See: http://slrgear.com/reviews/showproduct.php/product/1384/cat/46
The measurbation results seem to be in line with what PhotoZone found long time ago. I now understand why Pentax Germany replied Klaus that the lens under test was "within factory specs"! :-o
If we compare further of the above against those of the original Canon EF-S 18-135 IS, the new Canon 18-135 IS STM and the Nikon 18-135 DX by the SLRGear, the Pentax results are really pathetic.
Still, I like my DA18-135, maybe the lens IQ, especially the image corners, are not good at close distance, where a test chart is usually placed.
Related:-
Updated: Some Recent Random Snapshots of Mine
My Practical Review on the DA18-135
Latest Pentax Reviews: DA18-135 and K-5 Vs 7D