This week I enabled myself with a cheap Sigma A 5,6-400 mm and mounted the lens together with a Takumar-A 2x TC on my istD.
http://360.leende.net/sigma400 Hope you like it. Not the greatest pictures and the lens could be better, but I enjoyed the wildlife. The Sigma works like any Pentax-A lens on the istD, combined with the Takumar-A 2x it only works in manual green button mode. Toine
