er... check the prices of Leica lenses - it's generally not a make to "experiment" with unless you've deeper pockets than I have...
That said, the Leica Thread Mount was also used by lots of the Russian Cameramakers - My old "radioactive" Industar currently fitted on the FED3a is one of these screw mount ones, and cost me the grand sum of £3 plus postage and even came with a large heavy-duty rear lens cap (often referred to as a broken fed 4
)
Personally, I'd just get a good quality Canon FD 50mm f3/5 macro lens, stick that on the front of the bellows and take it from there.
As to mounting the FD lenses direct to a EF mount Canon body, you could well have problems. The mounts are essentially pretty much incompatible, because the "registration distance" (distance from the mount plate to the sensor/film) is shorter on the FD than the EF - which, in plain english means that if you put an adaptor on the front of the EF camera, then fit the FD lens, the lens won't "focus to infinity" - i.e. it'll work at close distances (maybe a couple of metres, it's been a while since I used one, and I forget exactly - but certainly not 10 yards or so...) but anything further and it won't work. To get around that, there ARE special adaptors for FD>EF lenses that are basically like a small "teleconverter" (they work at approximately 1:1.2 iirc) so convert a 50mm f3.5 into a 60mm f4.5 but they WILL focus to infinity, at the trade off of reduced image quality because of the additional lens in the adaptor...
Here's what a
"plain" FD>EF lens adaptor looks like... this one won't focus to infinity, but WILL have better image quality for macro's because there's no lens to degrade the image
and the
"special" FD>EF adaptors look like this... to be honest, the quality of the lens in these adaptors is "ahem" variable... but I'd generally say tending more towards the "terrible" than "acceptable"
Canon actually did bring out their own adaptor for this purpose, but they're rarer than rocking horse dung, and cost probably as much as a good second hand EF mount macro lens...
Basically, Canon did their level best to make a clean break between the old FD/FDn standard manual lenses and the EF of the Film (and eventually Digital) Autofocus kit. And with the exception of macro use, I'd recommend that you pretty much go with what they did...
