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Are light pollution filters needed?

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#1 rannar

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Posted 21 March 2019 - 10:03 AM

I seek to observe visually, and from what I see light pollution filters are only really needed for astrophotography. I am in a Bortle Class 8 sky, seeing only about 30 stars with the naked eye. I am most likely going to use a 6" dobsonian. Would a filter be needed?


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#2 SeattleScott

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Posted 21 March 2019 - 10:27 AM

Needed, yes. Available, no. Light pollution filters primarily only help for viewing nebulae. Modern broadband lighting has made light pollution filters obsolete.

A couple nights ago I was experimenting with my new Moon and Skyglow filter. After a lot of back and forth I decided that I think I like the view a tiny bit better with the filter. So a tiny improvement from a $130 filter. Which is better than my previous $50 LP filter, which made the view worse. Mostly I got the M&SG for viewing Jupiter, or pairing with a Fringe Killer on my achros. Light pollution is a secondary consideration and kind of the icing on the cake.

Scott

Edited by SeattleScott, 21 March 2019 - 10:32 AM.

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#3 Mr. Mike

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Posted 21 March 2019 - 10:35 AM

Yeah - I just dont think it ends up worth it or whatever.  Try to get to better skies or accept that there will be viewing limitations.  I know, sucks but thats basically the issue! :(


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#4 Sam M

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Posted 21 March 2019 - 10:38 AM

+1 on what Scott said.  Specifically, narrow band or OIII filters can help a bit with emission nebulae.  So, M42, M27, that sort of thing.  For galaxies, there's no real help that I've seen.  I drive to dark(er) skies.  That is very effective.  That said, there are plenty of things to look at through light pollution. Moon, planets, open clusters, globular clusters, carbon stars, double stars, etc.  So you can still have fun at home.



#5 penguinx64

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Posted 21 March 2019 - 11:34 AM

A lot depends on the light pollution source.  I have good results using a moon & skyglow filter for sodium vapor and fluorscent lights, but not so good for halogen or LED lights.  I recently picked up a Baader Contrast Booster filter and it seems to help more.


Edited by penguinx64, 21 March 2019 - 11:39 AM.


#6 gnowellsct

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Posted 21 March 2019 - 11:40 AM

Needed, yes. Available, no. Light pollution filters primarily only help for viewing nebulae. Modern broadband lighting has made light pollution filters obsolete.

A couple nights ago I was experimenting with my new Moon and Skyglow filter. After a lot of back and forth I decided that I think I like the view a tiny bit better with the filter. So a tiny improvement from a $130 filter. Which is better than my previous $50 LP filter, which made the view worse. Mostly I got the M&SG for viewing Jupiter, or pairing with a Fringe Killer on my achros. Light pollution is a secondary consideration and kind of the icing on the cake.

Scott

The neodymium filter gives excellent views of Jupiter and Mars.  Forget the light pollution, though.  

 

The best light pollution filter is a car.  Put the scope in the car and drive away from the lights.  If you're going to observe in heavy light pollution, do Moon and Solar.    This is probably the biest reason to get a refractor instead of a dob as a novice.  An 80 to 100 mm refractor can be fitted with a daystar quark and give awesome results.  At night you can use it on the moon.  Jupiter, Saturn, and Mars will be OK when they're around.  

 

Greg N

 

Greg N


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#7 Simon B

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Posted 21 March 2019 - 12:58 PM

Just reiterating, but

 

 

By FAR the best light pollution filter is petrol : )

 

 

The second best light pollution filter would be a UHC - here is a great article describing filters:

 

https://www.prairiea...ep-sky-objects/

 

 

Do they work under a Bortle 8 sky with a 6 inch dob? Sort of... you'll probably get moderate enhancement of brighter nebulae like M42, M8, M20

 

But: dark skies + no filter = much better than light polluted skies + filter.... better still, is dark skies + filter!


