I tried my old FD35-105F3.5 on the M. It already had an Mika FD-EF adapter so I could mount it on my T2i. It mounts on the M with the EF adapter.
The experiment went fine, but I haven't really used it yet. I find it a bit challenging to hold still at longer focal lengths with no IS and manual focus. You might need to practice focus bracketing. It is fine outdoors with a high shutter speed, but a tripod or other camera rest can be useful. I did not use it indoors.
Thanks for your sharing.
I have some experience shooting with manual focus lenses on DSlr. Apart from this Canon FD 50 1.8, I have some Pentax, Meyer Optik, Pentacon, Helios, Mamiya,Olympus, Minolta, Sigma, Soligor, Tamron and some other lenses in the drawers, mostly prime 50mm, 55mm, 58mm 135mm. I experienced using some of them on my 40D and X5 with reasonably good results. However, I hesitated using them on 5D3 to avoid debris, dust or fungus (not sure if there are any) etc getting into this relatively expensive camera.
When I purchased my M, I remember somebody somewhere mentioned that the registration technical problem is non-existence and a simple adapter for canon FD mount and Minolta lenses respectively will allow focusing to infinity etc, etc on a M body so I started another round of purchase of accessories to bring these vintage lenses back to life. They may look and work nice on the "M" I hope.
Focus bracketing may not be able to set in manual focus if I guess it right. I am not sure if FD to EF adapter with AF confirmation chip mounted on a EF to M converter will work. Or may be, I should simply order a FD to M adapter and use Magic Lantern Focus peak etc to assist in focusing. Stacking 2 adapters together may create some possible problem - please share your experience if you have any.
BTW, I have today committed to buy a FD 50MM F1.4 for $100 online and hope that it will make a difference comparing to my 1.8
posted on an ice all around day in Toronto