Lots of good advise here. If you intend to go hunting for lenses, read this:
PAWNSHOP LENSES (and other used lenses) - A Buyers' Guide. This could also help you evaluate any lenses you buy by mail and are unsure about.
More on the lingo:
SMC means Super Multi-Coated. Commercial lenses are complicated beasts, with numerous hunks of glass glued together or separated by air. Every glass-to-air edge causes refraction, lowering contrast and imparting other nasty effects. So, many years ago, lensmakers learned to coat those surfaces. First one coating, then multi-coating (MC). Pentax chemists worked up superior coatings, called SMC, long regarded as about the best stuff around. Uncoated or singly-coated lenses are susceptible to flare and low contrast, which can lend a nice 'period' effect to pictures -- not so good if you want sharpness and clarity, eh? All Pentax lenses are coated, but those labeled SMC are often the best. But not always -- see the lens review database.
PRIME has nothing to do with quality of lens or meat -- it just means a fixed focal length, as opposed to a ZOOM or vari-focal lens, which works (more or less well) over a range of focal lengths. Modern zooms are exquisite tools, even the much-maligned DA18-55 "kit lens". Zooms always embody design compromises, trying to make the lens work well at all focal lenghts, and are usually weakest at their extremes -- which is where most people use them! Primes have more esoteric design compromises, usually related to speed (maximum aperture) and cost.
DA and
FA are prefixes used by Pentax for lines (series) of lenses. Of the bayonet (PK-mount) glass, the historical sequence generally goes:
K (actually no prefix) and
M, manual focus and aperture;
A, manual focus and auto aperture;
F and
FA, auto focus and aperture, for full-frame (film) cameras;
DA, auto focus and aperture, for half-frame / APS-C digital cameras. There are also some minor variants:
FAJ and
DFA and
DAL. See the lens review database for details.
Have fun!