Originally posted by froeschle Knowing the problems of a non-cross type sensor (from e.g. the Z-1P), this could be a strong argument against a K-5 II(s), if one often uses slow lenses and the central AF point.
One needs to bear in mind, though, that the f/2.8 sensor should still work for f/4 lenses. There aren't that many lenses that are slower than this.
Also, given the relatively large size of the sensor areas, in practice they should be able to pick up some structure with contrast. Artificial patterns, as used on some focus charts, could be problematic but most real world targets should not.
Anyhow, a lot of speculation (as you also acknowledge) based on a marketing diagram which may or may not reflect the actual design. The AF areas are a lot larger than they are marked in the marketing illustration, for example.