Light Pollution Filters - Recommendations

[Toxophilus]

I'm in a really badly light polluted area, often the only way of seeing something is to try and image it with a 30 or more second exposure and actually viewing it directly is almost impossible at the moment hopefully things will improve in the winter. However when I do try to do an image, I often end up with the image being a lovely grey and a faint outline of the target buried in there somewhere, which I have to stack a few images and then manipulate to cut out the LP and pull the object out. This gives me some OK images  but nothing fantastic. Are there any LP filters that anyone can recommend. I have used the skywatcher one and that helps a little but it just does not seem to be aggressive enough. Unless of course there is some other technique that anyone can suggest for dealing with LP.

Thanks for your help/suggestions

Mark

[Andy Mitchell]

Depends a lot on what things you want to look at and on the colour of the light pollution in your area. If its mostly the orange low pressure sodium things are easy, if its all pure white LED/CFL things are, to say the least, challenging.

If the filter you have looks like slightly tinted glass, its probably neodymium glass that does a pretty good job of absorbing some of the most common problems, e.g. the orange from low pressure sodium lamps. The transmission curve is a bit all over the place mind. If you spend more you can get interference filters (aka dichoric) that acts as a mirror to unwanted frequencies. They have more ideal filter characteristics and can be produced to let through as much or as little of the spectrum as the designer wants.

Can you describe your light pollution sources and what you want to look at?

[Toxophilus]

Hi Andy, 

I think it's mainly low pressure sodium light in my area (that horrible yellow to orange glow). I'm mainly galaxy hunting at the moment.

Mark

[Toxophilus]

Oh BTW, I don't mind spending a bit on a better filter, but I don't want to spend a load on something that is just not going to work.

[Andy Mitchell]

Something like the Astronomik CLS or CLS-CCD filters would be good. The CCD version costs more and filters out infared as well. For standard unmodified DSLRs either version is fine, for astronomy dedicated cameras you need the IR cut function.

Other brands are available, and some may be better value as Astronomik are expensive. I've used quite a few of their other filters with good results.

[rharrison]

I use a 2 inch Baader UHC s, doubles the possible exposure times and doesn't mess up the colours too badly, I did have a cheaper one off ebay that just made everything green.

[Toxophilus]

Something like the Astronomik CLS or CLS-CCD filters would be good. The CCD version costs more and filters out infared as well. For standard unmodified DSLRs either version is fine, for astronomy dedicated cameras you need the IR cut function.

Other brands are available, and some may be better value as Astronomik are expensive. I've used quite a few of their other filters with good results.

Cheers Andy, I'm using an Atik 314L+ (my main camera) and a ZWO ASI120mc. So I will look at the IR cut version.

[Toxophilus]

I use a 2 inch Baader UHC s, doubles the possible exposure times and doesn't mess up the colours too badly, I did have a cheaper one off ebay that just made everything green.

Yes one of the filters that I tried made everything blue. I will have a look at the Baader. Its colour casting that I would like to keep to a minimum.

[laser_jock99]

I sometimes use the Hutech IDAS D1 Filter which seems to work well on emission nebulae:

M42 12x 120s 6" F4 Newtonian with IDAS D1

Same set up with no filter

[silios]

The baader UHC-S is awesome for what it is : narrowband filters combined to a single one and it works wonders in light polluted cities for nebulas but that's pretty much it, as far as i have tested it .

For all around use you might want to consider the The Hutech IDAS LPS -P2 which is highly appraised by many astrophotographers.

There is a nice article outlining the  differences between various LP filters (its Hungarian but the images are speaking for themselves!) http://www.pleiades.hu/tesztek_csillagaszat/melyeg_szurok_1.html

[johnrt]

+1 for the Hutech IDAS.

[Toxophilus]

Cheers Silios. I will have a look at that article.

[Andy Mitchell]

UHC filters are a better match for emission nebulas like M42, horsehead etc. Downside is they remove a lot more frequencies so not so good for other things. One thing to watch out for is that while most UHC filters let through the key bits of red (e.g. Ha) and blue-green (e.g OIII, Hb) some vary from this formula. Skywatcher did one that doesn't let through any red and you probably dont want that.

[dph1nm]

For imaging I think people

1) overestimate the effect of LP filters.

2) don't realise how much you can get out of light polluted data anyway

Yes they knock out some sodium lines, but they also take a chunk of  light away from the object itself, and I have seen some filters where the second effect outweighs the improvement given by the first!

I do have the Skywatcher one - it is fine, and I wouldn't expect anything else to do substantially better.

NigelM

[Toxophilus]

For imaging I think people

1) overestimate the effect of LP filters.

2) don't realise how much you can get out of light polluted data anyway

Yes they knock out some sodium lines, but they also take a chunk of  light away from the object itself, and I have seen some filters where the second effect outweighs the improvement given by the first!

I do have the Skywatcher one - it is fine, and I wouldn't expect anything else to do substantially better.

NigelM

You are right, and I'm not expecting a light pollution filter to do miracles, but just give me a little more contrast so that it makes it a bit easier to try to pull the object out from all the noise from the pollution.

I must admit I forgot to put my skywatcher LP filter in the other night and the difference in the data was noticeable.

