what has a 43mm filter thread?

[Jack Campin <jack@dcs.glasgow.ac.uk>]

I have a whole pile of 43mm filters (B&W and Olympus, pretty good) bought
for an Olympus Pen-FT system.  I believe there is some lens in the Leica
line that takes these.  If so, what is it?  I'm intending to get rid of the
Pen-FT stuff (it was fine where I bought it - Auckland - but I don't find
their dim finders usable in the hyperborean gloom of Scotland) but if the
filters are going to come in handy in the future I'll hang on to them.

Plug for yet another screwmount lens: the Schneider Xenogon 35mm 2.8.  Mine
is internally filthy but still works pretty well.  Takes A36 filters, though
these can vignette it.  Mine cost 70 pounds about 3 years ago.

I second people's recommendations for the Canon 50mm 1.4: I have one and
it's VERY sharp and contrasty.  It cost a bit over 100 pounds, consistent
with the $200 figure other people have mentioned, though I've seen them
advertised in the UK lately for as much as 200 pounds.  Word seems to be
getting round.

I also use a Canon FL-mount 19mm with an adaptor.  Doesn't couple to
the rangefinder, but at that focal length it hardly needs to.  Is this
any different optically to the Canon screwmount 19mm?  It doesn't seem
to be a retrofocus design (has a huge internal projection that would
require mirror lockup on its intended body).  I've used this a lot for
up-the-nose pictures in demonstrations and for cities like Lisbon, where
narrow lanes and vertiginous stairways are the norm.  Vignettes a bit at
full aperture and a lens hood is impossible as it gets in the way of the
finder; fortunately it's reasonably flare-free.

Nobody's mentioned any lenses longer than 90mm.  Is a 135mm Hektor at all
reasonable if you wear glasses?  The frame on a V100H multifinder (the most
user-hostile piece of Leitz gear i've ever used) is minute - is the 135mm
brightline finder any better?