12-24 On Full Frame

In answer to David's question - neither.

The gallery picture is only a minor crop to straighten, rather than crop to APSC. The 12-24 is not ff compatible but it's not bad to use. Sharpness to edges is surprisingly ok. Centre sharpness is plenty good enough. So knowing the limitations then it's perfectly usable on ff. It's main issue for me is chromatic aberration, but that is no worse than on crop sensor. From 17-24mm it doesn't vignette.

I don't use it that much - the 31mm is my go to landscape lens. I would have gone for a 15-30 but for the required investment in a whole new filter system. I was hoping that Pentax would make the wide prime (20mm?) on the roadmap - but that has been kicked back again so probably won't ever arrive. Also annoying that Sigma won't make their lenses in K mount. So my preferred option is the Irix 15mm (if you can find one) to use alongside the 31mm.

The following examples are all taken with the K1 and 12-24 with only a small amount of cropping from the long edge, or none. I am to blame for the dark edges, not the lens. Furthermore, as none of them are ever likely to be printed at all let alone printed large then quality perfection doesn't matter. Although I reckon they would stand up to all but the pickiest critic (which is me anyway). The only pictures I'm likely to print with this combo are the pierscapes, where edges and corners are featureless so the 12-24 works just fine for those:

Thank you Adrian, that's really helpful. I'm teetering on the edge of going K-1, but the lens investment required is putting me off at present. It seems at least I could get good results from my 12-24 in most circumstances, so that's good to know.

Regards
David

Thank you for that information.. Interesting for those of us that print very little.. Great pics too..

So true your filter comment. For the 15-30..

I struggle to get good results below 16mm om the DA 12-24 without severe vignetting on my K1 but at 16mm - 24mm it is an excellent lens. Still my favourite on a crop. Using man maths, I had to buy a Venus Optics Laowa 12mm for the K1. It is very wide but I'm very pleased with it . Similar IQ to the DA 12-24 although the flare is worse. The distortion is excellent on the Venus if that's your thing. I'm waiting for Pentax to bring out a scaled up 12mm to 24mm zoom for the K1, The Venus is tiny for what it is, so I expect I'll keep it.