The Solarmax series filters come in two parts, the front narrowband element (sold separately) and a secondary interference filter which mounts at the eyepiece end of the telescope. You cannot use the individual units separately. If you do not have a SM40, 60, or 90 or a T-Max tuner, it will be more economical to purchase them as a package. Otherwise, choose the secondary blocking filter based on the focal length of your telescope.