Is this a kind of long frame with 3 apertures (left and right ones with lenses in them, middle one empty)? Are there 2 short levers projecting from the front? If so, this is probably the attachment for a close-focusing (or "dual range") Summicron, to which it would attach by a dovetail fitting to enable focusing between 1 meter and 48cm. It won't work with a normal Summicron!