13 replies to this topic

[Wenxing Tang]

Hi all,

 

I'm planning on learning the sky with an 8" dobsonian. And I'm curious how much, if any, will a light polution/UHC/broadband/narrowband filter help improve the visual.

 

I tried to do my research on this, but it seems, just like any other topic in astronomy, people have very divided opinions on it. To make things worse, certain things also changed over time (tungsten light vs LED light).

 

That leads me to think maybe I should get a "not so narrow" narrow band filter (such as an Optolong L-pro or L-enhance).

 

So I'm curious: will this help at all? If so, what's the trade off? Will the view be a lot dimmer because of the filter? Will it be universally beneficial or just for specific type of targets such as emission nebulae?

 

Any thoughts/inputs is appreciated. Thanks!

 

p.s. if it helps evaluate my environment, the brightness at my location is about 18.73 mag/arcsec2 according to the light pollution atlas 2022.

[Keith Rivich]

Probably for your conditions a quality UHC filter would work best. Keep in mind narrowband filters help on certain nebulae but are useless on stars and galaxies. I have no experience with Optolong filters but I believe they are imaging filters and therefore would be useless visually. Any filter labeled "light pollution filter" is just as useless. They had some benefit in the incandescent street light days but are not helpful blocking modern LED's. 

[Jay_Reynolds_Freeman]

The answer depends on the nature of the light pollution at your site, and on what you want to observe. 

 

It is indeed true that the light sources used in outdoor lighting have changed a great deal during the lifetimes of many present amateur astronomers, from incandescent bulbs, to mercury-vapor and sodium-vapor lights, and now to LEDs. When mercury-vapor and sodium-vapor lights were major problems, one could use specially made filters to block much of their light and still leave plenty of starlight for observing; LEDs are more difficult to deal with.

 

Certain deep-sky objects emit most of their light at specific wavelengths; those objects include planetary nebulae and other kinds of emission nebulae. Filters are made which pass *only* those wavelengths of light, and allow observation of those objects even with substantial amounts of local light pollution.

 

So it is up to you to assess your site and figure out what you want to look at. Don't worry too much, there are things you can observe even in very light-polluted areas, like the Moon, the planets, double stars and many star clusters.

 

 

Clear sky ...

[Jethro7]

Hello Wenxing Tang,

I discontinued using light filters a long time ago for coventional viewing.Unless you live under dark skies, light filters are really a waste of money. Under light polluted skies these filters make everything very dark and the images of your targets like Emission Nebulae, planetary Nebulae are still very muted and disappointing at best.  First off, LED lighting is the worse and not much can be done about it other than doing your best to block it by hanging up a tarp or the like. Or in the case of LED streetlights, you may be able to have the county or municipal authorities have the streetlights skirted.  However there are options for dealing with other forms of light pollution.

 

These three options  actually work and the money you would have spent on the light filters would be better spent on one of these options. 

 

(1) - Travel to dark skies. Dark skies are always the best and by its self, or combined with the one of the other options can be especially amazing. 

 

(2) - Night vision Astronomy. (Very effective but very expensive) my preferred option.

 

(3) - EAA "Electronically Assisted Astronomy"  This Genre of Astrononmy is probably the most favored by Backyard Astronomers, of the options for viewing under light pollution. A complete set up for EAA, can be done for as little as  $349.00 - $499.00 with one of the new class of robotic telescopes like the ZWO Seestar S30/S50 where you will be able to actually see these Nebulae as well as countless other celestial objects that are far beyond what you will ever be able to see with your telescope. I also employ a Seestar for EAA, and these little gadgets are really cool.

 

HAPPY SKIES TO YOU AND KEEP LOOKING UP Jethro

Edited by Jethro7, 09 March 2025 - 01:57 PM.

[SeattleScott]

I believe the Optolong filters are designed for imaging. Camera sensors can see different wavelengths than the human eye.

UHC (narrowband) or OIII can help with nebulae. UHC is more general purpose if you want to start out with just one. OIII are optimized for planetary nebula.

Generally filters aren’t very useful for other DSO. Some people like them in light polluted environments, but any improvement is subtle, because you are generally dimming the target as much as the background sky. So it might present a more aesthetically pleasing view, but it isn’t necessarily improving contrast.

