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Has anyone ever tried the Baader Planetarium Moon and Skyglow filter? Here's what the seller says about it: "The Baader Planetarium Moon & Skyglow (Neodymium) filter brings an entirely unique approach to contrast enhancement and light pollution reduction. Based on earlier research at Carl Zeiss, Baader has developed a new filter that uses Neodymium glass which filters out a few specific wavelengths from streetlights as well as skyglow from the Moon. The unique spectral characteristics of Neodymium also boost color contrasts by isolating the Red, Green, and Blue regions (so-called RGB enhancement). The result is a filter that leaves natural colors intact, but enhanced."

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Well, quite frankly, this looks like a little too much dealer "hype". First, from the filter's transmission curve, the unit can reject the light pollution lines of Mercury Vapor fairly easily, but lets through much of the broad band of HP Sodium Vapor emission (roughly from 5400 to 6400 Angstroms). There is more and more city lighting which is being based on HP Sodium lighting, so the filter would not perform quite as well on rejecting that form of skyglow as a filter with a single broad "notch" like the Lumicon Deep-sky filter or the Astronomik CLS filter.

Second, moonlight is basically reflected sunlight over the entire visual spectrum, so there is no way any broad-band filter can effectively filter it out to allow deep-sky objects to be better seen. It may help *for* viewing the moon, but not for rejecting the scattered moonlight that is the bane of deep-sky observers. Clear skies to you.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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