Originally posted by abruzzi I don't have many taken on my K-3 II yet, but before I decided on my frist lens for the camera, I looked at the "focal length (35mm equiv)" of the 12k photos taken over the years on different point-and-shoots, and the vast majority of them were 50mm or less, and the bulk of those were close to 28-35mm. My years with a Nikkormat FTN (that I still have) my only lenses were a 50 and 35, and I always much preferred the 35mm. It seemed more natural. So 35mm in film/full frame terms is my favorite. Which means I need to find a 24mm prime for the APS-C sensor. Unfortunately there only seem to be two with autofocus--the Pentax 24 F2 which is a bit pricy for a lens that always looks beat up (bad choice of color) or the Sigma 24 F1.8, which I've only seem for sale once and I'd love to see for sale again.
Sigma also had an AF version of the 24mm f/2.8, but it is becoming more rare these days. Still, when you find it, it's cheaper than the 24mm f/1.8, and it is very good optically by all accounts.
I find that for most uses, AF isn't necessary on APS-C for a 24mm lens. A lot of times I just set it at f/5.6 and hyperfocal and go. I've been toying with some manual 24mm manual lenses for a couple years now and currently have two - a Cosina (Vivitar) and a Tokina, though they seem to be exactly the same lens, down to the coating's reflections. It is a good performer - the same lens was even sold as a Carl Zeiss Jena (!!). I recommend it, very good lens, very sharp especially at longer distances which is what you want in a 24mm lens. It does need a hood because it flares up very, very easily.
24mm on APS-C would be my 3rd favorite focal length, after 50mm and 35mm.