Here is an excellent article by Mr. Peter Zheng, very informative:-
http://forum.xitek.com/showthread.php?threadid=655516
(Text in Simplified Chinese, another reposted full version in Traditional Chinese can be found Here)
The article contains all the essential details for the patents and optical designs used by various new Pentax digital lens models, namely, DA* 16-50, DA* 50-135, DA 10-17, DA 35 Macro, DFA 50 Macro. In fact, Tokina has never had any patent of any lens design at all! Yes, nothing. So, what was that old Pentax-Tokina lens "co-development" actually about??
Peter, Well Done! Bravo and My Thumb Up! Please do continue to keep up the good works in the future!