Originally posted by twitch Good point. Perhaps the DA21 is a better exmaple.
Well, in the case of the 21 vs 31, I'd probably cite the fact that there is an inflated market for the MIJ copies of the 31 (which on average sell for $100-200 more than the AIV copies, at least here in the US). Now, I'm taking a position on whether or not that is justified (or right), but that is the reality of the used market right now. So the more fair comparison is the price of a new (AIV) 31 vs the price of a used (AIV) 31 as compared to the price difference between the new and used 21. In this case, the markdown for a used copy is about the same (~20% off in each instance).
But I do agree with and understand your original point. And I certainly feel that (for the most part), the prices of lenses on the used market are neither over nor under-priced. They are the prices that people are willing to pay for the lens, hence they are exactly "right". They might be more than a similar Nikon or Canon lens, but we're not talking about apples and apples in most cases. A lens that is truly over-priced, whether new or used, simply won't sell well and the price is usually adjusted accordingly.