Hi folks,
First of all, I hate testing and pixel peeping, I do it only when I notice a real issue in actual use. I do enough testing in my day job as a developer.
So, I have a K5 IIs and a Sigma 10-20. For a bit of background, I used to own a K5 and another 10-20 until last year, when I had to sell my setup. I then used an Olympus OM-D for a while. I am now back with the Pentax.
Here's the issue I'm having, and I'm wondering if anyone else here has noticed something like this: When using the lens at the wide end, it seems that the combo has a lot of trouble focusing in the distance. I first noticed it when I realized the picture sides were noticeably softer, or less in focus than the rest, often accompanied by a slightly sifter center. It doesn't happen all the time.
What I've noticed is that when auto focusing in the distance (let's say on the mountains), the lens seems to want to settle on some hyperfocal distance rather than actually focusing over there. The ring will go to 3ft/1m. When this happens, well, then that's where the best point of sharpness is, and you get more blur at infinity, and the sides suffer even more (it seems a slight misfocus of the center is way amplified when reaching the sides of the picture, and I'm not talking about the extreme corners here), beyond what's acceptable on an UWA lens.
If I switch to 20mm, there doesn't seem to be any issue there, and the scale will jump to near or at infinity, as it should. When properly focused, the lens is pretty sharp. If I then switch back to 10mm, generally the AF will not move and just stay there near infinity.
So, I'll specify that my previous 10-20 on the K5 had no such issue and worked really well (I have also compared with shots I took last year and reproduced them with same settings).
Also, this is a replacement as I sent back the first copy for this same issue and also noticeable back focus at 20mm. This second one has lens backfocus.
So, wondering if anyone has seen this issue, or perhaps an incompatibility between the K5 II's AF system and the lens, or similar behavior with an UWA zoom from another brand.
I will try to do some testing with manual focus in the morning. I'm not sure about alternatives. I'm a wide angle shooter. The Pentax 12-24 is obviously not as wide (and has a goofy hood, as an aside) and is way more expensive...
Last edited by LeChuck; 04-30-2013 at 08:25 PM.