Light pollution filter

[Spacerock]

Hello. Today's question is around the need for a light pollution filter. My garden has around 70% sky visibility -the outh east is slightly blocked due to houses and trees. It's pretty dark but there is a relatively close sodium (yellow) street lamp.

Would a light pollution filter help negate the effects of this? If so, which one to choose?

[NGC 1502]

Opinions are divided as to how well LP filters work, or even if it's worth having one at all.

(It's a different story for more specific filters for deep sky, here a UHC filter is the usual best buy advice)

This link http://www.prairieastronomyclub.org/resources/by-dave-knisely/some-available-light-pollution-and-narrow-band-filters/

is worth a read. It's a bit long, but there is no easy "one size fits all" solution for the curse of light pollution.

If it were me, I'd try to erect a shield to block that street light. I've tried several DIY shields. I put a tarpaulin over my wife's greenhouse to block lights in that direction,

and I have a plywood panel on poles that clamps to a fence to block lights in a different direction. Of course, every situation is unique as to what could help.

If you use a tarpaulin, most of the cheapos on sale are a bit thin to block light, so I use mine doubled, and clamp it with industrial pegs to stop it flapping in a breeze.

Hope you find a solution to help, Ed.

[hemihaggis1]

• contact local council , tell them the light is detracting for your enjoyment of your garden ,ask for a shield to fitted to the light , light pollution is a statutory nuicence ,and can be delt with by enviromental health
  

[Stu]

One comment with filters is that they all tend to improve contrast but at the expense of dimming the view. This means that good dark adaptation of your eyes really helps to get the best out of them. This can be tricky if your site isn't dark....bit of a viscous circle.

The previous suggestions make alot of sense to try first. Even some form of hood to shield your eyes would help but then you run into problems of steaming up! Just try to get your immediate observing position as dark as possible and so that you don't have to look directly at any lights. Don't use a tablet or laptop either as this will kill your vision.

Stu

[Qualia]

Ay, NGC has hit the proverbial nail on the head.

If you're suffering from sky-glow (that orange, cancerous hue we call LP) then there might be filters which could help. However, if that street lamp is causing glare, so that its light is entering your eye or telescope, well, that is a completely different story. No matter what filter you used, you'd still be getting glare which impairs everything that can be seen. If this is the case, then as NGC has suggested, you might want to build some kind of shield. If the former, you might want to have a look at the possibilities opened by filters such as an Astronomik UHC or CLS, Baader Neodymium, Baader UHC-S etc.

[ronaldo999]

i have used a skywatcher LP filter before its OK for general observing through the eyepiece, i seem to remember it caused a slight hue to the seen image. For imaging i use a CLS clip filter for my 450D

[jabberwocky]

They certainly block out the light, hold one up to your eye and look though it at a street light and they block all the cast light and just a dim glow from the light is visible but as for whether they improve the view through a scope or not I'm still undecided.

[umadog]

Your local street light and the orange pall that hangs over a city are two different things. If you have direct light shining on your observing site then you either need to get rid of it, shield it (possibly with a hood), or move site. LP filters (UHC and OIII) do work very well indeed on certain objects. They're pretty much mandatory on the large emission nebulae is Cygnus. Even from super dark skies, all those nebulae (Veil, N. America, Crescent). The ones in Sagittarius also respond well, particular the Eagle nebula. On other nebulae, particularly smaller ones, whether the filter will help depends on aperture. So there is debate on that front. But for the bigger nebulae: no debate.

[gooseholla]

I use LP filters. While the novelty of disappearing street lights never fails to amuse, for the sky, let us consider:

1. as people said, if it is glare coming in to your face or tube from a light, whilst it cuts that out, you won't see anything clearer.

2. for the skyglow, it depends how much there is. For heavy amounts they are about useless. For a little here and there, they actually work well.

3. They can help you see objects, but a standard LP filter, such as the £20 skywatcher one, isn't in reality going to bring out much more detail. I did a test in the winter with Orion nebula. Not huge differences, a bit. A darker patch in the garden and night adaption would do about the same for free.

4. The purple colour can be off putting! Everything looks a strange hue.

There are applications and scopes where it seems they are worth having. All you can really do is buy one or borrow one to try for yourself in your circumstances. All I will say is, I had a 1.25" and bought a 2" one when I upgraded eyepiece size...

[PorkyB]

I have just given up on my LP filter. It didn't improve the image at all, as far as I can tell. Tonight I was looking at doubles and with the filter in I couldn't see the mag 7.9 blue in Beta-Cep, with the filter out it was easy to see.

