Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Narrowband filters

  • Please log in to reply
13 replies to this topic

#1 shrimpus

shrimpus

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 20 Jul 2019

Posted 20 July 2019 - 03:50 PM

I really dont understand narrowband filters. At some point in the future, I am going to buy a nice ZWO camera for DSO photography. But I live in a light polluted suburb, so I would need narrowband filters. I know there are 3 types, but I dont know when I would need to use each, or what each of them do.

 

Thanks



#2 havasman

havasman

    Cosmos

  • ****-
  • Posts: 9613
  • Joined: 04 Aug 2013
  • Loc: Dallas, Texas

Posted 20 July 2019 - 04:15 PM

https://www.prairiea...ep-sky-objects/

https://www.prairiea...common-nebulae/

 

Those are probably the best intro articles on the subject.

 

Google narrowband UHC, cloudy nights and narrowband O-III, cloudy nights and H-Beta filter, cloudy nights​ and you will get more leads to CN articles than you'll read.

 

Narrowband filters are extremely useful to the visual observer who wants to increase the apparent contract of a nebular object against the field. The filter's passband should be matched to the emission band of the nebula.


Edited by havasman, 20 July 2019 - 04:16 PM.

  • shrimpus likes this

#3 shrimpus

shrimpus

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 20 Jul 2019

Posted 20 July 2019 - 04:17 PM

https://www.prairiea...ep-sky-objects/

https://www.prairiea...common-nebulae/

 

Those are probably the best intro articles on the subject.

 

Google narrowband UHC, cloudy nights and narrowband O-III, cloudy nights and H-Beta filter, cloudy nights​ and you will get more leads to CN articles than you'll read.

 

Narrowband filters are extremely useful to the visual observer who wants to increase the apparent contract of a nebular object against the field. The filter's passband should be matched to the emission band of the nebula.

What does emission band mean?



#4 havasman

havasman

    Cosmos

  • ****-
  • Posts: 9613
  • Joined: 04 Aug 2013
  • Loc: Dallas, Texas

Posted 20 July 2019 - 04:34 PM

The articles explain it better than I will but when an atom is excited by radiation in space and an electron jumps valence for a bit and the atom becomes ionized it is unstable. The electron hopping back to its home orbit emits a photon at a frequency. High enough concentrations of ionized atoms in space emit enough photons to be detected here and we see a nebula. The frequency of those photons can be described. That is the emission band. Hydrogen, oxygen, sulphur and other elements emit at different frequencies and those frequencies allow science to describe MANY cosmological phenomena. The frequencies detected from a particular nebula are often described as its emission band. Most visible nebulae have relatively narrow emission bands in the visual spectrum. So a filter constructed with a narrow passband matched to that emission band will be effective at increasing the apparent contrast of the nebular object against its field by darkening everything in the field that is NOT in the emission band.

 

Also - https://en.wikipedia...ssion_spectrum 

and - https://www.quora.co...spectrum-unique


Edited by havasman, 20 July 2019 - 08:51 PM.

  • Simon B, Barlowbill, OldManSky and 1 other like this

#5 havasman

havasman

    Cosmos

  • ****-
  • Posts: 9613
  • Joined: 04 Aug 2013
  • Loc: Dallas, Texas

Posted 20 July 2019 - 04:45 PM

Also - WELCOME TO THE FORUMS!!


  • shrimpus likes this

#6 StarBurger

StarBurger

    Mariner 2

  • -----
  • Posts: 259
  • Joined: 06 Mar 2018
  • Loc: North Country NY

Posted 20 July 2019 - 04:47 PM

The various chemical elements in emission nebulae (e.g oxygen, hydrogen, sulfur etc.) give off light in particular narrow bands of the spectrum, typically just nanometers in width when stimulated by heat or other high energy processes.

Using, say, a narrow band Ha filter will only allow the light emitted by the Hydrogen alpha excitation to pass through.

H alpha emission is in the deep red area of the spectrum.

Many nebulae are particularly strong in Ha e.g the North American neb.

Other nebulae e.g. planetaries (M 57, M 27) are stronger in O III in the green region of the spectrum.

The great advantage of such narrow band filters is that they block the "unwanted"  light from artificial sources (light pollution!) which are almost always broadband sources except for sodium and mercury generally which are blocked by H, O III and S filters.

Using narrow bands means that you are seeing only what comes down from the sky in the narrow bands particular to the filter used and the emission strengths of the nebula

One might think that a lot of light is being missed by such filtration but largely most of the light from nebulae is O, H and S.


  • PirateMike and Barlowbill like this

#7 shrimpus

shrimpus

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 20 Jul 2019

Posted 21 July 2019 - 04:24 PM

The various chemical elements in emission nebulae (e.g oxygen, hydrogen, sulfur etc.) give off light in particular narrow bands of the spectrum, typically just nanometers in width when stimulated by heat or other high energy processes.

Using, say, a narrow band Ha filter will only allow the light emitted by the Hydrogen alpha excitation to pass through.

H alpha emission is in the deep red area of the spectrum.

Many nebulae are particularly strong in Ha e.g the North American neb.

Other nebulae e.g. planetaries (M 57, M 27) are stronger in O III in the green region of the spectrum.

The great advantage of such narrow band filters is that they block the "unwanted"  light from artificial sources (light pollution!) which are almost always broadband sources except for sodium and mercury generally which are blocked by H, O III and S filters.

Using narrow bands means that you are seeing only what comes down from the sky in the narrow bands particular to the filter used and the emission strengths of the nebula

One might think that a lot of light is being missed by such filtration but largely most of the light from nebulae is O, H and S.

so would you use a different narrowband for different nebulae?



