Canon 40mm Slimline Filters do not vignette on this lens. Standard size 40mm filters do vignette, in my experience. I prefer to use a filter and hood with this lens, so I use a Canon 42mm A Hood, marked 50mm F1.8, 35mm 2.8 and no vignetting at all. Kodak Series VI filters are plentiful, used to be sold by the pound. They fit tightly (no rattle) in this hood, or you can go with the Canon Series VI, if you are a purist. I added a Schneider LF leather lenscap, as I needed a tightly fitting lenscap to shield the meter in M5. This is a good workable well-tested combination. I have never had any successful results using adapters with this lens, just about everything vignettes in my experience.