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#8 SteveG

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Posted 21 March 2019 - 02:41 PM

 

 

By FAR the best light pollution filter is petrol : )

 

Or in my case, electricity....  :-)


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#9 Simon B

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Posted 21 March 2019 - 03:29 PM

Or in my case, electricity....  :-)

 

Ah, touche grin.gif


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#10 rannar

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Posted 21 March 2019 - 06:05 PM

Thanks for the advice everyone!



#11 vtornado

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Posted 21 March 2019 - 08:32 PM

I live in a red zone.  I have an orion ultra block filter.  It helps on a small handfull  of nebula.  I would buy one used, and see if you like it.

If you don't like it you can pass it on, and not lose very much money.


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#12 RalphMeisterTigerMan

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Posted 21 March 2019 - 10:29 PM

You have to remember that "light pollution" filters were first introduced while street lights still used Mercury Vapour lamps. Not long after the filters became popular, most being sold by Lumicon, cities all over North America were switching over to High pressure sodium lamps. While only the "sky glow" type filter actually, marginally, helped with the light-pollution produced by mercury vapour, there was and is no such thing as an actual "light-pollution filter". 

 

Nebula filters only work on certain types of Nebula by blocking out most light and allowing the very specific "oxygen lines" to come through, these are the U.H.C. and Oxygen III filters. The H-beta filter is an extremely discriminating filter working best on the California and Horsehead nebula. 

 

There no such thing as a filter that will help for visual use on Galaxies, Globular, open/tight clusters. So, "light-pollution" filters are very much like the "dark side of the Moon", non existent and a miss-nomer. Believe me, I wish they were real because I for one could really make use of such a device.

 

Reality bites. RalphMeisterTigerMan



#13 Starman1

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Posted 28 March 2019 - 03:33 PM

I seek to observe visually, and from what I see light pollution filters are only really needed for astrophotography. I am in a Bortle Class 8 sky, seeing only about 30 stars with the naked eye. I am most likely going to use a 6" dobsonian. Would a filter be needed?

Broadband nebula filters are sometimes called LPR filters, but seriously, the best and only filter to get to observe in your area will only help in viewing nebulae.

It's a "narrowband" or "UHC-Type" filter, and it definitely will enhance your views of nebulae like M42/43 in Orion.

As for all other objects, there is a slight edge to merely increasing the magnification.

Though increasing the magnification will dim the object as well as the background sky, the fact the object becomes larger may aid in observation.

This especially works well on star clusters and globulars because they don't dim with magnification, but the background sky does.

100x will be a better observing magnification than 50x, for example, for objects helped by magnification.

 

In a city, what can you see (I speak from experience, living in L.A.)?

Moon

Planets

Open star clusters (bright)

Globular star clusters (bright)

Carbon stars

Double stars

Bright emission nebulae (using a filter)

 

For galaxies, fainter nebulae, fainter and smaller clusters, comets, etc, transport the scope occasionally to darker skies, where you can see these things well.

 

To aid in viewing things in the city:

--view AFTER it gets dark (90 minutes after sunset) and not before

--become dark adapted (at least 30-45 minutes outside under the stars before you start observing) unless looking at the Moon.

--block or turn off any light you can see directly.  No house lights, yard lights, or streetlights visible directly.  You can block any light you can't turn off with panels and supports.

See: http://jaysastronomy...ht-shields.html

--view all objects at least 30° up from the horizon.  The air is 2X as thick at 30° than it is at the zenith.  Below that is muck.

--don't view objects directly over a roof if you can avoid it.  Heat is given off by roofs all night long and causes the image to blur.


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#14 aeajr

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Posted 28 March 2019 - 03:57 PM

I seek to observe visually, and from what I see light pollution filters are only really needed for astrophotography. I am in a Bortle Class 8 sky, seeing only about 30 stars with the naked eye. I am most likely going to use a 6" dobsonian. Would a filter be needed?

I am also in a Bortle Class 8 location and I feel  your pain.  I have several scopes. 

