LP-4 H-Beta Line Band Filter

The Thousand Oaks LP-4 H-Beta Line Band Filter is a specialized narrowband eyepiece filter designed for visual observation of extremely faint emission nebulae. With an ultra-narrow 12 Ångstrom passband centered on the hydrogen-beta emission line, this filter isolates light at 4861Å and dramatically improves contrast for viewing challenging objects like the Horsehead, California, and Cocoon Nebulae. The filter's steep transmission cutoff slopes block light pollution and natural sky airglow, creating a dark background that reveals nebular detail otherwise invisible from most observing sites. Optimized exclusively for visual use, this filter requires a large aperture telescope (10-12 inches or larger) and long focal-length eyepieces for best results, making it an essential tool for serious deep-sky observers pursuing these elusive "observing trophy" objects.