LP filter

[Beardy30]

Has anyone ever used one of these https://www.firstlightoptics.com/light-pollution-reduction/light-pollution-filter.html

be good to know if any good for that price point 

[PeterStudz]

Yes, I’ve had one for a few years. Doesn’t do anything that I can see for light pollution - I’m in Bortle 7. Although strangely it does bring out granulation and sunspot details when doing solar. 

[Beardy30]

Ok that answers that one ! Thanks I think I’ll go for the Neodymium Moon & Skyglow Filter instead- it was recommended but it so expensive 

Edited February 3 by Beardy30

[Cosmic Geoff]

There are two questions you should ask when looking at a light pollution filter:

1) What kind of light pollution do I have in my area? Sodium or mercury lamps? LEDs? Other?

2) What exactly does this filter do? What wavelengths does it pass? or block? 

If you have a diffraction grating or prism to play with, you can actually see what is being emitted by local lights.

[VNA]

Hello, is there a filter for light pollution from LEDs lighting? (I don't think for this kind of lighting?)

[Beardy30]

Thanks Geoff - just wanted a view on that specific filter 👍🏼

Edited February 3 by Beardy30

[Beardy30]

Just now, VNA said:

Hello, is there a filter for light pollution from LEDs lighting? (I don't think for this kind of lighting?)

Nothing will really stop LED lighting effectively- most will vs sodium yellow lights but LED are too bright - some of course will make it slightly better in terms of overall sky flow but I’m afraid the best solution is to go to a darker sight 

[Elp]

The IDAS D2 and D3 were designed with LED LP in mind. From what I've read about (I've only read regarding imaging), people prefer to use a standard luminence filter and remove LP gradients through software. I've tested mine photographically on the Heart and Soul nebula and it certainly helps separate the emission from background, but the star colours were all an even white/green, no blue or red at all even though the nebula was red. Haven't tested it visually.

[Beardy30]

The IDAS D2 and D3 - for visual use? 

[Elp]

Think they're more for photographic use as are the newer P series ones. If you want visual the only ones I know of worth getting for emission nebula are the older Lumicon UHC, TeleVue Nebustar Type 2 and a DGM NPB.

Don's the man to ask:

https://stargazerslounge.com/topic/408975-whats-your-favourite-visual-filter/?do=findComment&comment=4372176

[Elp]

One for you @Don Pensack?

[Beardy30]

I’m not an AP enthusiast- just visual 

[Elp]

The 3 I've mentioned above are for visual.

[Beardy30]

I would say the Astronomik UHC is the number 1 

[Louis D]

Since FLO doesn't show the bandpass information for that filter, I'll have to assume it's a fairly broad bandpass filter.  In my experience visually, they don't help all that much viewing anything.  I prefer a UHC or near-UHC filter with much narrower bandpasses.  I don't know if they're available in the UK, but I've been impressed with the Svbony UHC for observing nebula.  They're about $30 here in the US and work nearly as well as my 1990s vintage Lumicon UHC filter.  The latter has somewhat narrower bandpasses, but visually, they look quite similar under my Bortle 6/7 skies.  They don't really work as light pollution filters for general observation because such a thing doesn't really exist anymore in the era of LED lighting.  It was simple to filter line emission light pollution in the past when street lights were mostly sodium or mercury vapor, but LED lighting tends to be broadband, so it is nearly impossible to filter out while leaving something for our eyes to see.

Below is a composite of various bandpass filter images I've taken with my spectrascope as well as a rather generic Zhumell Moon & Sky Glow (M&SG) filter.  The M&SG is going to be nearly identical in performance to a Baader Neodymium filter.  See the second image comparing the two made by a CN contributor with a professional spectrometer.  As such, save your money and get a generic M&SG if you want to try one.  They're under £10 direct from China on ebay UK.  You can also stack it with a cheap light yellow filter to cut some of the violet/blue light to make a poor man's Contrast Booster filter.

[Cosmic Geoff]

Passband graph for Astronomik UHC: Astronomik UHC Filter

Passband graph for Baader Neodymium: Baader Neodymium (Moon & Skyglow) Filter (baader-planetarium.com)

[PeterStudz]

Thanks for posting that @Louis D… very interesting.

[Louis D]

I came across the term didymium as relates to neodymium and think it might account for the difference between the Baader Neodymium and generic M&SG filters.  It turns out that didymium is a mixture of neodymium and praseodymium which happen to be right next to each in the period table of elements.  The two elements are almost always found together in nature.  Didymium glass has been in use for years by glass blowers and some blacksmiths to cut down the glow from hot sodium to a bearable level visually.  Neodymium accounts for most of the blocking, but praseodymium accounts for some as well.  It's this cutting of sodium emission lines that accounts for it being a decent light pollution filter when sodium lamps are the dominant LP source.

My supposition is that Baader uses pure neodymium glass while the Chinese made M&SG generic filters use the cheaper didymium glass.  As such, the latter blocks a bit more light thanks to the contribution of praseodymium.  I think didymium is probably cheaper because it takes extra processing steps to separate neodymium from praseodymium.  The neodymium glass has higher overall transmission than the didymium (M&SG) glass, so it would be better for faint DSOs.  However, for making a poor man's Contrast Booster in combination with a cheap yellow filter to use while observing planets, the extra sodium line absorption of didymium (M&SG) filters might actually be advantageous.

It also turns out that photographers have been using didymium filters for photographing fall foliage to make it look more vibrant by cutting some of the orange/yellow part of the visible spectrum to create a band-gap to reduce a certain muddiness to the image.  This is basically what the Contrast Booster is doing, but additionally it cuts violet light with a yellow filtration to further increase perceived contrast visually.

[Ratlet]

Don't have much to contribute of the light pollution filter side of things, but I'm a big proponent of stacking the moon and sky glow filter with a yellow.  I use it all the time when I'm doing planetary and find it helps quite a bit.  I like to call it the Baargain Contrast Booster because it's a fraction of the cost of the baader version.

Edited March 11 by Ratlet