Yashica Yashikor Aux 55mm 1:4 Wide Angle and Telephoto Converters -Clean-
These are super cool lens converters that you screw onto the front of a lens with 55mm filter threading. You should look up some example photos from these, I think that you'll be impressed, the images are very sharp. These would be a great way to change up your focal length without carrying around all of your lenses.
These ones are in excellent condition with clean glass. They come in the branded leather case.