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Light polution Filter for Lum layer in LRGB

astrophotography filters LP
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#1 happydaddy

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Posted 20 January 2021 - 05:18 PM

Hi, 

let me start by saying i am moving from color to mono camera.

I will start with LRGB + Ha filter

I am leaving in a light polluted area class 7.

With my color camera, i am using optlong l-pro which is working well.

For nebula, i plan to use Ha filter for lum but i am wondering what to use for the galaxies.

I would continue to use the l-pro but i will use astronomik deepsky filter for RGB and i was told to use parafocal filters.

I looked at the CLS-CCD and the UHC but one seems too weak and the other too selective...

 

So my questions are the following :

what filter would you recommend for L layer  in a mix type of light polution quite severe for galaxy imaging for LRGB ?

would you give priority to parafocal filters over best polution filter option in a filterwheel ?

 

any other advise ?

 

Thx a lot community !!!

 



#2 bobzeq25

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Posted 20 January 2021 - 06:15 PM

I'm no fan of LP filters, especially for galaxies, which emit light across the whole spectrum.  You tend to lose too much signal.

 

So, less is more.  I suggest a Baader neodymium which is very weak, but useful.  In this case, weak is good.

 

Good read.  Some very serious and experienced imagers here.  I also posted.  <smile>

 

https://www.cloudyni...-the-answer-is/

 

What does work is gradient reduction in processing.  Rather than whack out the spectrum with a meat axe, it looks for the characteristic spatial signature of light pollution, strong at the horizon, weak overhead.  And then sophisticated algorithms subtract it out.  Not perfectly, but it doesn't remove much, if any, signal. 

 

Bottom line.  Serious imagers use GR on everything.  Some additionally add a broadband LP filter, some don't.  Most of those who do use them on emission nebulae, only.

 

Most astro specific processing programs have GR tools.  I recommend Astro Pixel Processor.

 

Below is an image of Andromeda from Bortle 7.  DSLR.  No (not so) magic LP filters used.  Spent an hour getting GR right.  A photographer friend of mine playfully accused me of faking it.  He wasn't serious, just complimenting for what I'd done in skies just like his own.

 

m31final_small.jpg


Edited by bobzeq25, 20 January 2021 - 06:24 PM.

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#3 happydaddy

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Posted 21 January 2021 - 06:20 AM

Thx a lot for your reply, and your nice Andromeda photo gives me hope. I am indeed using PixInsight to reduce impact of the light pollution. The l-pro has been for me very useful but for nebula. You confirm what i thought that bot l-pro and UHC are clearly not good.

I did the reading of your previous post, vert interesting indeed. I might start with the default L filter coming with the LRGB set and see. Thx a lot !!!


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#4 bobzeq25

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Posted 21 January 2021 - 12:27 PM

Tips.  I find ABE to work almost always, and it's much easier than DBE.  It's also harder to mess up.

 

Presumably you've already realized it's necessary to change the default setting in "Correction", which is "None" (there's actually a somewhat obscure reason for that) to "Subtraction".

 

The other setting to mess around with in ABE is Interpolation.  The default is 4, lower values, including 1, may be better.


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#5 happydaddy

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Posted 21 January 2021 - 02:57 PM

Hi,

i am usually trying DBE, and i spend a hell lot of time in order to get a decent result... i ll follow your tip and get back to ABE.

When it comes to correction, i just saw a tuto where the guy explained he was usually doing twice ABE, considreing that division was taking care of the gradient more at the edge (not vigneting but alike in term of shape) while substraction was some residual funny shape gradient ( or may be it was the opposite. Do you have any comment on that ?



#6 bobzeq25

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Posted 21 January 2021 - 06:26 PM

Hi,

i am usually trying DBE, and i spend a hell lot of time in order to get a decent result... i ll follow your tip and get back to ABE.

When it comes to correction, i just saw a tuto where the guy explained he was usually doing twice ABE, considreing that division was taking care of the gradient more at the edge (not vigneting but alike in term of shape) while substraction was some residual funny shape gradient ( or may be it was the opposite. Do you have any comment on that ?

Could work.  I've done two steps of ABE or both ABE and DBE (in either order) but always use subtraction.  I'll try one iteration as division.

 

Sometime.  <smile>
 


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