Originally posted by Rudy can someone explain why it is thought that is the Sigma lens focus issue if he says he is having similar issues with his other lenses?
I thought back focus issues when I heard it was with the 70-200mm.. then read further and said soft images with other otherwise not so soft lenses and wondered.
Either there is a back/front focus issue with all of your lenses (possible), the photographic technique needs some tweaking, or there is something wrong with the focusing system of that particular K-5 body.
Or a combination of the above.
At this point it is easier to just calibrate the 70-200 and see if that resolves the issue. If not, go from there (checking technique or considering the body has an issue).
That said, this issue can occur on any manufacturer's system. I mean there are hundreds of us on here sharing images and enjoying our Pentax cameras, so obviously we all don't have faulty systems producing soft images that we are living with. If it is a focusing issue it can be rectified one way or another.
On some (such as the Canon 60D) you can't even adjust back/front focus!!! I think you have to send the lens into support for adjustments (or find one that doesn't have the focusing issue). At least with your K-5 you can make those changes.