[therealdmt]

I’d get a narrowband UHC filter when you’re ready. It’s not something I’d get at the very beginning, largely because it’s just one more thing to have to fiddle with. When I started using filters (I think when I got my second one, an OIII), and was switching the filters in and out and the eyepieces in and out, screwing in this and unscrewing that, trying to keep track of where everything was in the dark, plus dealing with the telescope itself and the sky, that was the first time I said to myself, "Myself, you have got a lot of stuff" 

 

But anyway, after you can use your equipment smoothly (incl. having a few eyepieces and being able to select the right one, smoothly switch them in and out, refocusing as needed, etc.), have a good viewing spot or spots, have your setup, breakdown and transport routines down, and have found numerous objects and can use averted vision comfortably, then getting a narrowband UHC filter (or perhaps an OIII) is a logical next step. 
 

These filters, UHC narrowband and OIII, and there’s also a more specialized H beta filter, these are nebula filters. This is as opposed to the colored filters that some use for planetary viewing, plus there a few other specialized filters available for visual (ex. neutral density, semi-apo, etc.), and then there are completely different filters used in astrophotography. Anyway, these nebula filters help you see… nebulae. Don’t expect miracles — you still have to get out of direct glare, dark adapt and view with averted vision. But, if you do all these things and your conditions are decent, the effect can be quite dramatic. They aren’t general light pollution filters, unfortunately. They don’t help with galaxies, stars, globular clusters or open clusters, or, for that matter, even reflection nebula. They just help with emission nebulae (diffuse and planetary nebulae). Fortunately though, some of the most famous objects in the sky are emission nebulae. These include the Orion Nebula, the Lagoon, the Trifid, the Ring Nebula, The Dumbbell Nebula, and various others.

 

Meanwhile, general light pollution filters are sold, but, regrettably, they don’t help with LED lighting…  Unless you know that your local light pollution is not LED, you can pretty safely just skip buying a general light pollution filter. In general, they don’t work anymore (modern lighting). Of course if you want to experiment, it’s only money (heck, I bought one  ). But nebula filters do work, though still limited by conditions

[Dobs O Fun]

Hello Wenxing Tang,

I too have an 8" dob and live in heavy light polluted skies.

As all mentioned above are good information. Currently I do not use any filters, driving out of the area is an improvement. I wouldn't rule out filters as they can help but for the most part what I can see is largely dependent upon seeing conditions.

If you do get any filters it would be a help if you reported back with results! There will be others in the same situation as us in the future.

[Wenxing Tang]

Thank you all so much for the responses!

 

I believe I'm 30-40 min drive away from Bortle 4 and that's probably the easiest (and free) improvement I'll get. I'll try to get my routine down first before I invest in a narrowband UHC filter.

 

I'm asking now just so I can get some ideas on what works and whatnot and start watching classified listings in case any bargain comes up.

 

I'll make sure to report back and share my experience with the filter(s) in the future.

 

Thanks everyone for your inputs! Really appreciate it!

 

Clear skies!

[PKDfan]

Hi Wenxing Tang !

Welcome to CN !

The members have given you solid advice and i can add only a couple minor things not covered.

First is these filters are basically mirrors reflecting away all the 'noise' so nebular light can pass and dramatically increase contrast so if you buy one you must block all of your ambient light so that unwanted light doesn't enter through the eyepiece.

It does dim the view so you can't use high power. Exit pupils generally from 2mm to the widest your eyes can dilate to. Low powers and widefield eyepieces will give you the best views.

I have two expensive filters i haven't used yet so i bought them more as an investment when the right conditions and times arrive. An OIII and a UHC nebustar2. I used one with my C8 long ago and they improved the view enough for me to decide that getting another was a wise idea.

It does seem a bit foolish right now but i'm a longterm investment type person.

One last thing...the ones i bought have an efficiency rating and that number can vary a few percent so if you happen to be in an astro store check through them for the best efficacy.

Quite frankly you don't need them at all but are a great thing to have when you have everything else.

Good luck !


Lance
CSS

[Jon Isaacs]

Hi all,

 

I'm planning on learning the sky with an 8" dobsonian. And I'm curious how much, if any, will a light polution/UHC/broadband/narrowband filter help improve the visual.

 

I tried to do my research on this, but it seems, just like any other topic in astronomy, people have very divided opinions on it. To make things worse, certain things also changed over time (tungsten light vs LED light).

 

That leads me to think maybe I should get a "not so narrow" narrow band filter (such as an Optolong L-pro or L-enhance).

 

So I'm curious: will this help at all? If so, what's the trade off? Will the view be a lot dimmer because of the filter? Will it be universally beneficial or just for specific type of targets such as emission nebulae?

