The Blocking Filter is the second element in any Coronado H-Alpha system, it is just as crucial to your safety and the system''''s'' performance as the front element. If you are switching to a longer focal length telescope your SolarMax system you can purchase blocking filters separately. The BF-10 to be used on telescopes with a focal length <1000mm. The Blocking Filter is not a stand alone filter. It is an integral part of the Coronado design and cannot be used without a SolarMax series filter on the front of the optical system.