Originally posted by rogerstg I took similar test shots at appx 20 ft and did not see a focusing problem. The lens is a bit softer at 2.8, but that was only slightly noticeable when viewing small writing at 100%. I have no complaints in this area.
I tried manually focusing and got better results. They looked the same as the f5.6 AF shots. That pretty much eliminates the optics as the problem. The question remaining is whether it is the AF system within the lens (calibration?) or within the camera body.
Since the camera focuses properly with other lenses, and this lens in settings other than infinity, I suspect that it is not the camera's AF system.
While I'd classify myself as an experienced amateur in manual and semi manual SLR photography, I'm a newbie with DSLR AF systems and what I should expect. I wonder if these results are within reason? Looking at the uncropped pics on my monitor (~ 11x14" at 30%) of the good v bad shots, I discern a slight difference, yet at 100% the results are obvious, as shown above.
Any thoughts from experienced DSLR users of premium lenses?
I have found AF to be a hit or miss thing with Pentax DSLRs. My film cameras were better in some ways, but worse in low light as they had older generation AF systems.
I have a 31ltd that works fine on my DS and K100D but is almost never in focus on the K10d's I own. My 16-45 seems good on all bodies as does my 50-200. It is quite frustrating.
It is also harder to manually focus using the APS sized viewfinder and only the matte screen, so that isn't always a solution either. I have considered a katzeye screen, but you lose the spot meter and I use that feature quite often, so that will not work either.
To be fair, if you visit the brandx forums at look at Nikon and Canon, they have the same problems although they have a better reputation for focusing properly. There are many reports of lens to lens focusing issues and other AF problems on non-Pentax bodies so I am not sure if Pentax is really that much worse in terms of focus accuracy. I think the other brands, and even some older Pentax bodies do focus faster than Pentax however.
I think Pentax can calibrate a certain number of lenses to your body, but I am not 100% certain of this as there is no official information about that service. I seem to recall that Pentax offered to do this for Ben when he had some focus issues with his K10Ds. You might try contacting Pentax to see what they can do. I would call them as I have never received a single response to amy email inquiry I have ever sent them when I have had problems with my equipment.
Ray