By the way, if you want non-telescope-contaminated info, XW field curvature plots, showing deviation of focal surface from an ideal focal plane, here:
http://www.pentax.co.jp/japan/tech/xo-xw/64.html
And in case you're interested in transmission vs wavelength, it's here:
http://www.pentax.co.jp/japan/tech/xo-xw/63.html
The amount of technical data Pentax discloses about their EPs is impressive.