# Filter claims to reduce light pollution for astro



## YellowJersey (Dec 14, 2016)

Saw this over at Peta Pixel. It's a filter that claims to help cut out light pollution while not impacting your exposure of the stars. 

http://petapixel.com/2016/12/14/purenight-filter-cuts-light-pollution-better-night-sky-photos/


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## scyrene (Dec 14, 2016)

There are other members here who are much more expert than me, but I will say this: light pollution filters for astronomy and astrophotography have been around for a long time. They vary by price and reputation. I have used them and they can be useful if you're doing work in urban and suburban areas on fainter targets, and have a low-ish budget. However a few issues are worth bearing in mind...

Light pollution varies. It used to be easier as a lot of street lights were sodium-based, and that's a fairly narrowband type of (garish yellow-orange) light. Increasingly, it is broadband - white LEDs are taking over, which means it's much harder to selectively filter out. Second, if you're photographing stars (constellations, globular clusters, and the brighter galaxies), you don't really need an LP filter (unless, e.g. you're going for hydrogen-rich nebulae in spiral galaxies etc). Third, judging by that article, the guy was already in a fairly dark sky site. I've almost never had such rich images of the Milky Way, even in the darkest places I've been (I've never visited true dark sky sites). The before and after images looked more like a white balance adjustment had been done. I think a better example would be an urban site - and it makes me question how good this filter really is.

Ultimately, if it's something you want to pursue, you need two things: a mount that can track the sky and get long exposures, and narrowband filters for the wavelengths emitted by your subjects, e.g. hydrogen alpha for red nebulae. Some would add an astro cam or modified DSLR that has its IR filter removed. If you want to do landscape work (e.g. mountains with the Milky Way behind), there's no substitute for travelling to somewhere remote and as dark as possible.


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## East Wind Photography (Dec 14, 2016)

I only see a color shift and if he had to bump exposure by .7 then it also is reducing the total amount of light. I dont see any enhancement of the nebulas in the milky way.

I done see enough gain here to make it worth the expense.


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## ahsanford (Dec 14, 2016)

I am a rank amateur at astro, but I know the name Lonely Speck. It's a helpful website to get you started in what I find to be a very technical arena of photography.

I am surprised to see a group in the blog/photo community/tutorial game is actually pushing a _product_. Good luck to them, I say.

- A


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## JMZawodny (Dec 15, 2016)

I use an IDAS LPS-P2 (http://www.sciencecenter.net/hutech/idas/lps.htm) and it does a fine job suppressing Mercury vapor lamps and Sodium lamps. These are interference filters though and the bandpass shifts in wavelength with angle of incidence, so they do not work well with wide angle or even moderate angle lenses. They are limited to telephoto lens use only.


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## JMZawodny (Dec 15, 2016)

Seems like they already exist.

http://www.lonelyspeck.com/hoya-intensifier-review-an-affordable-light-pollution-filter-for-astrophotography/


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## niels123 (Dec 15, 2016)

I too am an absolute amateur in astrophotography and occasionaly I'd like to create some landscape-like images with the sky and stars included. I don't have any intention in getting a tracking, I even prefer the star trail effect ;D

However, I did buy the "clear sky" (CLS) clip-in filter from astronomik.com. Their filters are amazing because they clip inside the mirrorbox of your dslr. They have two sizes: one for APS-C and one for FullFrame. With FullFrame you can't use the mirror anymore (it remains flipped-up with the filter in place) and your limited to liveview (but that's not an issue at all when shooting stars. With APS-C the mirror function is still available when the filter is clipped in place.

The advantage is that you can literally use every lens with just one filter, including fisheye, mirror lenses, a 600mm with no front filter thread etc.

I have a 6D which is modified for IR photography and they sell several IR filters in clip-in format as well.

Full frame clip in video


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## Don Haines (Dec 15, 2016)

Keep in mind that the advertising for the filter will show the best case results, and that typically things will not work as well as advertised.....


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## Fatalv (Dec 15, 2016)

East Wind Photography said:


> I only see a color shift and if he had to bump exposure by .7 then it also is reducing the total amount of light. I dont see any enhancement of the nebulas in the milky way.
> 
> I done see enough gain here to make it worth the expense.



+1 It looks more like a color shift than anything else. 

At $220 I'd rather spend the money to take a drive to the dark park and fix any color shift in post


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## Djaaf (Dec 15, 2016)

Fatalv said:


> +1 It looks more like a color shift than anything else.
> 
> At $220 I'd rather spend the money to take a drive to the dark park and fix any color shift in post



It's not "just" a colour shift, it does cut off some frequencies generally associated with urban light pollution. 
But ultimately you're right : it's generally not a very good investment and the best way to get good result is still to go out in the dark.  

If you're really into astronomy shots in a urban settings, you'll have to use the Hubble method and go for very narrow-band filters (H-Alpha 6nm, OIII and SO2 mostly). Those do effectively cut off pretty much all frequencies except for a very narrow band. But post-production will be a real pain.  

Djaaf.


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## LesC (Dec 22, 2016)

*Light Pollution Reduction Filter*

This looks interesting, if a little expensive: http://www.lonelyspeck.com/purenight/

Wonder how effective it may be in reality?


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## mnclayshooter (Dec 22, 2016)

*Re: Light Pollution Reduction Filter*

There's already a discussion started: 

http://www.canonrumors.com/forum/index.php?topic=31494.msg640907


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## IglooEater (Dec 23, 2016)

I'd like to hear jrista's take on this. It looks like a colour shift as folks have said. What strikes me about it is the possibility of getting city lights AND the Milky Way in the same shot- if might prevent the city from being so blown out as to be beyond the reach of PP, while still preserving some detail of the MW.


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