AFAIK, there was a little
difference between Dvina's and Volkhov's optical systems. Volkhow employed a TV camera, while Dvina used... two pairs of eyes (occupators of the 'doghouse') probably supplemented by some simple optics (scopes, binoculars? - I wonder, in order to see a plane from 20 km away, one should need huge magnification... Hpasp, how was the real range of optical tracking in Dvina, assuming perfect weather conditions?)