[Snaxmuppet]

This is a particularly interesting thread for me because I am about to buy a new imaging set up and am struggling to come to terms with paying £150 for a filter when I really am not certain just how much it will help. If it works then £150 is worth paying but at the moment I am a bit anxious.

Most of the light locally is white/LED type lighting but not far away (4 miles) is Plymouth with a mix including the sodium yellow.

I am tempted to get nothing for now and see what kind of results I can get from unfiltered data and only get one if I am dissatisfied with the results.

I was thinking that if I did get a LP filter I'd do well to get the IDAS P2. I will be shooting nebulae and galaxies mostly I expect.

[Snaxmuppet]

You are right, and I'm not expecting a light pollution filter to do miracles, but just give me a little more contrast so that it makes it a bit easier to try to pull the object out from all the noise from the pollution.

I must admit I forgot to put my skywatcher LP filter in the other night and the difference in the data was noticeable.

Perhaps then I could get a SW one as they are much cheaper and at least I would have something?

[Toxophilus]

Perhaps then I could get a SW one as they are much cheaper and at least I would have something?

You could look at trying that one as its fairly cheep and if it does not have the desired effect then you have not lost too much. At the moment the best option looks like the IDAS P2 as it seems to be very specific on the wavelengths that its cutting out and therefore letting as much light through as possible. £150 is a lot of money to spend on something that you don't know will do the trick. Its just a shame there is not a filter library available where you could pay a small a mount to rent out a filter for a week or so to try. Unless of course someone knows about such a service...

[johnrt]

You could look at trying that one as its fairly cheep and if it does not have the desired effect then you have not lost too much. At the moment the best option looks like the IDAS P2 as it seems to be very specific on the wavelengths that its cutting out and therefore letting as much light through as possible. £150 is a lot of money to spend on something that you don't know will do the trick. Its just a shame there is not a filter library available where you could pay a small a mount to rent out a filter for a week or so to try. Unless of course someone knows about such a service...

Buy from First Light Optics

It would, but it would be difficult for someone to devise a 'definitive' test because a light pollution suppression filter's success depend to a large extent on how well it matches your local light pollution. This is why user reviews of light pollution suppression filters vary so much in their conclusion. If it is a good match you will think it astounding, if not you will be wondering what all the fuss is about. This is why, with all our light pollution filters, we offer a full refund if you find it is not effective with your sky

[Toxophilus]

Cheers johnrt,

I was going to use FLO anyway as I have always had good service from them, but I did not know about that offer. You can't say fairer than that really. 

[pipnina]

This is a particularly interesting thread for me because I am about to buy a new imaging set up and am struggling to come to terms with paying £150 for a filter when I really am not certain just how much it will help. If it works then £150 is worth paying but at the moment I am a bit anxious.

Most of the light locally is white/LED type lighting but not far away (4 miles) is Plymouth with a mix including the sodium yellow.

I am tempted to get nothing for now and see what kind of results I can get from unfiltered data and only get one if I am dissatisfied with the results.

I was thinking that if I did get a LP filter I'd do well to get the IDAS P2. I will be shooting nebulae and galaxies mostly I expect.

Plymouth is almost entirely low pressure sodium. There are a lot of LEDs springing up but I wouldn't worry about them- if anything they're a good thing! (they don't send much light upwards compared to the sodium lamps, although they emit at just about every single visible frequency so their reduced LP is impossible to filter.

[Dave In Vermont]

Here's a link to an excellent article showing which filters is best for various deep-sky objects:

http://www.prairieastronomyclub.org/resources/by-dave-knisely/filter-performance-comparisons-for-some-common-nebulae/

Everyone interested in filters should have one. I have one on my wall. And 36 filters in my cases.

An Avowed Filter-Nut,

Dave

[ronin]

The problem of the LED's is they may be directing more of the light downwards, but you are pointing a scope upwards. That downward going light therefore still ends up in the scope.

Think the problem is that we use the term "light pollution" and maybe it is wrong, or it is too general and not specific enough.

Used to be meant that if you were 10 miles away there was a yellow glow over whatever town.

That however is when you are outside of the place looking at or towards it.

In many instances here we are sat inside looking out, not sat outside looking in.

Our concern in that situation is the ambient light.

[Toxophilus]

Here's a link to an excellent article showing which filters is best for various deep-sky objects:

http://www.prairieastronomyclub.org/resources/by-dave-knisely/filter-performance-comparisons-for-some-common-nebulae/

Everyone interested in filters should have one. I have one on my wall. And 36 filters in my cases.

An Avowed Filter-Nut,

Dave

That's quite a long list. I will have a read of it later when I get an opportunity.

[pipnina]

The problem of the LED's is they may be directing more of the light downwards, but you are pointing a scope upwards. That downward going light therefore still ends up in the scope.

Think the problem is that we use the term "light pollution" and maybe it is wrong, or it is too general and not specific enough.

Used to be meant that if you were 10 miles away there was a yellow glow over whatever town.

That however is when you are outside of the place looking at or towards it.

In many instances here we are sat inside looking out, not sat outside looking in.

Our concern in that situation is the ambient light.

But getting to a place where streetlamps aren't visible is much easier than getting away from sky glow. Sky glow is visible for more than 20 miles if it's the centre of a bright city, but street lamps (esp. the LED ones) you might have to travel a few hundred metres or go to the nearest beach/national park.