The following is an excerpt from the internet: Close-up attachment for Leica M-series cameras. The product codes are SOOKY-M or SOMKY, later 16507. This accessory allows close-up photography from approximately 1m to 0.5m when used with a collapsible Summicron 50mm f2 or Elmar 50mm f2.8. When attaching a fixed-barrel Summicron, the lens head must be removed and the UOORF/16508 adapter is used. It was originally released for the Leica M3, but can also be used with current digital Leica M-series cameras. When attaching the lens, firmly push in the collapsible section while rotating it clockwise to secure it. This is an accessory that close-up enthusiasts should try at least once. There is some clouding or scratching on the viewfinder glass, but visibility is not affected. It's a rare item, so please consider it.