I am looking for suggestions for a good "walk around" lens for my d5100. I currently have a Tamron 17-50mm that I initially loved, but I can't quite determine if the image quality is really bad because of that lens or my camera. If it turns out to be the lens, can anyone give me a good all purpose lens that would be similar? Nikon makes a 17-55 f2.8 I can get new for $1300. Was hoping for something less than $1000. Found a used for $830 through B&H. Any experience on buying used lenses? That makes me a little nervous as well. If I am having image quality issues, can anyone educate me on whether it would be primarily the camera or the lens that would be causing it? I am getting very frustrated. I have the Nikkor 50mm and 85mm, and they seem to be ok, for the most part, but are still sometimes hit or miss. Thanks!