The K-5's center focus area is relatively big. I was curious about how much bigger than others, so I compared it to the Nikon D90's, using images of both viewfinders taken from their user manuals. The Nikon manual specifically shows the width of the focus area. For the K-5, I used the circle at the center of the viewfinder, since that's been identified as the focus area in posts here, and I've confirmed it myself.
Focus area widths, as percentage of viewfinder width:
- K-5 - 8%
- D90 - 5.8%
- D90 - 6% of final image width, taking 96% viewfinder coverage into account
That makes the K-5's center AF area about 1/3 wider than the D90's.
This was a rough test, so please take it for what it's worth.
Jeff