Okay we all know for canon lenses there is the "L" series with the red ring. Well they of course are very expensive and I recently got a 50mm F/1.4 and its sharpness is amazing. Im sure the 50mm F/1.2L is even more sharp. Anyways, is there a way to look for a lens that is not a poor quality lens (such as kit lens 18-55mm F/3.5-5.6) but also not a pro quality? It seems lots of decent lenses that are not L lenses, are USM. Is it okay to assume most lenses that are USM are somewhat decent in image quality?