sick of me yet?
ok, here's what i did. i set the flash exposure at + 0.5. this had a noticeable effect on exposure levels - images are much brighter, and closer what i think they should be. i then took a photo at 6 progressive aperture sizes, starting with the largest possible. on my lens, at 55mm it is f 5.6 . this picture was much improved due to the flah compensation, but still slightly under exposed and dim. the next aperture up - 6.7 - was noticeably better again, the histogram looking pretty much right ( although my experience with histgrams is virtually nil, i'm assuming a nice single peak in the middle of the graph with even fall off both ways is good?). from there on up, not much changed - the next five aperture settings ( f8, 9.5, 11, 13 and 16) were all similar. perhaps exposure level went up a tiny bit across that range.
so what i would say, from all this, is that my lens is not all that flash when wide open. and indeed the pentax literature does mention that light fall off in the corners will occur at maximum aperture for the Da 18-55. i suspect that on mine, it's not just at the corners, the whole frame underexposes. but stop down by one or two levels and it brightens up considerably.
so to the OP, i suggest dialling in a positive flash exposure compensation, see what effect that has, then run a batch of shots at progressive App sizes. you may find that your lens is not great at extreme settings. But there also seems no doubt that the K10D is a chronic under-exposing camera at it's default settings.
well, it's my first day on the forum. this thread has already taught me a fair bit about my new camera. it's been fun, if nothing else.
and if i've gone astray anywhere with all of this, please correct me. i want to learn as much about the camera as possible - no point having something you can't use correctly.
cheers, jason.