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Old 20-06-2021, 08:33 PM
Hans Tucker (Hans)
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LPR (Light Pollution Reduction) filters

Advertisements for LPR (Light Pollution Reduction) filters claim they can drastically reduce the effects of light pollution. Block artificial light from Mercury Vapour Lamps and Sodium Vapour Lamps.

Do they have an effect, if any, in reducing the effects from street LED lights?
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Old 20-06-2021, 11:39 PM
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Originally Posted by Hans Tucker View Post
Advertisements for LPR (Light Pollution Reduction) filters claim they can drastically reduce the effects of light pollution. Block artificial light from Mercury Vapour Lamps and Sodium Vapour Lamps.

Do they have an effect, if any, in reducing the effects from street LED lights?
Alas, city lighting has become more broadband. Here in Los Angeles, someone recently measured around 130 different wavelengths of sky brightness from light pollution, covering the entire spectrum.
The use of broadband filters as "light pollution reduction" filters has pretty much come to an end in modern municipalities where LED lighting is common.
Today, we have the headlights on cars, incandescent lighting, fluorescent lighting, LCD lighting, LED lighting, arc lights, neon, argon, krypton, and xenon lighting, sodium vapor, mercury vapor, halogen lighting, and too many other sources to list.

Worse, a filter that removes only some of the light pollution wavelengths and passes the rest will often have internal reflections between layers of coatings that scatter MORE light than the use of no filter at all.

However, for emission nebulae in particular, which emit light basically at 3 closely-grouped wavelengths, the use of a narrowband (not a broadband or LPR) filter will help a lot. The filter will suppress nearly all of the light pollution wavelengths, improving the view of emission nebulae.
Unfortunately, these filters will not help the visibility of stars or galaxies, or reflection nebulae, or dark nebulae, etc.

In today's urban environments, the best way to view most deep sky objects is to travel to darker skies.

Still, for star clusters (open and globular), or double stars or carbon stars, you can simply increase the magnification to make them more visible. As you bump the power up, the background sky in the eyepiece dims, but the stars do not. Here in LA, I can barely tell the bright star cluster M11 is there when I look at it with 50x. At 150x, though, the cluster has become populated with lots of faint stars, and at 200x, the view is similar to what I see in dark skies.
So at least for any object containing stars, increasing the magnification will help.

Galaxies, however, emit light across the spectrum, and because they are extended objects, increasing the magnification also dims them. Other than super-bright galaxies like M104, seeing them really requires darker skies than a city environment.

Ironically, dark skies is the environment where the broadband ("LPR") filters work best--by turning up the contrast a tiny bit.
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Old 21-06-2021, 01:11 PM
Hans Tucker (Hans)
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Originally Posted by Don Pensack View Post
Alas, city lighting has become more broadband. Here in Los Angeles, someone recently measured around 130 different wavelengths of sky brightness from light pollution, covering the entire spectrum.
The use of broadband filters as "light pollution reduction" filters has pretty much come to an end in modern municipalities where LED lighting is common.
Today, we have the headlights on cars, incandescent lighting, fluorescent lighting, LCD lighting, LED lighting, arc lights, neon, argon, krypton, and xenon lighting, sodium vapor, mercury vapor, halogen lighting, and too many other sources to list.

Worse, a filter that removes only some of the light pollution wavelengths and passes the rest will often have internal reflections between layers of coatings that scatter MORE light than the use of no filter at all.

However, for emission nebulae in particular, which emit light basically at 3 closely-grouped wavelengths, the use of a narrowband (not a broadband or LPR) filter will help a lot. The filter will suppress nearly all of the light pollution wavelengths, improving the view of emission nebulae.
Unfortunately, these filters will not help the visibility of stars or galaxies, or reflection nebulae, or dark nebulae, etc.

In today's urban environments, the best way to view most deep sky objects is to travel to darker skies.

Still, for star clusters (open and globular), or double stars or carbon stars, you can simply increase the magnification to make them more visible. As you bump the power up, the background sky in the eyepiece dims, but the stars do not. Here in LA, I can barely tell the bright star cluster M11 is there when I look at it with 50x. At 150x, though, the cluster has become populated with lots of faint stars, and at 200x, the view is similar to what I see in dark skies.
So at least for any object containing stars, increasing the magnification will help.

Galaxies, however, emit light across the spectrum, and because they are extended objects, increasing the magnification also dims them. Other than super-bright galaxies like M104, seeing them really requires darker skies than a city environment.

