M to L39 adapter?

[dovevadar]

we have seen countless versions of L39 to M adapter... but just curious if anyone came across the reverse? It will be interesting to use a modern M lens on a Zorki...

[oscroft]

we have seen countless versions of L39 to M adapter... but just curious if anyone came across the reverse? It will be interesting to use a modern M lens on a Zorki...
It's not possible - or at least, not without an adapter with extra optics in it.

The reason is that an M-mount lens can't fit inside a screw-mount hole (the way a screw-mount lens can fit inside an M-bayonet) because M is bigger, and so the lens cannot be positioned close enough to the film plane to focus at infinity.