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Newbie's M31, looking for suggestions for improvement

beginner astrophotography refractor dso
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#1 HoloTheWolf

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Posted 26 September 2020 - 07:15 PM

This is my first ever astrophotography work. Did a milky way project last month in Crater Lake, but DSO is something totally different so

I spent a bit of time combing through CN discussions regarding photographing M31. One useful information I got is that the total integration

time is key, which is critical for doing backyard AP in my Bortle 5/6 area.

 

Equipment-wise, mine is a pretty standard AP beginner set:

  • iOptron SkyGuider Pro + iPolar
  • WO Z61 Mark II + Flat61A + Optolong light pollution filter
  • Fujifilm X-T2

Some technical details:

  • Session 1: 9/22, 30" x 30
  • Session 2: 9/23, 30" x 201
  • Session 3: 9/24, 30" x 283
  • Session 4: 9/25, 30" x 270
  • Flat/DarkFlat/Dark/Bias: 50/50/30/50
  • Stacking: Astro Pixel Processor
  • Post-processing: Photoshop

Given my equipments, what should I do in order to get as many details of M31 as possible? Two most obvious places I can see:

  • Polar alignment. Stars near the edges of the frame are not rounded. 
  • Comparing to other M31 works, my background stars appear to be "bigger." My guess is focus is not spot on, even though I saw clear diffraction patterns.

Comments and suggestions are welcome. Thanks and clear nights!

Attached Thumbnails

  • M31.jpg

Edited by HoloTheWolf, 26 September 2020 - 08:36 PM.

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#2 zxx

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Posted 26 September 2020 - 07:27 PM

That's a nice first attempt, can your mount give longer exposures ?  I can go 4 min from my red zone with the Orion sky glow filter at ISO 800. Do you use the histo to know how long to expose ?


Edited by zxx, 26 September 2020 - 07:44 PM.

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#3 HoloTheWolf

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Posted 26 September 2020 - 08:39 PM

That's a nice first attempt, can your mount give longer exposures ?  I can go 4 min from my red zone with the Orion sky glow filter at ISO 800. Do you use the histo to know how long to expose ?

Thank you! I saw people doing much longer subs using the same mount, so I would definitely try to go beyond 30".

Could you elaborate a bit on how to use histogram to expose?



#4 zxx

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Posted 26 September 2020 - 09:23 PM

Thank you! I saw people doing much longer subs using the same mount, so I would definitely try to go beyond 30".

Could you elaborate a bit on how to use histogram to expose?

Put the data spike about 1/3 off the left   Check camera histo on light frame so it's about like this.

 

Capture histo.PNG


Edited by zxx, 26 September 2020 - 10:34 PM.

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#5 bobzeq25

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Posted 26 September 2020 - 11:54 PM

Excellent image.

 

Suggestion.  Lose the light pollution filter, unless it's a _very_ mild one that cuts out very little of the spectrum.  Like a Baader neodymium or an Orion Skyglow.  On a broadband target like Andromeda, you don't want to lose much signal.

 

Use the light pollution reduction tool (aka "gradient reduction") in APP.  That works well, because it's based on spatial variation of light pollution, not whacking out hunks of the spectrum.  It preserves target signal.


Edited by bobzeq25, 26 September 2020 - 11:55 PM.

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#6 limeyx

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Posted 27 September 2020 - 04:21 PM

Thank you! I saw people doing much longer subs using the same mount, so I would definitely try to go beyond 30".

Could you elaborate a bit on how to use histogram to expose?

With a good polar alignment, you should I think be able to get 60-90second subs.

 

I can push 120 seconds on my skyguider pro but my I have 300MM DSLR lens so I can probably push it a bit further

I even tried 240 seconds and got some usable frames and have since improved my gear, so definitely play with this


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#7 HoloTheWolf

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Posted 28 September 2020 - 01:45 AM

Excellent image.

 

Suggestion.  Lose the light pollution filter, unless it's a _very_ mild one that cuts out very little of the spectrum.  Like a Baader neodymium or an Orion Skyglow.  On a broadband target like Andromeda, you don't want to lose much signal.

