Some great Nikon lenses go for a lot of money used, and most of them are in great shape. But what if I were to find one that had a little nick on the front element, or a couple of little nicks. How much should that matter optically, and how much less should I expect to pay for it? For instance, suppose the lens were the 70-200mm f/2.8, or the 24-70mm f/2.8, or the 28-70mm f/2.8, or the 17-55mm f/2.8. These lenses, in nice condition, tend to sell in the $1,000-2,000 range. But with a nick or two on the glass, how much would they sell for? I've never been able to find such a lens for sale, and I've checked ebay numerous times; so I don't have a clue. Again, two questions: how much does it matter optically, and how much cheaper should it be? Any feedback would be much appreciated! Thanks!