Coronado 15mm Blocking Filter (BF15ST)

Coronado BF-15 (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. Use the following guidelines for selecting which blocking filter you need for full illumination of the Solar disk based on the focal length of the telescope being used: focal length.