Crystalview Moon and Skyglow Filter improves the blocking of mercury-vapor light and higher transmissions, at the critical hydrogen-alpha and hydrogen-beta lines. Bright, light-polluted skies are made to appear darker, and the contrast between the object viewed and sky is improved significantly. The Moon and Skyglow Filter allows maximum transmission of the important wavelengths of hydrogen-alpha, hydrogen-beta, and doubly-ionized oxygen most commonly emitted by nebulae. Views of galaxies and star clusters are also slightly enhanced. This filter is designed to be attached to 1.25″ barreled eyepieces.