F 0.5 Focal Reducer/Field Flattener 1.25" for Starshoot Imaging Cameras - with Standand Filter Threads Reduces your telescope's focal ratio by 0.5, which results in a wider field of view. It increases imaging area and allows capture of larger starfields or deep-sky objects, works as essentially a reverse barlow. Two-element optical lens helps transmit more light, nice green sheen when held at an angle. The reducer has standard 1.25inch telescope threads M28.5x0.6 and fits onto the nose of any 1.25 inch eyepiece, diagonal, extender tube, or camera adaptor fitting that format. Threaded male on one end and female on the other so it can both have a filter attached and be threaded onto an eyepiece or camera. Nice anodized aluminum housing