Light Pollution filter recommendations?

[Richyboy24]

hey everyone,

i'm interested in buying a light pollution filter for my 250px Skyliner Dob. Living to the east of London i get a fair amount of light pollution, especially in the West, south west.

can anyone recommend some filters for me that might help me get rid of some of the truly appalling London glow that i suffer from?

Cheers!

[George]

I use a Astronomik CLS Filter http://tinyurl.com/3xztq3 both visually and for imaging, light pollution is moderate to heavy in my location & this filter deals with it no problem.

[Astronut]

I've just taken delivery of an Astronomik UHC filter but I haven't had chance to try it out yet. I only want the one filter to be going on with and it's generally recommended that a UHC is the one to go for if you only want one filter. It has a narrower bandwidth than a 'Deep Sky' or LP reduction filter but I wanted one that would increase my chances of seeing nebulae as well as cutting down on light pollution.

Filters come in two sizes for 2" or 1.25" eyepieces so if you have or are planning to get a 2" eyepiece it would be better to get a 2" filter. You can screw the 2" filter into a 1.25" eyepiece adaptor (but unfortunately the Skywatcher 2/1.25" eyepiece adaptors are not threaded for 2" filters). UHC filters are not recommended for small 'scopes because of the light loss but a 10" reflector should cope quite easily.

There's the Astronomik CLS filter which has a broader bandwidth and is cheaper. I was torn between the CLS and the UHC but after reading a few reviews and talking to the dealer I opted for the UHC.

The Baader Neodymium filter is not expensive but from what I've read it's more useful for astro imaging than for visual use (others who own one will be able to give a more informed opinion). A 10" 'scope will be able to cope with narrower bandwidth filters though.

There's also the Baader UHC-S which seems popular. I've been led to believe the bandwidth of this filter is slightly wider than the Astronomik UHC but I'm not sure about this.

Here's a good link for general filter comparisons - think of the 'deep sky' filter referred to in that link as a general purpose broadband LP reduction filter.

[John]

I've used a Baader UHC-S filter for a while now with a wide variety of scopes and I've found it pretty effective on nebulae and in particular planetary nebulae. I've recently got a Baader OIII filter but I only plan to use that with my 8 inch scope as it's a bit too narrow for smaller apertures I've found.

I did try a Celestron LPR filter and the Orion Skyglow filter in the past but I did not find those to be very effective TBH.

The general advice that I have picked up is that the narrowband filters such as the UHC and UHC-S are the most effective overall and if you only want to get one those are the type to get.

John

[Whippy]

You've basically got two types of filter. Products like the Astronomik CLS, Baader Neodymium and Celestron LPR filters are general light pollution filters, they cut out (to varying degrees) light pollution from sources such as street lamps whilst trying to keep as much light from celestial objects coming in. Some people think they do a great job, some don't. It's one of those accessories that works for you or doesn't.

You've also got what are called narrowband filters like the UHC/UHC-S filters, these only allow certain light frequencies that are emitted by certain objects like Nebulae for example to come through and cut everything else out. Whilst these are great for Nebulae, they don't allow starlight in so they're useless for galaxies, clusters and anything else where starlight is the source of the light emitted. Personally, I wouldn't call these light pollution filters as they cut out other light as well but in the context of this thread, I'll go along with it .

I've got a Baader Neodymium filter that for me visually, did nothing. I actually preferred looking at objects without it, but when I started doing afocal imaging, it's worked a treat. I've recently picked up a Hutech LPS filter which is supposed to be the business but I haven't had the chance to use it yet visually or for imaging so we'll see how that one goes.

I've also got a UHC filter which works a treat visually, it really works well on objects like the Ring Nebula and the Dumbell, bringing out lots more detail than you would normally see. But just be aware, you'd be wasting your time tyring to look at the Andromeda galaxy with one!

Tony..

[acey]

I have a Lumicon UHC filter which I use on nebulae. I've never had any problem with it on a small scope - I've used it to view M76 from my light-polluted back garden with an 80mm short-tube refractor. Mostly I use it on my 8-inch dob, though.

