The Orion Hydrogen-Beta Filter may be the only way to see the faint and elusive Horsehead, California, and Cocoon Nebulas. It blocks everything but the hydrogen-beta light these faint nebulas emit, providing the contrast needed for viewing. By isolating the hydrogen-beta spectral line centered at 486.1 nm in a 12nm band-pass and blocking other wavelengths, it effectively blackens the background sky, allowing the faint nebula to become clearly defined. It increases contrast even under dark skies so you can visually capture these prized targets. Use with a moderate to large aperture telescope under clear, dark viewing conditions. Threaded to fit 1.25" eyepieces and diagonals.