Originally Posted by polyglot
M39 to M42 adapter would give you lots more options, maybe including a camera you already own.
The m39 I have is for rangefinders with a shorter distance to film plane
m39 for Zenit SLR's would work on my 5D, and I have an EOS adapter but it's great for macro work as I only have 1' of usuable distance.
5x7 Eastman-Kodak kit / B+M 135mm Zeiss Tessar + Compur Deckel
RB67 Pro S /50 4.5 / 90 3.8 / 180 4.5 / WLF / prism finder / polaback
FED-2 / 50 2.8 Industar 26m / 85 f2 Jupiter-9
Canon 300v / A2