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M31 with OSC & LP filter

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#1 neaptide

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Posted 24 September 2020 - 10:11 PM

Here's 6 hours on M31 using ASI294mc Pro with an Idas LPS D1 filter. I tried without using the LP filter but this target is right above the LED streetlight across the street and I was getting a very strong gradient. The D1 filter absolutely helped but I wonder if there are any better options out there.

 

AT72ed ii / .8x reducer

CGX

ASI294mc Pro

Idas LPS D1 filter

Sharpcap3.2, Stellarium Scope, PHD2

DSS, StarTools, GIMP, Paint.net

 

365 X 60"  Gain 120  -10c

 

C&C Welcome

 

M31 IDAS LPS D1 StarTools GIMP.jpg


Edited by neaptide, 24 September 2020 - 10:28 PM.

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#2 bobzeq25

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Posted 24 September 2020 - 10:54 PM

The better option is gradient reduction in processing.  Details.

 

No filter will work well for LED lights and Andromeda.  "Light pollution" filters don't magically filter out light pollution.  They whack out hunks of the spectrum, hoping that what they whack is mostly light pollution, and what they pass contains most of the signal.  That can work decently for emission nebulae, and metal vapor lights.  By the time you get to LEDs and Andromeda, they arguably do more harm than good, costing you signal, and making color processing difficult.

 

What I use to combat light pollution is gradient reduction in processing.  That actually identifies light pollution by its spatial variation, it's greatest at the horizon, least over head.  Works on all targets, all sources of light pollution, equally well.

 

Suitable tools include ABE or DBE in PixInsight, WIPE in Startools, something in Astro Pixel Processor.  There's a decent Gradient xTerminator plugin for Photoshop.

 

Pretty much all serious imagers use gradient reduction.  Some add a light pollution filter, but mostly only with emission nebula.

 

Below is an Andromeda I did.  Red Zone, Bortle 7, mag per arc sec squared low 18s. Nikon D5500.  No (not so) magic light pollution filter was used, but I did work hard on gradient reduction.

 

37X120 = 1.2 hours, could have done better with more.  Better version and all details here.

 

https://www.astrobin.com/263253/J/

 

m31final_small.jpg


Edited by bobzeq25, 24 September 2020 - 10:59 PM.

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#3 neaptide

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Posted 24 September 2020 - 11:06 PM

I used the wipe module in StarTools, but it’s a fine line between getting rid of the gradients and keeping the data intact. Maybe I’ll combine the data with some additional  subs without using the LP filter. 



#4 zxx

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Posted 25 September 2020 - 10:54 AM

. Maybe I’ll combine the data with some additional  subs without using the LP filter. 

That's what I did, 30% with Orion sky glow filter ( 4 min subs ) the rest 2 min subs no filter all from my red zone with stock K50.

 

M31 done 77.jpg


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#5 neaptide

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Posted 25 September 2020 - 11:32 AM

Thanks zxx. I’ll add data next clear night. I also think I was a little heavy handed with the wipe module in StarTools. I’m working on a reprocess right now and it looks somewhat better. 


Edited by neaptide, 25 September 2020 - 11:33 AM.


#6 Skyshooter

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Posted 25 September 2020 - 11:33 AM

I think you did a great job. From a red zone, amazing.

I see so many of these shots over stretched but yours looks pretty natural.

I'd be happy with that too!

 

Cheers,

-Ed


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#7 zxx

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Posted 25 September 2020 - 11:58 AM

Thanks zxx. I’ll add data next clear night. I also think I was a little heavy handed with the wipe module in StarTools. I’m working on a reprocess right now and it looks somewhat better. 

I'm not much at processing either, I do most of it in DSS then polish up with LR.  But I definitely get a cleaner image on galaxies adding filtered data to the stack.



#8 neaptide

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Posted 25 September 2020 - 12:02 PM

I think you did a great job. From a red zone, amazing.

I see so many of these shots over stretched but yours looks pretty natural.

I'd be happy with that too!

 

Cheers,

-Ed

Thanks for the encouraging words Ed.

