I got this very odd mystery lens accessory, with nothing to identify it at all. It says "Germany, " but otherwise says nothing. It has a male 58 mm. thread on the side not shown. The entire assembly rotates, and also the half-sector inside it rotates separately. One half the device is permanently closed, except for a half-circle open in very middle. The little swinging door covers a small hole off center in the part that rotates, and the door has a sharpened edge where it aligns with the edge of the rotating sector. It looks as if it might be some kind of focusing aid for astro photography, but I have found nothing so far. The swinging door covers a diamond shaped hole, but that hole is never fully open, and only meant to allow the hole in the door to show through without requiring precision. It is not possible to have both the center hole and the off center hole open at the same time, which would seem odd if it's an astro focusing device. I hope I've explained it enough. Any clues about what this strange device is? The part that goes on the lens is aluminum, and the rest plastic. There is no room for anything inside it, and no apparent way to attach anything else to it. I got it from a used camera dealer who knows a lot, but also does not know what it is.