John,

Nothing to add to these two excellent discussions regarding imperfections on the glass. This note is just to add that it is very possible to pick up outstanding examples of used lenses for great prices. Two of my lenses, a 125mm Fujinon and a 450mm Nikkor M were purchased at extremely low prices compared to the "normal" used prices for those lenses. The glass, barrels, and shutters on both of them look like new. The price for the Nikkor M was so low (compared to other 450mm Fujinons or Nikons) that I could not pass it up, even though I was looking for a Fujinon! If you keep looking, you can usually find a lens for a good price that is in excellent condition. My other lenses have a few imperfections, but none of them are on the glass. If the glass is marked, I take a pass on the lens.