Unimpressive sharpness. I happily substituted a Pentax 28-105 f3.2 and a Tamron 70-300 for this lens. Both are significantly sharper although the Tamron loses sharpness rather quickly past 200 mm and is quite a bit larger. After reading some good user reviews, I again matched the Pentax 50-200 against other lenses and found that my original negative conclusion was correct.

My first reaction to the lense was (so small) - I wonder how it plays. To my surprise I didn't see a trace of CA at all. That's well above what I'd expected for the lense of that price. AF speed is good for not IF lense. Front element is not rotating, which only adds to the overall positive feedback to this lense. What first looked like toy in my hands appeared to be very good performer.

http://roman.blakout.net/?blog=20070329160524

Compact, light, very good quality for the price. I tried and returned a Sigma (for more money) before buying this one. A great lens when I want "easy" and don't need the low-light capability of my older primes.

A very compact and efficient telephoto zoom. The optical quality is very good and the price is amazingly low. Thoroughly recommended.