Here is the proof again, with photos shot at the same time on a test chart. The remarks made by the OP are clear and self-explanatory:-
http://forums.dpreview.com/forums/read.asp?forum=1036&message=36997087
For quick reference, below are the directly linked pictures from the DAL and the DA II:-
(Above: K-x + DAL 18-55, Click to Enlarge.)
(Above: K-x + DA 18-55 II, Click to Enlarge.)
And, quoted, for what the OP observed (and it's so obvious indeed):-
"First, the DA 18-55 II lens. Note the better edge and corner sharpness compared to the kit lens supplied with the K-x, the DA L 18-55...
The image below is from the L lens, and is not corrected. The two correction functions don't help to correct edge focus - well, if they do, it's not noticeable in my images. I tried all variations.
Even the centre focus drops off towards the edges. Oh, and it's even worse wide open. I'm really trying hard to be nice to Pentax here... "
In short, those newer "plastic wonders" of Pentax could suck! And that all depends on your luck, no wonder! :-( ;-> And afterall, the Pana delivers the best result!
"The image above was auto-corrected in cam; the two settings take around 5 seconds to process and correct for curvature and CA. This slows the camera down immensely, but produces a square, almost error-free image."
"Panasonic get criticised by many for including geometry and CA corrections in-camera - they are applied in every shot. The wonder of all this is that it takes no time at all, in a Panasonic (not 5 seconds like a Pentax), to process these corrections."
As I also have the Pana GF1, I can firmly tell that what that guy says is true!
Some brand defenders would yet argue that the K-x is not the uppermost model of current Pentax DSLRs, so they should see what a new K-5 user reports on the same issue, below!
K-5 Continuous Shooting Does 3 Frames Only! If and When..
Read Also:-
Standard Zoom Mega Shootout! (DA Vs FAJ Vs DAL Vs SA Vs FA!)
(AF) Lens Matching with the Navy K-x