I'm looking for a collapsible 50mm, or maybe two because I can't decide between size and speed. small/compact lens (f3.5) Leica 50mm f3.5 Elmar Cosina 50mm f3.5 Heliar larger/faster lens (f2) Leica 50mm Summitar Leica 50mm Summicron Cosina 50mm Heliar Questions 1. There are a few ltm elmars, which ones had 39mm filter threads? just the f2.8? 2. Are the Cosina lenses 39mm filter threads, i would think so, but I want to make sure. 3. Anyone have a size compaarison of these lenses? I'm not sure how the Heliar (slow and fast variants) stacks up against the Elmar /Summicron in terms of size.