I have somewhat of a mystery Summicron 50mm f2. The serial number is 2295439, it has 10 blades in the aperture and no little red dot or blob on the side of the lens. I've searched the web, looked it up on Ken Rockwells site and can't find any info. Any info on value and use would be appreciated. It's on an M6, shot a couple of rolls through it and really like the results.