Originally posted by chongmic Is there significant different between optical quality of both series? Let say on a 135mm lens.
Pentax released the M series in 1976 to keep up with Olympus in compact 35mm lens/body design, mostly for the consumer market. The M series lenses were not improvements in optical design over the K series lenses they replaced, they were just smaller. It wasn’t until the A series lenses that you saw optical improvements like the A*85/1.4 or the A*135/1.8 to name a few.
That’s why you don’t see M series lenses fetching much in today’s market, like you do for some K and A series lenses. (Exception the M2000mm reflex) They’re optically good but I wouldn’t consider any M series lens a classic like a K50/1.2, K28/2, A* or FA ltd lenses. The one exception would have been the prototype M35/1.4 which is based on the K28/2 optical design and featured floating elements. The M35/1.4 however was big and had a 58mm filter thread, not exactly a typical M series lens. That’s most likely the reason it never went into production, as well as its most likely high selling price.
As for the K28/2.0 vs the M & A28/2.0, there is no comparison. The K28/2.0 is like the K50/1.2, they are classics and are unique lenses. It’s not about sharpness, it about the effects these lenses can produce when used in a specific way. There is no M series lens that remotely comes close to the K50/1.2 or the K28/2.0 optically. Once you try these two lenses you’ll understand.
Phil.