Neutral density filters are excellent filters to reduce the overall brightness of an image to cut down glare while viewing bright astronomical objects through a telescope. They are useful for splitting binary systems, comfortably observing the moon, or stacking with other planetary filters. ND filters retain true color balance of the objects being observed since all wavelengths are transmitted uniformly over the entire spectrum. Astromania 2" 90-degree 99% Enhanced Dielectric Diagonal Mirror uses multi-layered dielectric coatings in order to guarantee a maximum reflection of 99% with the highest contrast and optimal sharpness.The residual stress in the plane mirror which can occur with the dielectric vapour deposition process is ruled out here. This slip fit 2-inch diagonal with 1.25-inch adapter, plus the Schmidt Cassegrain thread to 2-inch accessory adapter and other Schmidt Cassegrain rear thread screw-on systems, is compatible with both slip-fit and screw-on mounting systems. The optics are made with Pyrex glass and comes with dielectric coatings for the most light transmission possible. Beside eyepieces, a star diagonal is one of the most important accessories. What is the use of a good objective or the best eyepiece if the star diagonal is inferior? We recommend the Astromania 2" 90-degree 99% Enhanced Dielectric Diagonal Mirror to everyone, including those working with high end instruments. The star diagonal permits full illumination of 2” wide field eyepieces.