 

Any thoughts/inputs is appreciated. Thanks!

 

p.s. if it helps evaluate my environment, the brightness at my location is about 18.73 mag/arcsec2 according to the light pollution atlas 2022.

 

Hi:

 

Your skies are very much like my urban backyard.  Light pollution atlas 2022 rates mine at 18.65 mpsas, on a good night, I sometimes see that on my SQM-L directly overhead.  I am retired, I do a lot of observing from my urban backyard as well as from dark skies.

 

I am a cup half full kind of a guy so I appreciate the benefits of a narrow band deep sky filter even under bright skies.  An O-lll filter darkens the sky by about 3 magnitudes, that's a lot, that's like driving out to magnitude 21.5 mpsas skies.  A UHC filter darkens the sky glow by about 2.3 magnitudes.  The gain is only realized on certain types of nebulae but for those nebulae, they are very effective.  

 

A couple of nights ago, I had my 10 inch Dob out, the moon was bright, nonetheless, I was able to see NGC2440, a magnitude 9.3 planetary in Puppis.  It was pretty low but the O-lll filter made it possible to see it.   

 

Keith recommended a quality UHC filter, the bandwidth should be less than 30nm. There's a nebula filter guide pinned to the top of the eyepiece forum... There is lot to be said for a narrowband UHC filter but for observing under light polluted skies, I tend towards an O-lll filter as it darkens the sky by a factor of 2 compared to a UHC filter.  Some nebulae are O-lll only, many are O-lll + H-Beta.. From dark skies, a UHC provides the widest coverage but from light polluted skies, an O-lll filter can give you the best chance.

 

It's best to buy 2 inch filters. They can be used with 1.25 inch eyepieces so in the long run, you save by only having to buy one filter.

 

My best to you and yours and enjoy your 8 inch Dob.

 

jon

[aeajr]

Hi all,

 

I'm planning on learning the sky with an 8" dobsonian. And I'm curious how much, if any, will a light polution/UHC/broadband/narrowband filter help improve the visual.

 

I tried to do my research on this, but it seems, just like any other topic in astronomy, people have very divided opinions on it. To make things worse, certain things also changed over time (tungsten light vs LED light).

 

That leads me to think maybe I should get a "not so narrow" narrow band filter (such as an Optolong L-pro or L-enhance).

 

So I'm curious: will this help at all? If so, what's the trade off? Will the view be a lot dimmer because of the filter? Will it be universally beneficial or just for specific type of targets such as emission nebulae?

 

Any thoughts/inputs is appreciated. Thanks!

 

p.s. if it helps evaluate my environment, the brightness at my location is about 18.73 mag/arcsec2 according to the light pollution atlas 2022.

I live with Bortle 8 conditions, 25 miles outside of NYC in a very populated, very illuminated suburb. Lots of ground and sky light pollution. I can read a book in my driveway based on the street lights in front of my house.  All of the lights have gone to very bright white LED.

 

Portions of my sky have no stars below mag 2.  My best direction on a moonless night gives me a NELM, naked eye limited magnitude of about 3.7, maybe 3.5, but that is a small part of the sky.  I can get to Bortle 6 in about 40 minutes and Bortle 4 in about an 90 minutes, but most of my observing is done from home in 60 to 90 minute sessions.

 

I am no expert on filters, so I am just passing on my personal experience.  I bought most of my filters when I had my original 80 mm achromat and my 8"/203 mm Orion Dob so I bought them all 1.25"   

 

There is no "one size fits all" filter.  Just like wrenches, you will need different filters for different situations.  Trying to get a multipurpose filter, like an adjustable wrench, may help but it can't do the job as well as a specific purpose tool. 

 

This is my experience, your smileage may vary. 

 

 

I have 3 light pollution filters.  One is the Orion SkyGlow/Lunar filter.  I also have two generic light pollution filters. I don't use any of them anymore.  They don't really seem to help much if at all since the LED street lights were put in. 

 

 

True narrow band nebula filters are a huge help.  You want very narrow passbands in the OIII or OIII plus H Beta bands with everything else blocked out.  Examples would be DGM NPB, Orion Ultra Block, Lumicon UHC. 

 

I believe the Lumicon UHC is the source of the UHC term.  These are very narrow passband filters.  These are for use on nebule.  And their effectiveness will vary depending on what type of nebula you are viewing.  They are not likely to help you much, if any, with galaxies or other deep sky objects. 

