M42 and Canon FD to M39 adapters

I've seen a couple of adapters for sale recently:

 

M42 to M39, allowing you to mount an M42 lens on a LTM body.

 

Canon FD to M39, allowing you to mount Canon FD lenses on a LTM body.

 

While these may physically work, can they optically work?!? Does

the registration distance go to hell? Can you focus to infinity???

 

Thanks!

If the adapter is designed properly, the lens will focus correctly at infinity, and all the nearer distances will be just as accurate on the rangefinder body as on the SLR. But there will not be any coupling to the rangefinder, so it's zone focusing only.

 

Any lens built for a SLR should be adaptable to a rangefinder, since SLR bodies have to be thicker than rangefinder bodies.

I have had one that mounts Nikon SLR lenses on screw mount (and then with an adapter to M mount) for years. Works fine. You must estimate the distance however which is no problem with wide angle lenses.

The Canon Adapter is "Adapter B" it was made to allow the newer wide angle SLR lenses to be mounted to their rangefinder cameras which have the same thread mount as the Leicas. There is also an "Adapter A" that goes the other way around. These are also used with some Canon Macro equipment and to allow third party macro equipment to work.

 

The film registration for a LTM camera is 28.8mm for a FD mount camera it is 42mm the adapter fits perfectly inbetween. I have used my Canon FD 20mm and 24mm lenses with great results on my Canon Model III and Leica IIIg. At about a 35mm focal lenght the zone focus starts to show it's limits unless you are well stopped down.

Thanks, everyone!