Giuseppe and Maria Fidecaro inside the spark chamber apparatus in the South Hall of PS to search for the $\rho \rightarrow \pi\gamma$ decay

The lens, the so-called front view (see album https://cds.cern.ch/record/1974123), was used in the S30 experiment to converge onto a camera parallel light rays from the front of a large spark chamber. A second identical lens, the so-called top view, and a large mirror were used to take pictures at 90 degrees in such a way to determine the x,y coordinates in the horizontal plane of each spark. Details of the optics are reported in the note: A $\gamma$-ray detector for the study of the electromagnetic decay of resonances, INFN/AE - 67/7, 20 Jun 1967, by F. Bradamante, G. Fidecaro, M. Fidecaro, M. Giorgi, F. Sauli, P. Schiavon.