Originally posted by pentax_rob Do any offer the "glow" usually associated with Leica or the 3D Pop of Carl Zeiss?
Some, but they don't always come cheap. Look for some fast Takumar lenses. You can also get actual Zeiss lenses in m42 or K-mount (East German Jena Zeiss, or the West German, more modern Zeiss), as well as Soviet Zeiss clones, like Helios 44 series. Samyang makes some great modern primes at affordable prices, but manual focus (Samyang also sells lenses under other names like Bower, Rokinon, Walimex and others, depending on your region).
You should first decide how manual do you want to go. K and M series (manual, but lenses have aperture lever which the camera can move), A series (camera can move aperture lever and also knows the aperture value), or F, FA (practically fully automatic, like modern DA and DFA lenses)? Is the dead K-mount okay (found in some third party lenses like Mitakon, it is fully manual, essentially like a preset m42 lens) for you? How about buying an m42 adapter and using those lenses? Some classics there.
If you don't mind some difficulty, try K and M series. A is a little easier to get the hang of. F and FA are super simple
m42 lenses can be real gems, as well, but you need an adapter. I recommend the genuine adapter, as it has very little chance of failure. We have had some nightmare threads where people got their cheap adapters stuck and so on.
Anyway, you might want to start with one of the
Pentax 55mm f1.8 lenses. These tend to have quite nice rendering. Or
Helios 44K (Helios 44 come in many versions, some with different mounts). Or Zeiss Flektogon 35mm (m42, allows near focusing, has is own
thread). You can also look at older fast 50mm lenses, really difficult to go wrong with any of those.
You might want to check the Soviet lens club, as these tend to be cheapest and some still have great IQ:
https://www.pentaxforums.com/forums/122-lens-clubs/31430-soviet-lenses-club.html