I bought a K-5 with DA 18 – 135 a couple of weeks ago. I have installed firmware 1.03. After taking some portraits of people where their ears were sharp but faces soft, I used the auto focus fine tuning to adjust it. To test the focus, I took pictures both of curbstones across the street (StigVidar's tip in an old thread I found) and a box of matches standing on a soft carpet (lots of fine detail). I suggested this fine tuning to someone else a few days ago on this forum, because after performing it I get very nice and sharp portraits.
Now I have taken some more pictures, many of them outdoors on far-away things. When using the lens’s shortest focal length (18 mm), I noticed that things looked slightly soft, and that things closer to the camera were sharper. Turning off the +4 focus fine tune I had set earlier made it better, so I tested it more thoroughly and ended up on the minus side of the scale for the sharpest pictures.
To summarize: with no adjustment made, there is a tendency towards back focus in portrait situations, and a tendency towards front focus in landscape situations. I can not compensate for both of these at the same time in the fine tune settings. This is all with natural light (btw, I get sharp portraits with the +4 setting in tungsten light also).
Is this something one could expect from a phase detection auto focus system with a zoom lens if something is not calibrated, or is it very strange (unusual)? Is it possible to get the camera and lens calibrated to maximize the focus accuracy at all focal lengths?
Thanks in advance!
/Jonas
Last edited by hjb981; 05-02-2011 at 06:39 AM.