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I have a 10 inch Dob and will soon be purchasing a Nexstar 8SE and live in the light polluted skies east of Annapolis, MD. The city of Bowie, MD (about 8 or 10 miles away) really lights up the western sky. I am interested in DSO's (esp. nebulae and galaxies). I would like to get a good light pollution filter. Budget is $150 or (ideally) less. I would appreciate any recommendations. This is for observing not photography.

Thanks,
Gordon

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Well, I do like the Lumicon Deep-sky filter ($99), but the Orion Skyglow isn't too bad either. Another possibility would be the Astronomik CLS filter ($75 for the 1.25" model). Remember, these broad-band "Light Pollution" filters may help somewhat but will not completely eliminate the effects of light pollution, so you still want to observe under conditions which are as dark as you can easily get to. For nebulae, you are better off with a narrowband "nebula" filter rather than the broad-bands. Clear skies to you.

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

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How does the Orion Ultrablock compare with these? Also, a friend mentioned H Alpha filters for skies in this area. I'm not familiar with these, either.

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The UltraBlock were rated as about the same as the Lumicon and Thousand Oaks UHC filters. Probably can't go wrong with whom ever you choose to go with. Your 2" EP's will work great.

I can't help on the H Alpha filters.

Clear skies,
Scott

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Antares "Vixen Spec" 105mm f/14.3
Celestron C102HD f/9.8 - GSO 10:1 Crayford
Kasai 80mm f/11.25
Orion 203mm f/4.9 Reflector
Atlas EQ-G Mount/ADM Losmandy Saddle adapter/GPS/GoTo Controller
SkyView Pro Mount - TrueTrack Single Axis Drive
Baader Genuine Orthoscopics 5mm,6mm,7mm,9mm,12.5mm,18mm
TeleVue 2" 2x Powermate

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How does the Orion Ultrablock compare with these? Also, a friend mentioned H Alpha filters for skies in this area. I'm not familiar with these, either.

Not sure if it matters but the eyepieces I have that I like the most are the 2 inch Baader Planetarium Hyperions.

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The Orion Ultrablock is a narrow-band "nebula" filter similar to the Lumicon UHC, Thousand Oaks Type II, DGM Optics NPB, etc. It is designed mainly to enhance only emission nebulae and tends to dim other objects. If you want just a "light pollution" filter useful on all deep-sky objects, you may need to go with a broadband one. The Ultrablock is quite effective on emission nebulae (and is not as expensive as some of the other narrowband filters), so it can be worth having. Clear skies to you.

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

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I checked in to Skyglow broadband and you have the option of purchasing one that either threads into the eyepiece or into the rear cell of an SCT. I'm buying a Nexstar 8SE. I presume this would work with the Nexstar and that by purchasing this type of mount I wouldn't have to swap out the filter every time I swapped out an eyepiece? Any other advantages/disadvantages? Link is: http://www.telescope.com/control/product/~category_id=accessory_sale/~product_id=05658

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I would not recommend the rear-cell filter route. You will eventually want to use your filter in some other optical setup like another scope or in someone's eyepiece, in which case, you are kind of out of luck. Also, you will not want to just keep the filter in the scope at all times, as there are a number of instances where the view will be better without the filter. Changing out a filter from a rear-cell is a bit more involved when you want to do something different than it is when just changing the filter on the front of an eyepiece. I recommend getting a filter which screws onto the eyepiece. It may be a pain at times, but in the long run, it is probably the better way to go. Clear skies to you.

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

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If you have both 2-inch and 1.25 inch eyepieces, I would suggest going with the 2-inch filter, rather than the 1.25-inch.

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H alpha filters are useless with regular visual eyepieces.*

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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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I have it, and to be honest, where it really shines is as a planet filter. It is marginally useful for deep sky viewing as it doesn't absorb alot of light, less than the broadband filters like the "Deep Sky". It does darken the sky background, so it could be useful for some deep sky viewing, but I usually use a narrowband filter on nebulae.

A couple of years ago I submitted this photo to a Cloudy Nights contest (I had no illusions of winning). It was mainly to demonstrate the effects of the M&S filter on the Pleiades that I experimented with shortly before.



I have other comparison images (not animated) using the Moon & Skyglow filter as well as the Celestron LPR filter HERE.

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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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David? I read a thread here at CN recently where someone mentioned that a broadband filter had become saturated after a certain point and became less effective. My thought was that they had interpreted the situation wrong - that the filter still filtered out the specified wavelengths, just that there was other LP involved that it didnt stop, much like your description of moon glow. Are there filters that saturate? Will you comment please?
Steve

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Yes, some broad-band filters do tend to "saturate" to some degree, usually under moderate to severe light pollution levels. The filter does reduce the skyglow level by rejecting some of the wavelengths associated with light pollution, but at some point, that reduction isn't enough to allow an object (especially a continuum emitter like a star cluster or a galaxy) to be easily visible. Light pollution is not only the narrow emission lines of Mercury and Sodium Vapor, but includes a huge range of wavelengths all across the visible spectrum from sources like incandescent lighting, halogen lighting, and the broader "side bands" of emission from High-Pressure (HP) Sodium lighting. If the filter isn't really narrow, much of this light will end up in the passband contaminating the view. With broadband filters, by design, they *must* let through a broad range of wavelengths, only targeting the narrower emission sources which again are not the only source of skyglow. Broad-band filters tend to be most effective at skyglow levels ranging from mild light pollution to a dark sky, but with enough skyglow, the levels of that light getting in the passbands of the filters may become high enough that the object may not be visible. This is the "saturation point". For narrow line emitters like emission nebulae, you *can* use narrow-band and line filters to reject more of this light, so they don't saturate nearly as easily as the broad-band filters. Clear skies to you.

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

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