 

 

 

The challenge of observing in a light polluted area is understanding light pollution and its effects on what you are observing.

 

Light pollution filters are becoming less and less effective.   These are tuned to the frequencies that are produced by Sodium and Mercury vapor lights.  But those are being rapidly replaced by white LED lights.   Light pollution filters don’t work for LEDs.  I have two light pollution filters and I have not seen any significant benefit from using them.   Most of my area now has white LED lights.

 

So the key to success and enjoyment is picking the right targets for your circumstances.

 

These are targets that are less affected by light pollution when using binoculars or a telescope.  

  • single stars
  • star clusters
  • planets
  • the Moon
  • double stars (which appear to be single stars)
  • The Sun (with required solar filter)

Targets that are more affected by light pollution when using binoculars or a telescope. 

  • Galaxies
  • Globular Clusters
  • Most Nebula of all types

Of course, there are exceptions.  For example, there are some very bright nebula that can be seen in fairly light polluted areas, such as the Orion Nebula.


There are two kinds of light pollution, sky and ground.  The dark site finder only reflects sky light pollution.   www.darksitefinder.com

 

Ground light pollution reflects your immediate surroundings.   House lights, street lights, parking lot and building lights, cars going by, the display on your phone, etc.   These keep your eyes from dark adapting and that affects what you see in the eyepiece.  The darker the ground area the better your vision for observing.   Ground lights also produce reflections and side light on the aperture lens, mirrors and the eyepieces.  You can get ghosts in the view that are really caused by ground light.  I once thought I saw a comet tail.  Turned out it was stray light coming from my neighbor’s house light.  Using a dew shield on your telescope can help shield the optics from stray light.  I even have a dew shield for my 8” Dob for this reason.

 

Sky light pollution reduces the contrast between what you are looking at and the surrounding sky.   All those stars are there during the day, we just can't see them because of the all the light pollution caused by the Sun.  The sky is brighter than the stars so there is no contrast which means we can’t detect them with our eyes.   But if you turn a telescope to the sky during the day you may be able to see some of the brighter stars, just stay way away from the Sun.  

 

Likewise a full moon lights up the sky and reduces contrast between your targets and the surrounding sky.    As noted above, some things are more affected by sky light pollution than others.

 

Magnitude - You will see stars rated by magnitude.  The higher the number the dimmer the star.   The more sky light pollution you have the brighter the stars have to be for you to see them naked eye.   You will read this referred to as NELM, naked eye limiting magnitude.   So the NELM refers to the dimmest star you can see, naked eye, near the zenith or in your best direction when there is no moon.  Remember that this will be affected by both sky and ground light pollution.   For me NELM is between Mag 3.5 and 3.8 which is pretty bad.  And when there is a full moon I can easily count all the visible stars in the sky, which is not many.

Magnitude
https://en.wikipedia...arent_magnitude

The Bortle scale is one way that we rate the light pollution in the sky.  On this scale my home is around Bortle 8.
http://www.bigskyast..._bortle.html   

It is also helpful to understand the difference between the magnitude of a star, which is a point of light, and the magnitude of things like galaxies and nebula which may be rated at mag X because of the amount of light they put out but that light is spread out over a large area.   So a Mag 4 star might be easily visible in your sky but a Mag 4 nebula likely will not be visible.   The difference is surface brightness.

Magnitude vs. Surface Brightness
https://www.cloudyni...g/#entry8521236


Picking your targets

Net net, when I am observing from home, which is 80% of the time, I go for stars, brighter star clusters, double stars, the Moon, planets, and the brightest globular clusters and nebula.     If I am at a darker site I may shift my priorities to globular clusters, nebula, and galaxies which are difficult or impossible from home.

There are a variety of ways to pick your targets.   I like to create a list of targets sorted by constellation using Tonight's Sky.  I pick those targets that make the most sense for my area.   And experience has given me an idea of what magnitudes I can see in star clusters, nebula and the like.    Experience will help you judge what levels to select for your area.
http://www.cloudynig...ights-sky-free/


Hope that helps as one light pollution limited observer to another.