 

Use the light pollution reduction tool (aka "gradient reduction") in APP.  That works well, because it's based on spatial variation of light pollution, not whacking out hunks of the spectrum.  It preserves target signal.

Thank you!

Removing the light pollution filter sounds a bit counter intuitive for suburban imagers, but this Pleiades picture says it is doable.

I'll definitely give it a try this week.



#8 HoloTheWolf

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Posted 28 September 2020 - 01:48 AM

With a good polar alignment, you should I think be able to get 60-90second subs.

 

I can push 120 seconds on my skyguider pro but my I have 300MM DSLR lens so I can probably push it a bit further

I even tried 240 seconds and got some usable frames and have since improved my gear, so definitely play with this

120 seconds, that is very impressive! I never thought a humble star tracker can do such a long sub. Looks like I still have much to learn.



#9 RJF-Astro

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Posted 28 September 2020 - 02:20 AM

Nice work! As I discovered recently, it is important to keep checking polar alignment on these trackers. I did not after moving to a target and that led to bad tracking in some cases.

 

Star reduction is often done in post processing. If you use Photoshop, there are a few techniques. First is part of Noel Carbonis action set. It is called 'Enhance DSO and reduce stars', a very cool action that I use a lot. The second technique I know if is use the 'Minimal' filter, a standard filter in Photoshop. Trevor Jones from Astrobackyard has a nice video on post processing, and he also talks about these techniques. 


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#10 F.Meiresonne

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Posted 28 September 2020 - 03:02 AM

Great image. Took me a year to get more or less thesame , and with help from CN


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#11 zxx

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Posted 28 September 2020 - 09:57 AM

Thank you!

Removing the light pollution filter sounds a bit counter intuitive for suburban imagers, but this Pleiades picture says it is doable.

I'll definitely give it a try this week.

I'm not familiar with APP for stacking, though with DSS you can set it to stack only the best frames. I actually look at each frame and pick the best before stacking, though 800 frames would take awhile lol.  I actually combine filtered and none filtered data for my M31 image from my red zone. 4 min subs with Orion sky glow filter, 2 min subs no filter.

 

Your stars in the corners look elongated, do you have the matching FF ?


Edited by zxx, 28 September 2020 - 10:22 AM.

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#12 HoloTheWolf

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Posted 28 September 2020 - 12:54 PM

I'm not familiar with APP for stacking, though with DSS you can set it to stack only the best frames. I actually look at each frame and pick the best before stacking, though 800 frames would take awhile lol.  I actually combine filtered and none filtered data for my M31 image from my red zone. 4 min subs with Orion sky glow filter, 2 min subs no filter.

 

Your stars in the corners look elongated, do you have the matching FF ?

Good idea. APP does not seem to have this option out of the box. But I read from a different thread that one can sort lights in APP

by "quality score" and then stack those with higher scores.

 

Integrating filtered and non-filtered frames, I guess this way light pollution and noise can be reduced and also details are also retained. Is that the idea? I'll also experiment with that.

Very interesting.

 

No sure why corner stars are elongated. PA might be one factor, but I do pair the scope with a field flattener. Or perhaps my FF is tilted.


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#13 zxx

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Posted 28 September 2020 - 01:18 PM

 

 

Integrating filtered and non-filtered frames, I guess this way light pollution and noise can be reduced and also details are also retained. Is that the idea? I'll also experiment with that.

Very interesting.

 

 

My best M31 image was my first attempt, I kept adding more data over two years for a total of 7 hours. I got the best result using filtered and unfiltered data. I'm not much at processing and only use DSS and LR though was happy with results using a guided CG-4 mount and ED80 and K50.   30 % 4 min Orion sky glow filter, 70 % 2 min no filter. 175 lights, 7 hours.

 

M31 done 77.jpg


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#14 HoloTheWolf

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Posted 29 September 2020 - 01:44 AM

Nice work! As I discovered recently, it is important to keep checking polar alignment on these trackers. I did not after moving to a target and that led to bad tracking in some cases.

