Well I ventured down to the Severn Estuary today, with an array of cameras (well two). Spent ages shooting all kinds of wonderful pictures with the K10D and Pentax-M 35/f2 lens and a polarising filter. Most were shot at f16 or f22 to get good depth of field using the hyperfocal focus scale on the lens.
It did cross my mind that the shutter speeds I was using seemed rather high (1/320 - 1/250), but the exposures were coming out nicely balanced and it was too bright to see the little screen display anyway.
When I got home I realized why. The lens wasn't stopping down properly and all the pictures are about f4 or something and out of focus :-( I've just dismantled the lens, and it should be fine with a bit of a clean.
I have a half shot roll of Rolleiflex shots at f16 and 1/15s & 1/8s (using the Rollei's meter and my Weston, with a stop or twos compensation for the polariser), so I guess I'll have to finish it off quickly ... or go back.