There's been a lot of speculation about the size of the AF points on the K-3. One of my biggest complaints with the K-5 I own is that the focus points are so large that I'll often focus on an unintended object behind my subject due to the size of the focus points. I said my initial testing seemed to indicate the K-3 points were smaller, but the official review here said they were about the same. So I thought I'd set up a more controlled test.
I taped a piece of wrapping paper to some curtains hanging in my house. This was to provide a higher contrast background than the brown curtains. Then I used a lightstand and a boom to hold a high contrast focusing target about 3 feet from the curtain. My goal was to create a high contrast focus target, with a reasonably high contrast background. I would pivot my K-5 and my K-3 from the same tripod location with the same lens and try to get a rough idea of how far from center the target would have to be before the camera (set to center spot) would focus on the background instead of the projecting target. My test lens was a Sigma 24mm F/1.8 lens set to F/2.0.
I took hundreds of frames, moving the camera slightly up, down, left, and right to try to figure out the boarders of the AF zone. The results confuse me.
For the K-5, I estimated the center focus point to be approximately 200x200 pixels. This is of a frame height of 3264 pixels. That's about 6% of the image height.
For the K-3, I was astounded to measure an approximate center focus point of 520 pixels! For a frame height of 4000 pixels, this would be about 13% of the image height!
I checked my K-3 to make sure I didn't do anything crazy, let set the expanded AF zones or anything weird. But I can't find any setting out of the ordinary. Has anyone else tried such a test? Maybe I need a test where the background is of equally high contrast? Maybe the expanded AF abilities of the K-3 change how it transitions from one focus point to another? I'm really at a loss to explain this.