Gary, Great questions and thanks. Yes 58mm is the correct size and will fit perfectly. As far as flat Vs. convex it is a question that is harder to answer. It depends on what you read as this debate has been going on a long time and I see no clear cut winner. So it seems to me to be a matter of personal choice and me personally I have always used the flat one and been happy with that. But you may want to read more and see what the discussion is all about.