This 1.25'' Moon filter made of attenuating glass with plane-parallel faces is simply screwed into the eyepiece thread. It reduces the Moon's level of brightness and thus increases the contrast during observation. This filter is mainly required during larger Moon phases, because at those times the glare of the Moon is at a maximum and tends to become uncomfortable rather quickly.
We measured 30% light transmission (corresponding to optical density ND05), which means the filter is perfectly appropriate for telescopes with rather small diameters. For larger telescopes, i.e. 200 mm and more, a filter with less transmission (eg. 8%) would be more effective. In this case, we would recommend, for instance, the Lumicon ND13 grey filter.A maximum of flexibility is achieved with a variable polarizing filter .
