Coronado BF30, 30mm 2" Staight Tube H-ALPHA Secondary Blocking Filter for Solar Viewing - for SolarMax, 60, 90 & 140 Solar Filters & Telescopes with Focal Lengths of up to 3000mm

Coronado BF-30 (straight through) type secondary blocking filter. 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. Cannot be used without an SM front cell.

Secondary interference filter for full disc image of the Sun for telescopes up to 3,000mm focal length, with precision machined 2" barrel diameter. Requires 2" focuser.