms) made this one but I also have the Barr &Stroud version - both from the early 1960's. Nice big bits of kit with stunning wide angle optics
Comparison of the CTS wide angle optics with the big Sard. Note the CTS reticle Aslo shown alongside a B+S bino - weight 8.6 kg;
Excellent gear, Niall. And the movable prism does the trick...
Ingenious really Zbig. ;)