The ever most expensive Pentax DA lens has been reviewed in full by the PF:-
http://www.pentaxforums.com/reviews/pentax-da-560mm-f56-ed-aw/introduction.html
I have gone though the IQ parts of the review. From the test pictures and samples posted, I found that the resolution of the lens is low, flare control of it is so-so, CA of it could be obvious, bokeh of it is not that pleasing, i.e., rough and without good feel of separation which is just odd enough..
Although the PF editor writes and comments in words that the lens is performing good for each of the above departments, I would rather opt to inspect the posted pictures instead as one picture is worth more than one thousand words!
Anyway, you may agree or disagree what I have concluded. So you should decide yourself for what I have blogged. Just go read through the PF review and measurebate things yourself! Yes, I do promote their website this time! ;-D
Related:-
Mounting a (Cheap) Telescope onto a Pentax (K-mount) Camera Body