This adapter is made to fit the large 6x7cm format field flatteners from Astro Physics and TEC. These flatteners have a rear collar that clamps various adapters to the back of the flattener. Unfortunatley this makes adaption to your camera somewhat difficult. This adapter resolves that problem by converting the back of the flattener to a standard M68 thread. It is then a simple case of adding standard adapters to the flattener to acheive the correct back focus and adaption for your camera.