Hi, am considering this lens for my mamiya 645 super. Could any one who have this lens give some comment/advices: a) is this hand-holdable or must be using either the monopod or tripod for photo taking? b) is F/5.6 capable of getting some good "bokeh" effect? Any images sample will be greatly appreciated. c) what does the ULD stands for? Are there different versions of this lens other than AF one? d) as compared to the 200mm APO lens (the price is much higher), which one will you guys recommend? Other than the focal length different, is this justified for the high price? Currently am using the 45mm f/2.8, 80mm f/2.8, 150mm lens f/3.5 As usual, thanks for all the comments/feeback.