The photo below is if the bottom of my Vizio television. When I'm bored, sitting on my bed, fiddling with my various lenses, one of the things I'll often do is zoom in, focus on, and snap a photo of the silver grill with all its holes. Last night I tried that with my K5, and it would rarely if ever achieve focus. Ditto this morning, with additional light coming through the window.
Probably five times out of ten the lens will twitch and the camera will indicate focus lock, but its so blurry that you can barely tell there are circles. That's in the viewfinder even. It's not even close to appearing in focus. Two times the lens will hunt a bit then the camera will indicate focus lock, but the image will be that blurry. Two times the lens will hunt a bit and the camera will indicate it can't lock focus. The remaining try it may achieve focus lock or it may twitch and indicate it can't. If I swing the lens to the DTV logo, or up to the black edge of the screen, the camera locks perfectly, so it's the camera having trouble with the grill. The thing is, my K-10D locks focus every single time with every lens. It has no trouble with the grill at all.
I have tried this and it's repeatable with a Tamron 70-300, Tamron 70-200 2.8, Tamron 28-80, Sigma 18-50 2.8, and the Pentax kit lens. In all instances I was close enough that the grill filled the viewfinder, but far enough that I was well into the focusing range of the lens. Lighting in the room is above my head, about seven feet from the tv grill, and is four 100 watt (equivalent) fluorescent bulbs, plus (this morning) sunlight coming through the window. The K-10d will focus with only one bulb in, so I don't think available light is contributing to the issue.
I'm aware of the notes in the manual about certain surfaces being hard to achieve focus on, but I'm shocked that this could be one of them, especially when it's so easy for the K10.
Can anyone else try to duplicate this so I can confirm whether it's an issue with my camera or the K5 in general?