This is a very special lens matched to the 100/2.8APO . It allows the 100/2.8 to be focused down to 1:1 . If you have a 100/2.8 (see separate listing) this is a very nice accessory in essentially new condition. Can t find a mark on it anywhere .
Priced to sell at less than what they have been going for on eBay. $500 net to me.