Caution large differences in quality (Optical Power)

Currently I use a Tamron 18-200mm on my Pentax K20.
That you have to do in this appearance with the large zoom ratio compromising on optical quality was already clear to me, however, was lucky to get a very good look.

My reasoning went in the direction of a lens to buy, that may have a not so large zoom range, but is better in the imaging performance.

The focal length of 18-135 mm is actually ideal for this task.

When my friend who owns a Pentax K5 with the 18-135wr I could extensively test the lens on my K20D and was absolutely delighted when it comes to processing, handling and optical imaging performance.
The lens is super fast and accurately what the autofocus angeht-
The high degree of transparency and the enormous sharpness is impressive.
He was lucky enough to snag a really good lens.
The only fly in the ointment is that just heard this lens my friend, because I was not able to find a reasonable appearance of this series so far in 6 attempts. All lenses I tested the image quality was equal to or even below the power, the "cheap Tamron" (159) delivers my. That can not be true !!!!
Pentax seems to throw each lens produced on the market, whether it is inferior or not and of this simply is absolutely too high a price.
I find it very unfortunate that the company now as procedural.
An objective of this series I will probably not buy.
Interested I can only strongly recommend that: "Try before you buy"
the quality differences are simply too great.

Wilfried K.