This reducer/flattener is compatible for SkyWatcher 72 ED refractors (diameter 72mm and 420mm focal length), it has a female thread on the telescope side that allows the user to screw it directly on the focuser and ensuring a strong mounting and a correct optical alignment. On camera side it has a M48 thread that allows to install any accessory, DSLR or CCD camera with the appropriate adaptors or extensions tubes. Ideal for sensors and CCD with a maximum size of 24mm x 16mm (APS-C), for its correct use the working distance between the reducer thread and camera sensor must be 55mm.