Ironically, dark skies is the environment where the broadband ("LPR") filters work best--by turning up the contrast a tiny bit.
Thanks Don. Oh to be 10 again when street lights went out at 12am and I could see the LMC and SMC from suburbia. Maybe it is time to utilize the ASV membership and head for darker skies.
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Old 25-06-2021, 03:00 AM
Renato1 (Renato)
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The LPR filters are never as amazing in light polluted places as the ads make out. My set are over ten years old, but the ads were the same back then. My observations from using them in an 8" SCT follow.

In Broad-band filters, there are broad Broad-band filters and narrow Broad-band filters. The Lumicon Dark Sky filter was broad Broad-band filter which I found pretty hopeless in my polluted sky, but actually very pleasant at a darkish sky. In sharp contrast was my Celestron LPR filter, which was narrow Broad-band filter, and was a fair way towards being a an Ultra High Contrast (UHC) filter, and worked pretty well on emission nebula and many planetary nebula in a light polluted sky. In between the Lumicon and Celestron was the Orion Skyglow, which didn't work as well as the Celestron one, but didn't kill off the stars as much leading to a more pleasant view.

When I got my Narrow-band filters - the Lumicon UHC and Orion Ultra Block - I didn't like them much. They killed off too many stars, and anyway, were redundant as I'd also bought an Oxygen 111 filter - which killed off more stars, but showed more detail in emission nebula and enabled one to see the big planetary nebulas and spot the tiny invisible ones - by having them appear and disappear while either passing the filter between the eyepiece and eye, or just tilting the filter 45 degrees while aiming at where the invisible planetary nebula was supposed to be (known as "blinking"). All three of these filters worked pretty well on emission and planetary nebulas in my light polluted sky.

But as time went on, I suddenly decided I liked the UHC filters more tha the O111, as the view of emission nebulas was more aesthetically pleasing. The 0111 filter was relegated to the task of finding the 15 to 20% of planetary nebulas that the UHC filters wouldn't show up.

However, before my back went and I could still set up my 14.5" dob, the O111 filter got a lot more use in it, since the stars weren't dimmed as much as in the 8" telescope.

And one day, out of idle curiosity, I bought a Kson UHC filter - and in my 5" Mak it gave better detailed and more aesthetically pleasing, views to my eye of emission nebulas in Scorpius, than the other two Narrow-band filters.

So to sum up, yes, some filters are useful under light polluted skies if you have a strong interest in emission nebulas and planetary nebulas, but they aren't of much or any use for reflection nebulas, open clusters, globular clusters and galaxies. And their characteristics, mean that there will be differences in how people perceive an rate them in the degree that they dim down surrounding stars and enhance the nebula, as well as the way they perform in different sized telescopes.

Now - the most important point. If you have a backyard surrounded by houses with lots of lights coming through blinds and the occasional street light as well, just attaching whichever LPR filter you have to an eyepiece is going to result in you're being disappointed. You have to block off stray light coming into the side of your eye.

In my case, depending on where I was positioned to see some object,
a. sometimes being next to a fence or pole would suffice to get a good view, or
b. sometimes a butterfly eyepiece cup would suffice to get a good view, or
b. sometimes that butterfly cup, together with one or two hands cupped around the eyepiece would give me a good view, or
c. sometimes, especially when doing blinking to see an invisible or very dim planetary nebula, I needed to put an opaque piece of black cloth over my head and the eyepiece to stop the stray light. And in cold weather, this only works for a short amount of time, until you start fogging up the eyepiece and filter used for blinking.

Good luck with whatever choice you make.
Regards,
Renato

Last edited by Renato1; 25-06-2021 at 03:10 AM.
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Old 25-06-2021, 04:15 AM
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Narrowing the bandwidth of a filter increases contrast by darkening the sky without darkening the nebula.

So the narrowest filter that passes the necessary spectral emission lines will be best for contrast.

Nebulae emit light at about 3 spectral wavelengths we can see well:

H-▀ at 486nm (blue)

O-III at 496nm (blue green)

O-III at 501nm.(blue green)

So, if the nebula emits light at all 3 wavelengths, we want a filter that passes all 3 wavelengths, like a narrowband filter (Lumicon UHC, DGM NPB, Astronomik UHC, TeleVue Nebustar II, Orion Ultrablock).

That would include the large hydrogen gas clouds like M8, M20, M17, M16, M42/43, North America, etc.

If the nebula emits only the O-III light, then a narrower filter that passes only the O-III lines will improve contrast.

That would include planetary nebulae, Wolf-Rayet excitation nebulae (Crescent, Thor's Helmet, etc.), and supernova remnants (Veil, etc.)

If the large faint nebula emits only H-▀ light, then a narrow filter passing only the H-▀ light is best.

That would include the California Nebula, IC434 behind the Horsehead, and a lot of the Sharpless Nebulae.



Bear in mind, though, that a narrowband passes all those wavelengths, but it's bandwidth is a bit wider than optimum for just an O-III emitting object.

Hence, it's useful to have an O-III filter. The H-▀ filter is only good for a few objects, so it's WAY down the list of filters to buy.



In the spectrum, O-III emission is at 501nm (strong), 496nm (1/3 as strong) and 493nm (1/100 as strong).

We need as much help as we can get visually, so we ignore the 493nm line and make filters for visual use that pass the 501nm and 496nm lines, like the O-III filters that pass both bands.

Photographically, we can narrow the bandwidth to just the 501nm line and make our exposure longer, so we can make the bandwidth narrower for higher contrast.

Visually, though, the photographic O-III filters (Baader is one) are dark and filter out 25% of the light from the nebula, making the nebula dimmer.

So for visual use, you want 2 O-III lines to come through, and for photography only 1.

Most visual O-III filters of 12-16nm bandwidth pass 2 O-III lines, so can be fantastic visual filters.
I would stay away from the 1-line O-III filters (3 to 10nm) for visual use
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Old 26-06-2021, 10:23 PM
Hemi
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That’s fantastic Don,

Cheers
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Old 08-07-2021, 11:02 AM
mandragara (Richard)
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To my eyes things look slightly, and I mean slightly, better through my Baader Neodymium filter than unfiltered from a Bortle 6 area. We are talking maybe a 5-10% relative enhancement though.

My Astronomik O-III on the other hand is really a stellar filter for me. With my 30mm 82deg eyepiece is produces some killer views of Carina etc.
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Old 08-07-2021, 12:35 PM
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To my eyes things look slightly, and I mean slightly, better through my Baader Neodymium filter than unfiltered from a Bortle 6 area. We are talking maybe a 5-10% relative enhancement though.

My Astronomik O-III on the other hand is really a stellar filter for me. With my 30mm 82deg eyepiece is produces some killer views of Carina etc.
Hi Richard & Hans,

Here is a comparison I did a few years back in Bortle 6 Brighton (SQM =19.14 & 2370 Ácd/m^2) of a couple of similar broadband didmyium type photographic filters (Hoya Intensifier V Marumi redhancer V no filter) with nearby (@ ~10-20m) multiple High Pressure Sodium Lamps. Both filters showed an improvement- The Marumi Redhancer more so. See ....

https://www.iceinspace.com.au/forum/...d.php?t=159955

Best
JA
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Old 11-07-2021, 09:35 AM
mandragara (Richard)
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Hi Richard & Hans,

Here is a comparison I did a few years back in Bortle 6 Brighton (SQM =19.14 & 2370 Ácd/m^2) of a couple of similar broadband didmyium type photographic filters (Hoya Intensifier V Marumi redhancer V no filter) with nearby (@ ~10-20m) multiple High Pressure Sodium Lamps. Both filters showed an improvement- The Marumi Redhancer more so. See ....

https://www.iceinspace.com.au/forum/...d.php?t=159955

Best
JA
Thats a very interesting comparison. Sadly where I live we have entirely transitioned to broadband LED streetlighting. Your comparison makes me even more nostalgic for the cyberpunk aesthetic of sodium street lighting
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Old 15-10-2021, 07:59 PM
Culford (Mick)
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I personally use an OIII filter to view various nebulae/ planetary nebulae. I own Lumicon and Astronomik filters, they both do a Stirling job.

I also possess a Lumicon (broad band) deep sky filter that I bought back in the day. This filter seems to have a subtle effect on some objects but to be honest I don't think broad band filters are worth purchasing.
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Old 15-10-2021, 09:21 PM
AnakChan (Sean)
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2 yrs back, I made a comparison of the different IDAS and STC filters :-

https://www.iceinspace.com.au/forum/...82&postcount=2
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Old 20-10-2021, 03:18 PM
ausastronomer (John Bambury)
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I also possess a Lumicon (broad band) deep sky filter that I bought back in the day. This filter seems to have a subtle effect on some objects but to be honest I don't think broad band filters are worth purchasing.
Hi Mick,

Funnily enough Broadband LPR filters actually do a really good job as Planetary Contrast Enhancement filters. Most people don't even try them for this purpose, but they work really well. They reduce irradiation, which improves the contrast between colour change boundaries.

As Don detailed earlier, they don't do much good as LPR filters under light polluted skies, but try it out on the planets

Cheers
John B
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