Optical glass lens;aluminum frame;significantly reduces light pollution;great for city and suburban observation. for Sky background is darker;and contrast of emission nebulae are noticeably improved;the perfect filter for viewing nebula from light polluted skies for boosting the contrast of nebula from dark for sky 1.25'' diameter simply attach to eyepiece cased in a sturdy transparent for case;standard filter thread for 1.25" eyepieces and other accessories. Due to its ability to produce exceptionally for and clear images;this UHC filter is considered one of the most popular astronomy accessories;it can be used not only for observations but also for astrophotography. UHC filters light pollution reduction filters are designed to selectively reduce the transmission of certain wavelengths of light;especially those produced by artificial light.