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#15 sg6

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Posted 28 March 2019 - 04:15 PM

You have to work out what the main characteristic of the light pollution is. Then work out what filters may, only may, improve the situation. However since a filter removes something the result will be a view with that portion of the spectrum removed.

 

As usually these days the light pollution is fairly wide it is becoming more and more difficult. If someone puts an LED in a street lamp that emits at the OIII wavelengths, 500.7 nm and 495.9 nm - or close, then that will wipe out the usefulness of the customary nebula filter.



#16 silv

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Posted 04 April 2019 - 07:35 AM

Does anyone else experience something like a physical shock when reading advice like "best nebula filter is petrol"? I'm amazed how conscious I grew since last August when I read https://www.pnas.org...ent/115/33/8252

 

I'm also observing from a city location and decided against filters. (And I don't own a car.) There's enough beauty to behold for us through a scope from where we live. It's well worth it!

As long as you just want to enjoy a couple of hours of wonders  now and then and don't want to make observing into a sports activity with ticking off the DSOs of a soulless list or something. 


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#17 SeaBee1

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Posted 04 April 2019 - 08:45 AM

Light pollution, the night sky observer's bane... as Ed above has said, it is a challenge to be addressed; not a reason to give up! As many have mentioned, it's all about the target selection. Filters can enhance some targets, but it isn't the true fix. Dark adaption can help, but the target/sky contrast isn't mitigated. Experience will help as well. But, sadly, the best way to mitigate the LP curse is to drive away from it.

 

So, since I do all my observing from my LP infested home site, my targets have to be LP resistant. Planets are first up if they are up. Then the Moon. Next are double/multiple stars. After that comes open clusters. And finally, as a way to thumb my nose at the LP demons, I use a Coronado SolarMax II DS60 for HA viewing of the Master light polluter.

 

Would I like to view galaxies and nebula? Why yes I would, but that will be for another time, perhaps when I retire, and I have no work/family pressures to deal with. The nice thing is, those targets will still be there when I am ready...

 

While others may recommend certain filters, I would recommend saving your money and just select targets that are LP resistant. And if circumstances avail, drive to a dark site when possible...

 

Good hunting!

 

CB


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#18 Starman1

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Posted 04 April 2019 - 10:12 AM

Does anyone else experience something like a physical shock when reading advice like "best nebula filter is petrol"? I'm amazed how conscious I grew since last August when I read https://www.pnas.org...ent/115/33/8252

 

I'm also observing from a city location and decided against filters. (And I don't own a car.) There's enough beauty to behold for us through a scope from where we live. It's well worth it!

As long as you just want to enjoy a couple of hours of wonders  now and then and don't want to make observing into a sports activity with ticking off the DSOs of a soulless list or something. 

So I power my house with solar panels, water my plants with rain water or "grey" water, flush my toilets with shower capture (converting to waterless native plants later this year),

heat my home only to 64° all winter, and drive a small, high-mileage, car.

 

You're absolutely right, though, but that would mean people like me would observe very little at all. Los Angeles is a very bright city.


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#19 alexantos

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Posted 04 April 2019 - 02:25 PM

I seek to observe visually, and from what I see light pollution filters are only really needed for astrophotography. I am in a Bortle Class 8 sky, seeing only about 30 stars with the naked eye. I am most likely going to use a 6" dobsonian. Would a filter be needed?

Hi rannar,

 

I'm in the same condition as you regarding the Bortle 8 situation. For now, I'm observing without any filters at all, so if you want to check what I'm able to see, check out this topic that I've started.

 

Take care.



#20 Starman1

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Posted 04 April 2019 - 05:04 PM

As for whether filters help in a city, consider this:

This is approximately how M42 appears in LA without a filter, using my 4" apo:

https://www.google.c...HXJIWUT1Jtk2BM:

And this is approximately how it appears with a good UHC in the same scope:

https://www.google.c...sK4CxHw3yvoFpM:

but without the color, of course.

