Summary: In the center, this is a 5 star lens at all focal lengths and f-stops. At the right and left sides it is a 3-4 star lens. In the extreme corners it is a two star lens and deteriorates to a one star from 100mm to 135mm.
Summary: I never realized how important WR really is until I spent time at Niagara Falls. I did not dare to take my camera out because my WR lenses are 50-135 and 55-300 which are too long when I was walking underneath the fall.
Summary: I own 9 compatible Pentax lenses and this one has the most personality of them all. The 18-135mm basically tries to keep a sharp center (even at longer lengths) but has soft corners at most focal lengths and apertures.
Summary: This lens has hardly been off my K3 since I got it. Great for a walk around lens. Doesn't rate with my Limiteds or Star lenses but very good IQ and is weather sealed. Great range and focus is fast.
Excerpt: I use this as my everyday lens for vacations and around the house for my family and pets. After using it for a couple of years, my first copy got dropped five feet onto a wood floor and ever since has been not so sharp (still works though). So I got a second copy to replace it to use on my K3.