I purchased this lens a few months ago and because it is not that fast, I have use it mostly outdoors. I just can't figure out why the pictures I shoot seem "soft". I tried stopping down (?) -- never sure when they say stop down whether it refers to the numbers decreasing or the actual aperature decreasing . . . anyway I stopped down to 7.5 (since they say stop down two f stops from the widest aperature to sharpen but still not that hot. Any clues? I shoot A mode on my D80. Is this just this lens. It is sharper at 24 . . .