FYI

http://www.sigma-photo.com/lenses/lenses_tele.asp
ｄｕｎ　ｋｎｏｗ　ｗｈｙ　sigma 105 F2.8 macro is not in the list , maybe not 100% compatible ?

haven on my mind

-easy to register , free
-all participants is going to a place to take photo , really depends on your creativity on that day(s) only , fair for everyone
-paul , interested ?