Baader Neodymium Moon and Skyglow Filter
Posted 17 December 2009 - 02:37 PM
Narrow-band interference filters have been around for many years now. Nebula filters, “deep sky” filters, “Ultra-high contrast” filters, etc. All designed to enhance the viewing of emission nebulae by blocking specific wavelengths of artificial light sources, but letting the wavelengths of the viewed objects to pass through.
Personally, I’ve never cared much for them, as they all decrease overall brightness – some quite substantially – of the object in view, despite the fact that they DO increase contrast. Don’t get me wrong. I use an h-beta filter to view things like the Helix nebula and such. From my location, these objects would be invisible without one, but whenever possible I try to observe without a filter.
With emission nebulae, the transmission of most narrow-band and line filters at the wavelengths of the nebular emission lines have transmissions greater than 90%. The human eye is basically incapable of detecting a brightness difference much smaller than 10%, so in fact, for nebulae, these filters do not detectably decrease the overall brightness of the nebula. They will, of course, impact the brightness of stars but when one uses a nebula filter, one does not care about stars all that much. Narrow-band and line filters also have never been recommended for anything other than nebulae, so using them on other objects is not good practice. Most experienced deep-sky observers use nebula filters extensively, as they can drastically increase the contrast over something like the Moon and Skyglow filter without reducing the nebular brightness significantly. Also, if the author uses the H-Beta filter on the Helix (NGC 7293), I am not surprised that it dims it. The Helix has rather weak H-Beta emission, so the H-Beta will nearly kill it (it is best in a narrowband filter or an Oxygen III line filter). Filters also must be used in the proper magnification range, and with an eye that is fully dark-adapted with proper use of averted vision. Without these steps, many of the substantial benefits of interference nebula filters will not be seen.
The article also says:
The The Baader Neodymium Moon and Skyglow filter is different. Unlike other filters that have a few transmission peaks for one or two specific wavelengths, this filter has a very complex transmission profile that allows much more light to pass through from a wider variety of objects, including stars, planets, and galaxies.
The Baader Moon and Skyglow is a broadband filter not a lot different from many other filters like the Lumicon Deep-sky, Orion Skyglow, Astronomik CLS, Thousand Oaks LP-1, etc. Broadband filters *do* help a variety of deep-sky objects, although they do not provide the same level of contrast boost on nebulae that the narrower Narrow-band and Line filters do. Comparing a broadband filter with the single or multiple line filter is totally unfair, as they were designed for different applications.
Like it’s name suggests, this filter also helps the view of deep-sky objects in moonlight, something that other filters don’t do. The effect is slight, but there.
Again, many other filters will provide a boost in contrast under moon-lit conditions, especially the narrow-band and line filters when used on nebulae. The Orion Skyglow (a broad-band filter) which I just reviewed pepped-up things a bit under the nearly full moon, although for emission nebulae, the narrower UHC or OIII filters tended to do a little better. One has to take precautions to keep from losing dark adaptation under moonlight, which is one reason many people fail to see much benefit from these filters.
Again, it is best to understand the proper use of the various filter types, and compare filters to others of similar type rather than to narrower Nebula filters. Clear skies to you.