 

The term UHC has been adulterated from its original meaning. Many of the UHC filters on the market today are not narrow band and let through other lines, so be careful what you buy.  They may help on nebula but they are not the best choice.  If you are looking for a narrow passband nebula filter, make sure you know what lines are being passed. 

 

Some say the wider band filters, while not as effective on nebula, may be some help on galaxies.  I have not tried this.. 

 

As you are using an 8" Dob, which should have a 2" focuser, I would suggest you consider 2" nebula filters that can be attached to the focuser, if it is threaded, or the 2" to 1.25" adapter, if it is threaded.

 

Some nebula are observed at very low power and may benefit from using a 2" low power eyepiece.  Some benefit from high power.  A 2" on the focuser will let you switch eyepieces without having to unscrew and dismount and remount filters on your eyepieces. When I bought my filters I was using them on a 1.25" only 80 mm scope as well as 2" 8" Dob.  Today I would buy 2" as my 2 main scopes have 2" focusers.

 

 

Planetary filters provide subtle help when viewing planets.  Many say they are not worth it.  Some find them useful.  I have used the cheaper ones and have found them useful in teasing out specific details, but the difference is very subtle.  Most of the time I don't use them.  Perhaps the more expensive ones work better, but I could not say.

 

 

Lunar Filters - These are basically sun glasses for the Moon.  While not required I do find that a 25% lunar filter, when the moon is 1/4 or brighter, is helpful. I do most of my lunar observing along the terminator line.

 

I have also found this filter helpful on Venus when it is very bright.  My main lunar filter is a low cost 1.25" Orion 25% on all of my scopes from 80 mm to 305 mm.  I believe it is a rebadged GSO 25% filter.   I mostly use this on my zoom eyepiece so there is no filter changing required. 

 

As I am normally viewing the moon at high power, I don't feel the need for a 2" filter but lunar filters are inexpensive and attaching this to the adapter will make it easier when working with fixed FL eyepieces. I also have an unmarked lunar filter that I estimate to be about 40% pass through, but I rarely use it. It came as part of an inexpensive filter kit. 

 

 

Solar Filters - I use a white light full aperture filter on my 80 mm achromat and also have one for my 127 mm Mak.They re made from that are made from film, not glass.  They work great and are very inexpensive.  I also have these for my 50 mm binoculars, DSLR and my 50 mm finder.  They were especially useful during the Lunar eclipse.  I managed to travel to see the total eclipse.

 

So, that is my experience and my suggestions, for what it may be worth. The actual filters I have are listed in my signature. 

 

You may find the article on filters useful.

 

 

Ed’s Beginner Resource Guide - Revision 2
Part 2 - ONCE YOU HAVE YOUR TELESCOPE
https://www.cloudyni.../#entry12639891

Edited by aeajr, 09 March 2025 - 10:58 AM.

[Wenxing Tang]

Great! Thank you everyone for sharing your experience and insights! Really appreciate it. I'll definitely read the pinned post as well as the beginner resources guide.

 

Clear skies!

[Peter Klein]

How helpful are the filters that cut the wavelengths emitted by sodium vapor lights? I live about 12 miles north of downtown Seattle, Bortle 6-ish. Street lighting is mixed, some sodium vapor, some conventional or LED. Would I be better off with a sodium vapor filter or something like the Astronomik UHC Filter?

Like the OP, I’m most interested in visual observation, not astrophotography. So far I’ve mostly observed the moon and planets. I definitely need an ND filter for the moon. As I do more deep sky, I may need some filtration. My scope is a Sky-Watcher Vituoso Gti 150p.

[David Knisely]

Although you may have seen this (and the particular products being mentioned are a little dated), this article does cover the basics of filters intended for deep-sky use:  https://www.prairiea...ep-sky-objects/

 

For general recommendations, I would go with a good narrow-band nebula filter like the Astronomik UHC filter, the DGM Optics NPB filter, or (if you can get one) the Lumicon UHC filter.  They should have full-width and half-maxima bandwidths of less than 30 nm to be very effective, but not much narrower than 21 nm.  Remember that the label "UHC" does not necessarily mean a true narrow-band nebula filter, as it is often stuck on much broader filters.In addition, a good Oxygen III line nebula filter will also work wonders for many planetary nebulae and some diffuse emission nebulae.  Make sure that OIII filter has a bandwidth of between about 12 nm and 9 nm.  The broadband filters like the so-called "UHC-S" and others tend to not be terribly effective under moderate to severe light pollution, and even under a dark sky, the improvement of the view is often somewhat marginal.  Good luck and clear skies to you.