Since nobody has yet posted the obvious, THE on-line pentax K mount reference is Bojidar Dimitrov's K-Mount page at:
bdimitrov.de/kmp Which tells pretty much everything about every K-mount lens ever made. I tend to get my used K-mount lenses from KEH.com because they have a very large selection and are fairly reliable. There are cheaper ways to buy pentax lenses online. It's hard to find a store outside of major cities that handles a worthwhile collection of used Pentax lenses, leaving online/mail-order as the best solution in most cases. IIRC you were looking for a 35mm f/2.0, of which Pentax made a bunch of versions (K, M, A, and autofocus FA) all of which are quite good. They'll all work on the ME series cameras. You can also fit old Pentax "Takumar" screw mount lenses with an adapter but there's not much reason to do so. In general, "M" series lenses are the easiest to find because they appear to have been made in the largest numbers, plus they don't have the reputation and collector appeal of the older,heavier "K" series (actually labeled "SMC Pentax" with no "K" label, but introduced to go with the "K' series cameras) and don't have the useful electronic connections of the later "A" series allowing full functionality with cameras made after 1983. DJE
