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Broadband/narrowband filters: whats the diff?

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#1 samm

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Posted 05 May 2021 - 10:14 PM

whats the purpose of these two type of filters? which wud be best for dealing with streetlight pollution?

thx for reading



#2 bobzeq25

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Posted 05 May 2021 - 10:34 PM

Visual use or imaging?   If imaging, mono camera or one shot color?


Edited by bobzeq25, 05 May 2021 - 10:36 PM.

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#3 havasman

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Posted 05 May 2021 - 11:29 PM

For visual the purpose of a nebula filter is to increase the apparent contrast of the emitting object against the background by filtering out the wavelengths that are not part of the emission spectrum of the object. Broadband filters are, by definition, less effective at this. More out-of-spectrum energy passes the filter and lessens the created apparent contrast.

For AP, IDK.


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#4 samm

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Posted 06 May 2021 - 12:07 AM

Visual use or imaging?   If imaging, mono camera or one shot color?

 

Imaging. One shot color, dslr



#5 bobzeq25

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Posted 06 May 2021 - 12:47 AM

True narrowband filters are designed for mono cameras, not recommended for one shot color.

 

There are pseudo narrowband filters called duo and tri band.  The LEnhance is a good example.  Specifically designed for one shot color.  They basically work on emission nebulae only.  For narrowband filters you need narrowband subjects.  Do an excellent job of reducing the effects of light pollution.  Below is an example of mine.  That's a pretty dim nebulae in light polluted skies, Bortle 7.

 

Broadband light polution filters are controversial.  I don't like them, don't use them.  They reduce signal as well as noise, distort color, make color processing hard.

 

What I use for reducing the effects of light pollution on broadband targets is gradient reduction in processing.  Not perfect, but works on all targets.  Astro Pixel Processor has an excellent GR tool, as do other astro specific processing programs.

 

To photograph emission nebulae well with a DSLR it needs to be modified, stock DSLRs reject most of the all important hydrogen alpha light.

 

Jellyfish, SH2-249 -small.jpg


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#6 jgraham

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Posted 06 May 2021 - 08:18 AM

Narrowband filters pass very narrowband of the spectrum that align with specific emission lines of emission nebula; primary H-b, O-III, H-a, and S-II. I have used the original Radian Triad filter with very good results and the Triad Ultra with excellent results.

Broadband imaging filters remove broad regions of the spectrum that are historically associated with light pollution from mercury and sodium vapor lamps, passing as much light as possible while suppressing skyglow. I have used the Hutech IDAS LPS2 and the Orion Imaging Skyglow Filter with very good results.

Broadband visual light pollution filters are similar, but they remove large sections of the spectrum, primarily in the red. These are generally not suitable for color imaging. I have used the Orion Skyglow filter with fair results for visual, poor results for color imaging.

The Orion Ultra Block passes a relatively narrowish band that passes the H-b and O-III lines associated with planetary nebula. I have experienced good results visually with this filter, fair-poor results imaging. The nebula are okayish, star colors are whacked.

Sooooo...

Modern multiband filters work well for narrowband imaging with a color camera.

Modern imaging skyglow filters continue to work fairly well from my Bortle 8 backyard.

Visual skyglow filters are generally not suitable for color imaging.

As light pollution shifts from vapor lamps to LEDs we will have to shift from using filters to custom white balances. These can be effective, but I'm still getting better results with my imaging skyglow filters. Multiband filters are not affected by the shift in light pollution, but these are only useful for emission nebula.

Food for thought.
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#7 EricSi

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Posted 09 May 2021 - 04:39 AM

I live in a very light polluted area right at the Seattle city limits, and I have never found that broadband filters help that much for visual observing. The filter that I use by far the most is the (narrowband) O III, which helps a lot with nebulae. But it may be different for photography....


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#8 bobzeq25

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Posted 09 May 2021 - 02:16 PM

I live in a very light polluted area right at the Seattle city limits, and I have never found that broadband filters help that much for visual observing. The filter that I use by far the most is the (narrowband) O III, which helps a lot with nebulae. But it may be different for photography....

Nope.  In imaging, filters (either narrowband or semi-narrowband, like duo or triband) work well on emission nebulae, everything else is marginal.  Post #5 applies.


Edited by bobzeq25, 09 May 2021 - 02:19 PM.



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