Of all of the FL/FD mount converters offered by Canon, the Converter P (Praktica/Pentax) is probably the most common. If you're patient, you should be able to find one on eBay or another source for a reasonable price (i.e., $20 or less). I've used this converter and can confirm that it provides infinity focus. The only potential issue is that, on M42 lenses with the automatic diaphragm but no A/M switch, you have to lock the diaphragm actuating pin down in order to shoot at less than full aperture.