Yep, I saw an early 1990s Canon EF 600mm f/4 at my local store's used cabinet - attractive price, but I didn't bother getting them to show it to me because ... 13.5 pounds. OK for tripod use in a limited set of locations, not too great for hauling around after wildlife / birds. I have been hoping to see a 600 DO, but I anticipate a price in the $16K to $18K range. Gulp. Rentable, I suppose.