Sorry...for my english but i tried my best
@emr....Your impression is correct.
translated from "FotoMagazin Special Februar 2009"
Pentax da 4,0/16-45mm ED AL Setting
High quality, very good operability,very good scattered light protection,close-border good.
Imaging capacity
clearly higher-contrast and higher resolution than the da 18-55 mm. errors at 16/28mm with max. aperture. stopping down improves the image contrast and the resolution.
Vignetting
visibly however very homogeneous
Distortion
barrel distortions at 16mm only. altogether very well
Optic :
81% at APS
Mechanic:
81%
FotoMagazin note: Very good
Vs.
Pentax 2,8/16-50 DA* ED IL SDM Setting
Very high built quality, very good operability,the front element does not rotate,metal bayonet, MF-modus
Imaging capacity
performance is typical and fair at f/2.8, good at f/4 and very good from f/5.6 onwards.
Vignetting
at 2,8/16mm strong, at 50mm noticeably , stopped down very good
Distortion
at 16mm very strong, at 28mm excellent, at 50 mm well to very well
Optic:
73% APS
Mechanic:
88%
FotoMagazin note: Very good