I've been shooting with a 90mm and have found myself trying to compose much too close. I think what I need is a longer lens but I have nothing to base a purchase on. I'm very interested in portrait work and kind of like the idea of the 150mm with diffusing discs but then what about the 180mm? I guess what I'm asking is who shoots with these lenses and what do you like and dislike about them? Thanks in advance, Alan.