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