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

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.