[lesmore49]

Great tip on the black dot thing. Thanks, I will do that.

And you might be right about using this (or any other AF lens) in the landscape. There's so much stuff (branches, snow, stumps, grasses, logs) for the AF system to latch onto that it might be missing what I really want in focus. So that's why I started using center spot AF to see if I get better hit rates. I like that this lens supports quick shift, as fine tuning focus is easy. So the lens may indeed be fine, it could be just user error.

You're welcome. I also use the spot AF setting a lot for these type of photos. I think part of the issue with the 12-24 lens is that it has such a relatively large field of view as a wide angle. At 12mm , etc...it does cover a lot of real estate. Although that is just a guess on my part.

Another thing I do, when taking pictures of again vintage cars with large hood areas without AF spots.....is I sometimes will see a AF point...such as the hood ornament on the car's vast featureless hood, and I gently push down either the shutter button...without pressing the shutter completely down so I can 'lock' the focus, or I focus , then put my finger on the AE-L button (AE-Lock) when I find a AF spot to lock the focus, and then compose my picture of the large area without a AF point, but still within the same focus area, and take my shot.

[Viking42]

Another thing I do, when taking pictures of again vintage cars with large hood areas without AF spots.....is I sometimes will see a AF point...such as the hood ornament on the car's vast featureless hood, and I gently push down either the shutter button...without pressing the shutter completely down so I can 'lock' the focus, or I focus , then put my finger on the AE-L button (AE-Lock) when I find a AF spot to lock the focus, and then compose my picture of the large area without a AF point, but still within the same focus area, and take my shot.

That's pretty much what I do as well, except I have disabled the shutter button focusing and only use the rear AF button. Works great, at least for the static subjects I normally shoot. If I did a lot of moving things then I probably would enable shutter button focusing again, or use AF-C mode.

[Ex Finn.]

That defeats the purpose of having a relatively high-qualify camera and lens. A lens could be obviously decentered or have some other defect if you don't check for it, and you wouldn't notice until you happened to take a photo that showed the problem. It's no different with testing your camera for noise at different ISOs: you want to know what your equipment will do based on what you find acceptable or not. And most of us find our lenses have different capabilities at different apertures: there are some photos we would only attempt stopped down, and others we might be willing to take wide open. There's no way to know that without testing. You don't want to learn your equipment limits with important pictures.

Should have been more specific with my comment.
If the lens is not exhibiting obvious flaws in image quality without pixel peeping, then use it, none of them are perfect.
If my lively hood depended on my image quality, now I might have a different opinion.

[Viking42]

Update here: it turns out the lens was off on infinity focus, so with the help of some of the PF crew (here: Infinity adjustment, DA 12-24 on K5ii - PentaxForums.com) I was able to test and tweak it. It needed +5 focus adjustment at infinity and (thankfully) the same at close focus (~1.5 metres). So all is well. I will take it out for a hike this afternoon and give it a good field test too. Looking forward to seeing what this famous lens can really do now that it's all adjusted.

Thanks all for the help and advice here.

Best,
Svend