Originally posted by wlachan I think M was the last high quality series lenses Pentax made then the build quality started to slip. However, optical designs have improved greatly on zooms and colour rendition. The problem with today's AF lenses is their inability to maintain optical alignment due to aggressive cost cutting, loose QC and the way they were built. Still, a good old A prime should outperform 18-250 for corner to corner sharpness. But every lens is different, so they should be evaluated individually. Personally I like how the M lenses feel against A lenses, or any modern AF lenses. Wish I could afford those nice ZK lenses.
I prefer the feel of the M series to the A series for the most part as well. I prefer the feel of the K series to any bayonet mount Pentax ever made. That said there are some awesome A series lenses: A* 85/1.3, A* 200/4 macro, A* 300/2.8 and others which are amongst the best Pentax ever produced. I wouldn't buy a zoom from K, M or A series which, although useable, just don't compare to modern zooms.
Tom G