Made of good quality aluminum alloy, strong, durable and wear-resistant and corrosion resistant. Compact size, lightweight and portable. Have an obvious effect to eliminate harmful city light. Using an international standard talking wire, suitable for a variety of astronomical telescopes with the British standard wire thread. Align the filter thread to the rear thread of the eyepiece, rotate the filter lens into the eyepiece, then observe and use. Using nanometer coating system to ensure that the film layer is resistant to high temperatures, corrosion, not easy to fall off and other characteristics of uniform coating.