 

But this is approximately how it appears at my dark site, using the same filter, with my 12.5":

https://www.google.c...VCuyBs9H4pLK-M:

and, again, without color.

 

Filters are extremely useful on emission nebulae, and make all the difference in the world as to how things appear.

I don't have a lot of use for broadbands (aka "LPR filters"), but a good narrowband is worth every penny.

I can't see the Veil without one, here in LA.


Edited by Starman1, 04 April 2019 - 05:05 PM.

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#21 Simon B

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Posted 04 April 2019 - 08:39 PM

Does anyone else experience something like a physical shock when reading advice like "best nebula filter is petrol"?

 

You're right, perhaps that was a bit discouraging... what I meant to say was, filters, especially 'broadband' light pollution filters, won't exactly work magic on deep sky objects from the city - UHC / O-III filters would be the most effective in combating light pollution, they do somewhat help

 

If it's at all possible, getting out to darker skies makes a enormous difference - much more than any filter could. There's so much marketing around these filters that exaggerate their effectiveness. Petrol really is the best filter! But if you're stuck in the city, a UHC / O-III will show subtle enhancement

 

Sorry to OP if that was dismissive advice, it wasn't meant to be


Edited by Simon B, 04 April 2019 - 08:41 PM.

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#22 Jon Isaacs

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Posted 05 April 2019 - 04:12 AM

I'm also observing from a city location and decided against filters. (And I don't own a car.) There's enough beauty to behold for us through a scope from where we live. It's well worth it!

 

As long as you just want to enjoy a couple of hours of wonders  now and then and don't want to make observing into a sports activity with ticking off the DSOs of a soulless list or something.

 

I spend a lot of time observing, 500-600 hours per year.  It's split about 50%-50% between my urban backyard and dark skies.  

 

It's by no means a soulless, sports activity.  It's an aesthetic-spiritual-intellectual experience that's rewarding/satisfying on many levels. I am not one who works from a list , I let the moment and serendipity guide me. 

 

There is a lot to see.  Filters are just one the tools one can use to enjoy the night sky,  to see more , to see things otherwise invisible.  20 years down the road,  you may have developed a passion for observing the night sky and filters will make more sense. 

 

Jon


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#23 Carlos Flores

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Posted 15 April 2019 - 08:02 AM

A lot depends on the light pollution source.  I have good results using a moon & skyglow filter for sodium vapor and fluorscent lights, but not so good for halogen or LED lights.  I recently picked up a Baader Contrast Booster filter and it seems to help more.

I bought the Sky&glow a couple months ago, but as penguinx64 mentioned, it did not work well with the new LED lamps installed in the small yard besides my apartment. Probably i was putting too much expectations on the improvement provided by a filter which dimmed the view a little bit. 

 

I ended moving my observation spot a couple of meters sacrificing some field but gaining more darkness, and i also added a longer dew cap to block stray light and finally I use a hood to improve the contrast at the eyepiece.

 

Carlos


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#24 Illinois

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Posted 16 April 2019 - 08:45 AM

I grew up in Chicago and I use light pollution filter but it don't help much! Depends on deep sky objects. It helped that I able to see faint M8 Lagoon nebula, few other and that is it. I like open clusters best that I can see it without a filter in Chicago! I can see faint NGC 7331 and M110 in my 10 inch dobsonain in Chicago. Not use light pollution filter for galaxies. Little darker sky like Yellow zone and UHC Filter is useful that I can see Veal Nebula in yellow zone.

Edited by Illinois, 16 April 2019 - 08:48 AM.


#25 rannar

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Posted 22 April 2019 - 09:30 PM

Okay, I see light pollution filters are pretty useless.

 

Are nebula filters worth the money? And what are the basic color, or planetary filters?


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