It’s a Tele Converter Lens a friend of mine turned me on to that changes the focal length of my Shorty’s (Fujifilm X100) 20mm, to a 50mm lens. The magnification is 1.4X without much chromatic aberrations, but does produce pincushion distortion. With a good image editor, you can easily correct those anomalies.
In this instance, I took it out at night around the neighborhood. The added weight helped in balancing the camera and made it easier to shore up when snapping at long shutter times. Plus, I had a little fun with filters, too.