(nikon mount) Alright, so I shoot a D50 and I have the (craptacular) kit lens. I was tossing around getting the 50mm 1.8, but was thinking that I might be better off ponying up the extra $400 or so and getting either 18-50mm 2.8 or a 24-70mm 2.8 (both Sigmas). Any opinions on this? I realize the bigger aperture would be nice, but I'm thinking it would be of a greater benefit to have a focal range to work with as opposed to a fixed focal length. I hate the kit lens I have now, so I'm thinking this will completely replace it. Not so the case with the 50mm 1.8. Any advice or opinions would be great. Thanks!