 

Star reduction is often done in post processing. If you use Photoshop, there are a few techniques. First is part of Noel Carbonis action set. It is called 'Enhance DSO and reduce stars', a very cool action that I use a lot. The second technique I know if is use the 'Minimal' filter, a standard filter in Photoshop. Trevor Jones from Astrobackyard has a nice video on post processing, and he also talks about these techniques. 

That is a nice tip to make sure RA axis is aligned! Now I can recall that I tried to point the scope to M31 after PA. It is very likely that my PA went off during the process.

 

Thanks for the star reduction tips. That is exactly what I need.


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#15 Palmito

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Posted 29 September 2020 - 05:11 AM

Very nice! My first M31 was by far not as good, congrats!

 

 

Yes I would definitely add more integration time.

 

As suggested by others, I would also try to increase sub exposures.

But pay close attention to the stars, you'll get smaller stars with shorter exposures.

So you want to find the good balance to keep good small stars and good signal to noise ratio. Check my post here, where I compared different exposures:
https://www.cloudyni...sing/?p=9114715

 

Also I notice that depending on the time you shot, the moon might have been out, so you could try to shoot during new moon or when it has set.

 

 

If I may ask, I notice you're using a X-T2, how are you controlling it? With a remote control?

(A friend of mine has one and we failed to find a way to control it from a computer.)


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#16 HoloTheWolf

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Posted 29 September 2020 - 04:21 PM

Very nice! My first M31 was by far not as good, congrats!

 

Yes I would definitely add more integration time.

 

As suggested by others, I would also try to increase sub exposures.

But pay close attention to the stars, you'll get smaller stars with shorter exposures.

So you want to find the good balance to keep good small stars and good signal to noise ratio. Check my post here, where I compared different exposures:
https://www.cloudyni...sing/?p=9114715

 

Also I notice that depending on the time you shot, the moon might have been out, so you could try to shoot during new moon or when it has set.

 

If I may ask, I notice you're using a X-T2, how are you controlling it? With a remote control?

(A friend of mine has one and we failed to find a way to control it from a computer.)

Thanks for the tips, I'll definitely read through the discussions. Indeed as you noticed, the moon was out in all sessions and its impact is quite visible across all subs.

 

I agree, it would be nice if there is something like BackyardFuji. I just use a intervalometer to control the exposure time.


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#17 HoloTheWolf

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Posted 29 September 2020 - 04:26 PM

Your stars in the corners look elongated, do you have the matching FF ?

After going through my set up again, I realized I didn't set up the field flattener properly.

According to WO's website, I should set its back focus at the 12.9mm mark, but I never did.

What a bummer...LOL


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#18 bobzeq25

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Posted 29 September 2020 - 04:43 PM

Thank you!

Removing the light pollution filter sounds a bit counter intuitive for suburban imagers, but this Pleiades picture says it is doable.

I'll definitely give it a try this week.

Things are frequently counter intuitive in DSO AP, but this is not.

 

So called "light pollution" filters do not magically target light pollution, they simply rip out chunks of the spectrum.  The hope is that what they rip out is mostly light pollution, and what they pass is most of the target signal.  For emission nebulae and metal vapor lights, that can work.  By the time you get to broadband targets like clusters and nebulae, and LEDs, you're pretty much ripping out as much signal as you are noise.

 

Gradient reduction even works on moonlight, to a degree.  But the Moon still is a drawback to imaging.  I pretty much image nothing but star clusters when it's out.  No nebulae or galaxies.


Edited by bobzeq25, 29 September 2020 - 04:47 PM.

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#19 zxx

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Posted 29 September 2020 - 06:25 PM

After going through my set up again, I realized I didn't set up the field flattener properly.

According to WO's website, I should set its back focus at the 12.9mm mark, but I never did.

What a bummer...LOL

LOL, don't feel bad, I took 62x180s of M31 last week at a dark sky with the focus mask on the scope bangbang.gif

 

If you don't have one get one they help a lot, If you remove it after focusing lol.


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