The EF-M 52mm is part of the rumor, hasn't been introduced and may never exist. The overall diameter of most/all Canon EF-M lenses is 60.9mm or maybe 61mm. That's the "self-imposed design rule" that was referred to. I think that rule is a serious mistake. I own the 30mm f/1.4 Sigma and don't find it oversized with an M5. It's an excellent lens and I'm seriously considering buying the Sigma 16 f/1.4 and maybe the 56 f/1.4. However, for the last 20 years, I've use the f/2.8 trinity lenses on a FF body and it's a bit painful going back to fixed focal length lenses.