This is the Lomography Diana Splitzer. It's used for taking photos that are split. It's in excellent condition as it's almost unused, but please be aware that it's over 10 years old, so there may be some material degradation. The box has some damage. Detailed instructions are provided in the middle of this page on the official website: ↓ https://filmphotography.eu/t/ja/diana-f/ How to use it is described here: ↓ https://www.lomography.com/about/faq/1426-how-do-i-mount-the-diana-splitzer-onto-my-diana-f-camera