I think you will find that the Canberra PR9 had a minimum of 3 F95’s, and, for a few years, 5. The 3 were N1, P1, & S1, (Nose 1, Port 1, & Starboard 1 – numbering from the front). The additional 2 were a vertically mounted pair, mounted in the forward camera bay of the aircraft (the bay usually occupied by the PFO (Port Facing Oblique camera). These F95’s were used for ‘shipping’ sorties. One of the oddities was that the S1 camera was mounted upside down; otherwise the shutter blind worked against the forward motion of the aircraft, and gave rubbish results. In the PR9s, the only lenses that were normally fitted were 4 inch or 12 inch (the exception for a short time was a single F95 with a 3 inch lens, mounted vertically in the forward camera bay. This was used as a tracking camera for the larger 9 inch film format cameras)