You need a 3rd party lensmount adapter. There are lots of these on eBay, but they are of varying quality. Go searching for reviews on m42-Canon EOS adapters to find which ones are best - some will not give you infinity focus because they're too thick, others may be likely to get stuck on your camera (I had that happen, frighteningly, on my Canon 5D with a Contax MM/Canon EOS adapter, and it bent part of the focusing screen retaining clip by the time I got it off). This is one thing NOT to cut corners on because solving the problem(s) a cheap one can cause may be far more costly than the better grade adapter.