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Narowband filter bandwidth

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#1 txo

txo

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Posted 26 June 2019 - 05:20 AM

Hi there, 

 

What is real world difference between say 13nm, 6nm, 4nm Ha filter for astrophotography?

 

Thank you

t.

 

 



#2 happylimpet

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Posted 26 June 2019 - 05:37 AM

Narrower bandwidth (small FWHM in nm) means darker background, so better in light polluted skies. Fainter stars. Less ability to image HII regions in redshifted galaxies. More cash spent.


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#3 HydrogenAlpha

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Posted 26 June 2019 - 06:56 AM

I live in a Bortle 8/9 zone, and I use a 7nm HA. I feel that it is sufficient for my needs, and the very narrow bandpasses are reserved for the much fainter OIII and HA, 

 

Also, note that very narrow bandpasses has issues with fast systems. There is a bandpass shift at oblique incidence angles, so you probably wouldn't want to use a 4nm filter (especially one without a bandpass preshift) with an f/3 system. 



#4 NuclearRoy

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Posted 27 June 2019 - 09:52 AM

+1 on CASH. Very narrow filters are very expensive to make.

I'm using 7nm with an f/4 system (including a ASI1600MM-Pro) and getting what I think are good results so far, mostly with H-alpha to this point. I just did my first H-alpha + O-III last week.

That said, I'm new here so YMMV.




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