1mm ring and bayonet rear lens cap from 1960s – 70s
Toronto. After recovering from WW2, Leitz embarked on their famous M series bayonet mount cameras with the extremely popular M3 camera. Like many leading manufacturers, Leitz was aware of their strong base of owners of the older screw mount cameras. They tackled the transition from screw to bayonet mount lenses and cameras in many ways.
The last screw mount camera model, the IIIg was sold alongside the M3 and introduced a few of the M3’s features. Buyers of a Leica could buy either the M series or the IIIg.
While the screw mount Leicas were slimmer than the slightly larger M series cameras, the film plane to lens mount distance was actually one mm longer. The 28.8mm screw mount distance became 27.8mm in the M series. This allowed a 1mm thick ring to be added to an M series camera lens mount, converting it for use with older screw mount lenses. This meant owners with screw mount lenses could use them on the newer M series cameras.
You may have noticed that the earlier M series black Bakelite rear lens caps have three odd tabs moulded on their outer back. Did you ever wonder why? They were actually a three tab wrench! Occasionally the 1mm ring converting bayonet to screw mount got stuck on the camera. This ‘wrench’ could make fast work of removing the ring. Of course, if the ring was stuck to the lens, a cloth between hand and ring made short work of freeing it up.
Also, most rings are marked with a lens focal length. The ring would lock in the correct bright line in the viewfinder of the M series camera corresponding to the chosen lens! Anyone not that fussy could use any of this line of rings to convert a screw mount lens (and some lens accessories) to bayonet mount Leicas.
