[Leica] Summitar Filters and Cap

["Mike Durling" <durling@widomaker.com>]

Hey Luggers:

I recently picked up a user Summitar for my IIIf.  So far after two rolls I
like it very much, a little soft wide open but very nice stopped down a
little.

When I got it I tried the clip-on shade from my Summicron and it fit so I
figured ok, it takes 39mm screw-in filters.  I don't actually own one of
these but I needed a cap for the Summitar so I ordered a 39mm screw-in cap
from B&H.  Well, I got it and tried to screw it in and it didn't work!  I
looked at the lens and there are no threads on the inner edge of the lens
barrel. Silly me for not looking!  At least I can use the cap on the
Summicron if I lose the one that goes on the shade.

My question is what kind of filters go on this beast?  There are threads
down inside next to the front element but they don't look very useful.  Is
there a modern equivalent filter or cap size?  I hate to pay collector
prices for these things, and I usually lose the slip-on caps.

Thanks,
Mike D