My memory from 40+ year old Popular Photography coverage was a bit rusty: when I looked for verification today additional details of Leitz' Correfot experiments emerged. I only remember discussions of the SL2 prototypes back in the '70s, but evidently there were also versions based on the R3 and R4. There also seem to have been two flavors of AF detection: one based in the prism optics above the focus screen, the other mounted at the bottom of the mirror box like in modern cameras. Unconfirmed rumors suggest Nikon may have borrowed the prism-based system for their short-lived F3AF, the last prism-based AF detection design (also the only one to ever be make it out of prototype stage and get sold to ordinary photographers). The earlier SL2-AF prototype reportedly used an external minicomputer to process the signals from the detectors. The R4-AF here has the larger customized prism housing ala F3AF. These pics would also suggest an external AC power brick alternative to the huge MOT on-camera battery pack (which seems to have been demo'd most often with the original "manual focus aid" Correfot below, without lens).