I asked this on a different board and didn't really come up with a satisfactory answer. I'm trying to figure out if the problem I've been having is lens specific or if it's my camera.
Can anyone who has a better understand of what causes back focusing problems explain to me if it's possible for my K110D to correctly indicate focus on my two manual lenses, but seem to skew backwards on my two auto-focus lenses? I just did a quick test, and it seems like I can do a better job by hand than my autofocus does. Actually, after typing that sentence it occurred to me to compare the same lens in manual and automatic focusing modes.
Not sure it'll really come across when resized for the forums, top is automatic, bottom manually focused:
I got a little paranoid when I was going through pictures from a recent shoot and was just convinced I COULDN'T have screwed up the eyes that much on my own. I realized in several of the pictures that I was SURE I had recomposed properly that the eyes weren't clear but the necklace around her neck was tack sharp, so I went and grabbed the backfocus test chart from
Nikon D70 Focus Chart and did the test as carefully as I could with multiple lenses and realized the results were inconclusive. Then I realized it seems like my old primes were focusing fine but my two zooms weren't and I was paranoid I was doing the test wrong. So I compared manual and automatic on the same lens, and found that if I used the focus indicator manually focusing my lens, it was right, and autofocus wasn't, which boggles my mind a little bit. I also can't tell if it's JUST the Sigma lens messing up or if it's that the kit lens doesn't have a narrow enough depth of field wide open to be as noticeable. In order to try and conclusively test if I was messing up the execution of the test, I also tested with a different chart I found with the round light/dark oval in the middle with a level camera with the chart set up on a wedge. The results were even more noticeable there but I don't have those images handy to show.
So that brings me to the question: How is it possible for the camera to "know" what focus is right, and then set the automatic lens incorrectly? I don't understand what is really CAUSING it, and what I need to try and get fixed.