retro... a Foth (Derby) Anastigmat 50mm f3.5 (c1934) uncoated lens originally fitted to a Foth Derby, taking 30x40mm negs on 127 film.
A mid priced camera, the Derby sold in several versions throughout the 1930s. It's not a particularly rare camera, the f3.5 lenses are perhaps twice as common as the f2.5. I've seen an f2.8 as well, but only once.
There is no indication as to which company made the lenses (Foth?), some have serial numbers, others do not. Some are Imperial ft & inches and others metric. The helicoid style though unusual is similar to some Zeiss lenses of the period.
Unfortunatly, mounted on a full frame SLR the helicoid fouls the mirror for anything over 3ft.. so here it is on M43.
A custom mount to something like M39 is relatively easy to engineer, except the flange depth can vary between cameras by several mm... so each adapter must be made to length to suit the helicoid of the lens.
As ever, no camera was harmed in the making of this adapter... it can be reunited with it's lens with the aid of a small screwdriver.