Light pollution/nebula filters

[Tribal-Wolf]

They're well packed aren't they Chris!

Almost welded in lol

[petermarknimmo]

So what would be the best type of filter for mercury or sodium lamps on a 114mm reflector?

[umadog]

It doesn't really work that way. It works the other way around: they aren't designed to block street lights, they're designed to pass emission bands from nebulae. Emission nebulae fluoresce because the atoms they contain are excited by nearby radiation sources, such as stars. In contrast to stars, which are broad band emitters, nebulae emit light at a narrow range of wavelengths. Light pollution filters leverage this fact to increase contrast by passing the emission bands whilst blocking almost everything else. This contrast boost holds in both dark skies and light polluted skies, meaning that "light pollution filter" is somewhat of a misnomer.

A UHC filter is probably the best choice to start with. Since the filters block a lot of light the view will be dimmer. Consequently, your highest useful power per inch goes down. Expect to get between about 5x to 10x per inch. So somewhere between 20x to 40x. Don't therefore look to the filters helping you with objects that require higher powers, such as planetary nebulae. You'll get better views of those without a filter, I would bet. Instead, the filter will be useful for large emission nebulae which look good at low power.

[rory]

umadog, thats very well explained, thanks.

[swamp thing]

Umadogs pretty much covered it there.

Just thought I'd add. Remember no nebula filters work on reflection nebulae as they reflect starlight from right accross the spectrum and therefore the filter blocks light from them.

Regards Steve

[sologuitarist61]

This really does work well:

First Light Optics - Skywatcher Light Pollution Filter

Yes I have one of these and it enhances the subject very nicely.

[RikM]

Umadogs pretty much covered it there.

Just thought I'd add. Remember no nebula filters work on reflection nebulae as they reflect starlight from right accross the spectrum and therefore the filter blocks light from them.

Regards Steve

They don't really help too much with galaxies either, being composed mainly of stars.

I thought the more subtle dedicated light pollution suppression or Moon and skyglow filters (SkyWatcher LPR, Baader Neodymium, Astronomic CLS) did work by blocking sodium and mercury emissions letting through a wider pass band of wavelengths. Ha and Oiii filters are narrow band, only letting through those emission lines, and a UHC is a half-way house letting through Ha+Hb+Oiii.

[sologuitarist61]

They don't really help too much with galaxies either, being composed mainly of stars.

I thought the more subtle dedicated light pollution suppression or Moon and skyglow filters (SkyWatcher LPR, Baader Neodymium, Astronomic CLS) did work by blocking sodium and mercury emissions letting through a wider pass band of wavelengths. Ha and Oiii filters are narrow band, only letting through those emission lines, and a UHC is a half-way house letting through Ha+Hb+Oiii.

That was my understanding as well.

[Stu]

Going back to the OIII comments, I do occasionally use one in a 4" frac from dark sites. It has allowed me to view the Veil through this scope using 31t5 nagler. It's not bright but definitely visible.

In general I think the UHC is better in smaller scopes as it is less extreme. The OIII is great in a 10", no problems.

Stu

[swamp thing]

They don't really help too much with galaxies either, being composed mainly of stars.

They can help with spotting H11 regions in other galaxies.

M33 has many very bright H11 regions that an O-III helps with, so indirectly it is helping you with the Galaxy.

But on the whole you are right they won't help with Galaxies.

[sologuitarist61]

Just ordered a Neodynium filter, so am hoping it is better than my Skywatcher LP filter (though that ain't bad!!)

[JamesM]

Chris, I have use one of those Baader Neodymium filters for some time now and they do work but I certainly wouldn't claim them to be a magic bullet where light pollution is concerned, although every little helps. The real advantage that I have noticed is with regards to improving contrast, particularly on Saturn and Jupiter. I also chose this one over the Skywatcher version because it has the hardened finish which protects the surface when cleaning. Have mine screwed onto my diagonal all the time.

Clear skies soon and hope you enjoy it!

James

[dph1nm]

Just ordered a Neodynium filter, so am hoping it is better than my Skywatcher LP filter

I see to remember that when the Skywatchers first appeared, rumour had it that they were identical to the Neodynium filters (just cheaper!). I have no idea if this is true though.

NigelM

[RikM]

I had a look through both at a star party and couldn't see any difference so I bought the SkyWatcher. There is a photo trial thread somewhere on here and they don't look much different in images either.

[Tribal-Wolf]

I think if I already had the skywatcher filter I wouldn't fork out for the Baader, I went for the baader purely because I had been recommended it by more people.