SkyGlow filter with a 1.25 inch diameter of high quality. Greatly improves the contrast in lunar - planetary observations, while reducing the so-called light pollution (ie the glow effect in urban and suburban areas). It has a thread on both sides of the luminaire.
Connection of ALL astronomical filters with the exception of solar film filters (which are filters for the lens) is accomplished by screwing the filter into the frame of the eyepiece from the opposite side than applying the eye (ie from the side that we put in the eyepiece extractor) . The filters can be additionally connected with each other, because they have threads on both sides of the luminaire.