[Qualia]

I have just given up on my LP filter. It didn't improve the image at all, as far as I can tell. Tonight I was looking at doubles and with the filter in I couldn't see the mag 7.9 blue in Beta-Cep, with the filter out it was easy to see.

I don't know if this is really a help or whether what I'm going to say is misleading, but I think on all Light Pollution filters should be written:

** Warning - This Light Pollution Filter will not decrease all sky glow caused by artificial lights and will not enhance all deep sky objects. **

Okay, now the qualification, LP filters may decrease a significant amount of sky-glow but they will also decrease the surface-brightness of stars, clusters, globulars and galaxies. You see, stars, clusters, globulars and galaxies emit light waves including the same waves as street lights which the filter is happening to block. In effect, then, light pollution filters are diminishing the view of stars and galaxies.

However, nebulae (emission and planetary) emit a different kind of light wave than stars and galaxies and street lights, so this light goes straight through the filter. It follows that light pollution filters are designed to make nebulae stand out a little more.

Therefore, the term light pollution filter is a little misleading, if not a tad dishonest. They are not light pollution filters per se but nebula filters which are identified by the terms UHC and OII.

[cyborg421]

• contact local council , tell them the light is detracting for your enjoyment of your garden ,ask for a shield to fitted to the light , light pollution is a statutory nuicence ,and can be delt with by enviromental health
  

Does this apply to security lights as well?...

Simon

[NGC 1502]

Does this apply to security lights as well?...Simon

Hi Simon, other peoples security lights are tough to deal with. The perception by many is that it will deter wrongdoers and increase their security, so it's really hard for them to understand how their light could be a problem if it's lighting up your garden, and in their understanding increasing your security as no cost to you !!

Of course, astronomers don't see it that way at all. In fact, having a bright light shining down a garden may decrease security, by blinding onlookers to anyone lurking around. How would you spot a burglar at the back of a neighbours house, if you have a 500w light in your face.

It's best to tread carefully, and speak to the owner of the light, understand that they may have been a victim of crime and terrified of it happening again. Try to explain gently that astronomy is your passion and bright lights are a genuine problem to you. Yes I know, some people are have an impossible attitude, we've all met them. But it's worth a try, I've had some good responses from a neighbour at the back of me, he had a bright light on the outside of his conservatory, so I had a word and explained the issue. He said he didn't need that light, and took the bulb out (it was wired to come on with interior lights). When his son put a football through my fence, he put a note over to apologise and offered to pay, so I said no prob, thanks for sorting the light, and fixed the fence in 10 mins with wood from the shed.

Legal action is a last resort as it can start a war. There are no winners in a war, just losers and bigger losers.

Regards, Ed.

[RikM]

I don't know if this is really a help or whether what I'm going to say is misleading, but I think on all Light Pollution filters should be written:

** Warning - This Light Pollution Filter will not decrease all sky glow caused by artificial lights and will not enhance all deep sky objects. **

Okay, now the qualification, LP filters may decrease a significant amount of sky-glow but they will also decrease the surface-brightness of stars, clusters, globulars and galaxies. You see, stars, clusters, globulars and galaxies emit light waves including the same waves as street lights which the filter is happening to block. In effect, then, light pollution filters are diminishing the view of stars and galaxies.

However, nebulae (emission and planetary) emit a different kind of light wave than stars and galaxies and street lights, so this light goes straight through the filter. It follows that light pollution filters are designed to make nebulae stand out a little more.

Therefore, the term light pollution filter is a little misleading, if not a tad dishonest. They are not light pollution filters per se but nebula filters which are identified by the terms UHC and OII.

My understanding is that 'light pollution' filters let through most wavelengths but reduce the typical wavelengths associated with sodium and mercury lamps. 'Nebula' filters like UHC and Oiii reduce most wavelengths and only allow through the wavelengths associated with Ha, Hb, and/or Oiii emission.

I found that from my site, visually a 'light pollution' filter didn't really help too much with extended deep sky objects, but it does sometimes make details easier to pick out on planets and the moon. For imaging though, it makes a huge difference and a 2" one is a permanent feature on the inboard end of my coma corrector. UHC and Oiii filters do make a difference for observing nebulae but since they dim the view, they reduce the amount of magnification you can use. The veil nebula for instance, is completely invisible from my garden without the use of on Oiii filter.

I wouldn't have thought double star observation would benefit from any kind of filtration?