I acquired a lens with this marking today. It is clearly a 135, but there is no indication of any prior mark where the "5" should be, and all the markings are engraved. Has anyone heard of lenses with the missing "5"?
It would be interesting to learn how lenses were engraved. Small series likely were engraved manually on a tuntable with a milling device coupled to a pantograph reading a stencil. So a letter or figure could have been missed. But how was it done one large scale?
Typos and missing characters in the engravings show up from time to time. Normally it seems to be just one unit here and there but there does appear to be a whole batch of 6x7 helicoid extension tubes that were engraved with HERICOID.
I have an Olympus 38mm f/1.9 A to-s (Yes, the U is missing from Auto). Same as yours, no signs of damage...just a missing letter.
