In the need for a wide angle for my FF. Would like to stay with 77mm filter ring size for landscape. Or mabe a link to stepdown rings for lee holder. 2.8 is needed for low light/dark with this noisy 5D2! Really getting into startrails. My 10-22 is nice on the 7D but a no go on the FF and would like to keep the 24-105.The 8-15 Fisheye is just too wide for stars. Must be sharp as i am a very hard on pixels! Tamron or Sigma is not out of the question.