This is interesting:
A picture take from the computer screen
Again Pentax K10D, Sigma 18-200
Common settings: 200mm, 1600 ISO.
Camera stabilized on a tower of CD boxes :-)
Attached picture is a 100% crop; the "GHz" was more or less in the center of the original picture.
First with F/5.6, 1/90sec
Then with F/38, 1/2 sec
I guess my problems are now reduced to either:
a) the lens (bad resolution at large apertures)
or
b) focussing problems (the F/38 increases the DOF, which masks the focus error ? )
I still don't understand why the blur is more pronounced on the vertical lines...
Erik.
Forgot to mention: SR was off in both cases.