I have the FA 28-70mm, it is by far my sharpest autofocus zoom. This is a light weight lens with a couple of flaws such as the not-so-great feel (feels a little cheap) and the rotating front element which makes polarizers a challenge, but it makes up for this by being a very sharp lens. I think this is second only to the FA* and DA* f2.8 lenses for image quality, while being only a fraction of their size and weight (52mm filter ring). Good find, I only paid $75 Canadian for mine at Henry's used department in Toronto.
Riverview, NB, Canada
Pentax *istDS, K3:
FA 50 f1.4, FA 28-70mm f4, Tamron SP 70-200mm f2.8 Di, DA 10-17 f3.5-4.5, DA 14 f2.8, DA 16-45mm f4, DA 18-135mm f3.5-5.6 WR, AF-540FGZ
Olympus E-P5, OM-D E-M1(X2): 9mm to 150mm lenses