The UHC is very good for enhancing emission nebulae (the most common type) - but its effect on galaxies (and ordinary starlight) is only to make them dimmer, so it's no use if you're looking for something that will make galaxies easier to see in a light-polluted sky. Similarly, it won't help you see reflection nebulae (eg the Pleiades luminosity).

Emission nebulae radiate light at particular wavelengths and the UHC is designed to allow these through, and not much else. Streetlights (and stars) emit light at a very broad range of wavelengths, so it's a lot harder to filter one from the other. I've never tried any "skyglow" filters but its important to distinguish them from nebulae filters which are designed for a different job. I get the impression that the people who like skyglow filters best are the ones who suffer least light pollution to begin with, though maybe I'm wrong. But I'm really pleased with the UHC and think it's well worth the investment, as long as you understand the limitations.

I've never bothered getting an OIII filter as the UHC does a good enough job for me. I've been tempted by an H-beta filter so as to try and see the Horsehead nebula, but that's a lot of money for something so specialised in application.

One small point - because the UHC is designed to block most wavelengths, it's highly reflective, like a little mirror. If you're viewing at a place with too much stray light, you can get obtrusive reflections coming back at your eye from the filter. That might be another argument against using it in heavily light-polluted situations.

(I was slow to post this and I've repeated some information supplied meanwhile in the previous post - apologies for redundant info!).

[Richyboy24]

thanks for all the info, i'm am currently leaning towards the Baader Neodymium filter, which at £30 isn't bank breaking either!

so far i haven't had the best of luck with clear dark nights since getting my 250px Dob so i'm hoping over the next few weeks or so to really get a chance to see what this scope can do...i've certainly heard great things!

now if only London didnt exist and i could get lovely dark skies every time...

[dogfish]

I've got the Neodymium filter and have found it useless visually, I also loaned it to a pal with a 12" Dob and he couldn't notice any difference either. I'm keeping it for future astrophotography usage though.

My Recommendation - use the money for petrol to get to a dark site. I am completely sold on dark sites now and only bother setting up in the back garden of my suburban home for viewing/imaging the moon and planets. I'm lucky in that there are pretty good skies half an hour from my house and I've got some pals to go with.

HTH, Martin

[acey]

I'm with Martin on this, there's no substitute for dark skies - but for some people that's not really an option on any kind of regular basis. My understanding of the neodymium filter is that it filters the wavelengths of low-pressure sodium lights - the old-fashioned orange ones. Nowadays they're mostly high-pressure sodium which has a broader spread of wavelengths, and the neodymium can't help with that. But it is possible to observe nebulae from a light polluted site using nebula filters (and a hood over your head to eliminate stray light at the eyepiece). I've heard of someone viewing the Horsehead in this way with an H-beta filter. Never got one of those myself, though, as it's a lot of money for something that's effective on only a handful of objects.

Andrew

[nitram100]

I live in West London and use a baader planetarium neodyimuim filter and it does help out alot. I couldn't see the great red spot on Jupiter or the cassini division with my 10" orion optics scope until i used this filter. Nebulas such as M42 are much better with it also. This thing has it's work cut out for it that's for sure, as i can see 8 street lights from my backgarden, it's like a friggin disco. I picked mine up for 13 quid from astrobuysell.com. If you're ever near Harrow, you could pop over to me and i could lend it to you for a bit if you'd like, to see if it's worth you buying one.

[Macavity]

I think one CAN gain something by checking out the "transmission curves" of filters - And even taking them outside and seeing if they have a (useful, practical) effect on LOCAL street lighting etc. But some of this is up to "personal belief" too? FWIW, I have some faith in e.g. the Baader "Contrast" filter (the Neodymium for Achromats) - Seems to work? And I did buy myself the Baader UHC-S filter recently - Interesting effect to ponder, if nothing else...

[Beyond_Vision]

I totally agree with what Tony (Whiplash) has already said.

Regards

Kevin

[Guest]

hi. as far as i can make out, these light pollution filters or nebulae filters tend to make nebulae clearer but galaxies dimmer due to the different frequencies of light they emit. is that true? in which case how do they effect the viewing of planets?

[tim r]

Hi i use a baader neodyimuim filter and it works very well it's the 2" one and i think it was £45 would recommend.