Astrophotography has a lot of challenges especially in the suburbs of NYC.



#9 N1ghtSc0p3

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Posted 25 September 2020 - 02:20 PM

Hi John,

 

I recently did M31, ASI294MC Pro, with an IDAS LPS P2, 43 x 90s subs from my Bortle 8 backyard. Gain was 0, and temp at -10C.

 

get.jpg?insecure

 

I'm still working on the processing (and building a new PC for that), so I'll probably post a revision at some point. But Bob's point is well taken...refining processing steps can do wonders to get the most out of the data one collects.

 

You didn't say if you did this all in one night, or collected the data over multiple nights?

 

If you can wait til later in the evening/morning, would you get better data as M31 moves away from the LED streetlights?

 

I find that I am only limited to ~1/3ish of the sky for imaging, as the rest of my 'window' is obscured by houses, trees, and/or gets washed out in the light dome that's to the East of me. This means that I don't image (most) objects until they're at or near the zenith, and thence to the West. The altitude of an object then determines if it will go behind a neighbor's house or be available down to the western horizon. All this to say that it is possible to plan the imaging schedule to maximize time on target that's away from light sources, which will go a long ways towards having better data to process...or rather the processing will have a more noticeable impact because you're getting better SNR.


Edited by N1ghtSc0p3, 25 September 2020 - 02:30 PM.

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#10 neaptide

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Posted 25 September 2020 - 05:03 PM

 

If you can wait til later in the evening/morning, would you get better data as M31 moves away from the LED streetlights?

 

 

This makes sense, thanks. On the first night I started imaging M31 right after it got dark and it was still very low in the sky. The second night it was clear early then the clouds rolled in so I have a lot of data from lower altitudes. I don't get a lot of clear nights, especially without the moon, so it's hard for me to be picky when I image. I definitely need to improve my processing skills. For some reason my colors always look different from the majority of posts I see here.  shrug.gif. I use Startools the tweak in GIMP, but about to give Astro Pixel Processer a try. Maybe that will help.

 

Your M31 is great!!


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#11 neaptide

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Posted 25 September 2020 - 05:04 PM

I'm not much at processing either, I do most of it in DSS then polish up with LR.  But I definitely get a cleaner image on galaxies adding filtered data to the stack. 

 

I like your M31 so whatever your doing is working.



#12 neaptide

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Posted 25 September 2020 - 05:07 PM

Here's another attempt. Less noise reduction and I think the color is a little better too.

 

M31 IDAS LPS D1 StarTools 2.jpg


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#13 N1ghtSc0p3

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Posted 27 September 2020 - 01:36 PM

This makes sense, thanks. On the first night I started imaging M31 right after it got dark and it was still very low in the sky. The second night it was clear early then the clouds rolled in so I have a lot of data from lower altitudes. I don't get a lot of clear nights, especially without the moon, so it's hard for me to be picky when I image. I definitely need to improve my processing skills. For some reason my colors always look different from the majority of posts I see here.  shrug.gif. I use Startools the tweak in GIMP, but about to give Astro Pixel Processer a try. Maybe that will help.

 

Your M31 is great!!

Thanks John. I have a feeling that there are a lot of us that can't be picky when we image. I've been out twice for 2-night stints since 01 August. There are apps and tools that will give you a forecast for astronomy (Astrospheric, Scope Nights, Meteoblue, etc.), so you can at least have an outline of a plan for what and when to image. Getting subs when objects are not near artificial light sources is one of the best things you can do to improve your data. Keep up the practice, you're def learning and getting better.



#14 neaptide

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Posted 01 October 2020 - 08:58 AM

Had another clear night last night so I figured I'd give M31 another shot without an LP filter. The moon was at 99% so my light pollution was definitely at it's peak. I also did a few things differently with the wipe module in StarTools. I think I got some good advice about LP filters and ill just deal with the gradients during post processing. 

 

This is not exactly an apples to apples comparison as this was also my first light with an ASI533mc Pro camera, otherwise the scope setup is the same. 

 

M31 ASI533 ST.jpg




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