This is a Kowa anamorphic lens. It has a screw thread of 50mm, and I used a step-down ring to make it 52mm to attach it to a Nikon lens and have fun with it. This lens is used to compress the horizontal width when shooting. It's a special lens, so I would appreciate it if you could look up the details. The fifth photo is an example of the compressed photo expanded; sorry for the poor image quality. I believe the lens I used was a Nikon 55mm f/1.2. No returns or exchanges, please.