Coronado 15mm Blocking Filter (Straight Through) for Telescopes = 1500mm

The BF-15ST Blocking Filter from Coronado is the secondary interference filter in a Coronado H-Alpha solar viewing system. Blocking filters are not stand-alone devices; they must be used in conjunction with a SolarMax filter. In a solar viewing system, the blocking filter is just as crucial to the viewer's safety and the system's performance as the front element. This 15 mm blocking filter, the BF-15ST, features a 1.25" straight-through design and it's intended for use with telescopes that have a focal length equal to or less than 1500 mm.