I have a Nikon 200 f4 micro AF that I enjoy using very much. I love the way it can isolate the subject form the background much better than my 90, and also the tremendously smooth out of focus transition it produces. However there are a couple things I don’t really care for. One is the physical length of the lens (7.7”). Also, it would be nice to have an f2.8 lens for a brighter focus area when lighting isn't the best. The Sigma 150 2.8 has gotten some very high praise from several respected people. It is only 5.4” long and about 10 oz lighter than the Nikon. It also has a removable tripod collar. I was wondering if anyone has compared the two for image quality, bokeh and handling. I have someone interested in buying my Nikon but I don’t want to get rid of it and be sorry. The $$ difference is nice but certainly not a reason to sell.