The most oddball 35mm SLR ever, the Contax AX, introduced in 1996, made headlines at the time with its unique ability to autofocus with manual-focus lenses. The AX used the Contax/Yashica lens mount (it is fitted here with a Yashica 50mm f1.9 lens), but the autofocus worked equally well with any make or type of lens that, where necessary via an adapter, could be fitted to it.

This was achieved by moving the film plane (together with the film chamber, mirror, focusing screen, prism - the lot), varying the distance from lens to film. When closed, the camera back did not move; the film was kept in contact with the gate by a complex, scissor-type pressure plate with the necessary 10mm of movement. With lenses of all but very long focal lengths it provided true macro-capability, even with the lenses set to infinity. Setting them to their minimum manual focusing distance allowed even closer focusing.

This “Automatic Back Focusing” mechanism accounted for the unusually deep camera body needed to house it.

It is shown, below, for size comparison, with two other full-frame 35mm cameras - the Olympus OM1 and (non-reflex) Minox 35EL.

It was, however, an evolutionary dead-end, because focusing was slower and less reliable than that provided by less-complex SLRs with autofocus lenses, and the AX was axed in 1999, superseded by the Contax N1.