#8 rkelley8493

rkelley8493

    Viking 1

  • *****
  • Posts: 814
  • Joined: 19 Jan 2019
  • Loc: Southeast USA

Posted 21 July 2019 - 11:47 PM

so would you use a different narrowband for different nebulae?

Check out this detailed report on how the 4 types of filters [Light Pollution/Deep Sky, UHC, O-III, & H-beta] performed on just about every nebula in the night sky.

 

https://www.prairiea...common-nebulae/


  • shrimpus likes this

#9 shrimpus

shrimpus

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 20 Jul 2019

Posted 22 July 2019 - 07:25 AM

Check out this detailed report on how the 4 types of filters [Light Pollution/Deep Sky, UHC, O-III, & H-beta] performed on just about every nebula in the night sky.

 

https://www.prairiea...common-nebulae/

how well do they work on clusters and galaxies?

 

also what is the best one for deep sky astrophotography? I thought it might be UHC, but apparently it is best for observing, and that isn't my main goal.


Edited by shrimpus, 22 July 2019 - 08:08 AM.


#10 rkelley8493

rkelley8493

    Viking 1

  • *****
  • Posts: 814
  • Joined: 19 Jan 2019
  • Loc: Southeast USA

Posted 22 July 2019 - 01:22 PM

how well do they work on clusters and galaxies?

 

also what is the best one for deep sky astrophotography? I thought it might be UHC, but apparently it is best for observing, and that isn't my main goal.

The Baader UHC-S filter works pretty well as a "Deep Sky" filter. It's more broadband than a true UHC filter [like Lumicon & Astronomik]. Broadband means it lets a broader part of the visible light spectrum pass thru the filter. Narrowband nebula filters typically don't work well on galaxies. 

I can't say how well they work for astrophotography.. I'm a visual observer. However, there are a lot of knowledgeable people here on Cloudy Nights. I'm sure someone else can comment on what filters are best for AP. Just spit-balling here, but I think something like a filter wheel with Luminance, Red, Green, Blue would be best for AP. If you can only get one, maybe something like the Baader/Celestron [same filter, different decals] UHC-S would be pretty good at filtering light pollution & sky glow. I found this photo on Stargazer's Lounge:

 

uhc.jpg



#11 havasman

havasman

    Cosmos

  • ****-
  • Posts: 9613
  • Joined: 04 Aug 2013
  • Loc: Dallas, Texas

Posted 22 July 2019 - 01:43 PM

so would you use a different narrowband for different nebulae?

Haven't read the articles, have you?

 

 

how well do they work on clusters and galaxies?

 

also what is the best one for deep sky astrophotography? I thought it might be UHC, but apparently it is best for observing, and that isn't my main goal.

You might want to post your AP question in the beginners AP section of the forums and you'll likely get better info from experienced AP aficionados.


  • rkelley8493 likes this

#12 HydrogenAlpha

HydrogenAlpha

    Ranger 4

  • -----
  • Posts: 313
  • Joined: 02 Oct 2014
  • Loc: Singapore

Posted 25 July 2019 - 05:50 AM

By 3 types, do you mean HA, SII and OIII? Or do you mean broadband, UHC, and emission line? 

 

I don't tend to consider broadband and UHC filters as "narrowband", so I assume you're referring to emission line filters, which mainly come in the HA, SII and OIII passbands. 

 

Also, I'm assuming you don't understand electron transitions or the EM spectrum (but these are fundamental concepts, so read up on those), so I'll leave the theory out of it. 

 

In practical terms, you can only use narrowband filters on emission nebulae. This means that they will NOT work on galaxies, stars, star clusters, or reflection/absorption nebulae. Also, they need to be used with monochrome cameras (or contend with gross inefficiency). 

 

The purpose of having 3 filters is to be able to generate a (false) colour image. Normal colour images are made up of 3 parts (here on referred to as 'channels'): a red channel, a green channel, and a blue channel. Normal colour cameras achieve this by using coloured filters on the pixels. However, since we are not using typical red, green and blue filters, we need to assign the images from the HA, SII and OIII filters into these colour channels to create a coloured image. The resulting colour image does not represent the actual colours of the object (at least in the way that the human eye would see if it were much more sensitive), but it is scientifically valuable for identifying the abundance of various elements. For astrophotography, this tends to create rather pleasing colour images. 



#13 HydrogenAlpha

HydrogenAlpha

    Ranger 4

  • -----
  • Posts: 313
  • Joined: 02 Oct 2014
  • Loc: Singapore

Posted 25 July 2019 - 05:51 AM

btw, make sure you don't mix up the visual and imaging filters as they have different passbands. Also, do not get H-beta, as it is a visual-only filter. You'd be wasting your time if you bought one for imaging. 



#14 Mike W.

Mike W.

    Vanguard

  • *****
  • Posts: 2220
  • Joined: 23 Dec 2016
  • Loc: Washington State

Posted 25 July 2019 - 06:56 AM

Here's a link to a site I use to compare visual filters, the graph displays the filter selected from the side bar to the right of the graph, toggle the filter by clicking on the box next to it.

 

https://searchlight....9d-153d7e7c0eb8

 

You can select several filters and their light pass will stack on top of each other.

 

When first entering the site it will boot with the 3 main narrow bands represented in color on the graph.

 

Take your time, you'll get the hang of it.

 

 

 

One of these days I'm going to send all my filters to this guy so he can add them to the selection base.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics