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

M81/M82

  • Please log in to reply
45 replies to this topic

#1 limeyx

limeyx

    Viking 1

  • -----
  • topic starter
  • Posts: 857
  • Joined: 23 May 2020
  • Loc: Seattle, WA

Posted 23 January 2021 - 10:17 PM

First time using the AT60ED. For once I did not get the dreaded "Red/Green rings of death" from the D5300 but there is a weird mottled red patchy background (not sure if Noise reduction caused some of this)

Had a really hard time getting focus with the new focus mask and ended up eyeballing it, so it's definitely not perfect

Also around 3/4 of the way in, a black splotch appeared in the subs that was NOT in the first ones, OR the flats. I didn't touch anything and it was in the same sequence so not sure about that...

 

Had some great PHD guiding but I am still not happy with the stars. Also the first time with the field flattener -- It looks like maybe some star elongation but it's somewhat hard to tell so far.

 

I also feel like I blew out both main galaxies, yet I see a lot of recommendations to go to 10+ min subs (maybe with filters ?)

Any advice on pulling the details out, appreciated (non-modded camera and no filters)

 

This was the FIRST clear night in 2021 so even though the moon was out, I grabbed the chance and am reasonably OK with the result.

My focal length is obviously a bit limiting for galaxies but it's definitely an interesting challenge

 

Imaging telescopes or lenses: AstroTech AT60 ED AT60ED

Imaging cameras: Nikon d5300 (Non-Modded)

Mounts: iOptron Skyguider Pro

Guiding telescopes or lenses: William Optics UniGuide 32mm

Guiding cameras: ZWO ASI 120mm mini

Software: PixInsight / APT

 

Dates:Jan. 22, 2021

Frames: 105x180"

Integration: 5.2 hours

Avg. Moon age: 8.81 days

Avg. Moon phase: 64.96%

 

Full image: https://www.astrobin.com/0zodlb/

Attached Thumbnails

  • Final1.jpg

Edited by limeyx, 23 January 2021 - 10:18 PM.

  • Fernando134, chrysalis, bobzeq25 and 10 others like this

#2 celeron787

celeron787

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 07 Feb 2020
  • Loc: Singapore

Posted 23 January 2021 - 10:53 PM

Nice job! Would you mind sharing the stacked file, would love to try processing this.

Edited by celeron787, 23 January 2021 - 10:53 PM.


#3 readkonrad

readkonrad

    Sputnik

  • -----
  • Posts: 36
  • Joined: 24 May 2018

Posted 23 January 2021 - 11:00 PM

I wonder if that red mottling is actually you capturing a faint signal from the IFN. I remembered an amazing picture from user h2ologg that blew me away. The sky isn’t a flat black near M81/M82, at least not to a RASA8 in dark skies.
http://www.cloudynig...ld-with-m81-m82

I was angry with one of my first M42s because it had this faint red crescent around it. Took me a while to realize I was trying to process out Barnard’s Loop...


Edited by readkonrad, 23 January 2021 - 11:04 PM.


#4 limeyx

limeyx

    Viking 1

  • -----
  • topic starter
  • Posts: 857
  • Joined: 23 May 2020
  • Loc: Seattle, WA

Posted 23 January 2021 - 11:06 PM

I wonder if that red mottling is actually you capturing a faint signal from the IFN. I remembered an amazing picture from user h2ologg that blew me away. The sky isn’t a flat black near M81/M82, at least not to a RASA8 in dark skies.
http://www.cloudynig...ld-with-m81-m82

I was angry with one of my first M42s because it had this faint red crescent around it. Took me a while to realize I was trying to process out Barnard’s Loop...

Interesting. That is possible. I will do more research ... I had to crush a bit more than I wanted to get rid of it but maybe I should highlight it more - I am still really novice at processing (along with everything else)



#5 jonnybravo0311

jonnybravo0311

    Apollo

  • *****
  • Posts: 1,084
  • Joined: 05 Nov 2020
  • Loc: NJ, US

Posted 23 January 2021 - 11:06 PM

What ISO did you shoot? What does the histogram on your camera look like per sub?

 

Your stars look pretty good edge to edge and at the corners. Maybe just a touch elongated / egg-shaped, but I only noticed it when I pixel peeped at full resolution.

 

You've got some nice detail in the arms of Bode's. Focus might be a touch soft, which might be killing the details in the Cigar and bloating the stars a bit.

 

You can try to mitigate that red mottling by creating a luminance mask to protect your stars/galaxies, then desaturating the background and/or bringing down the red channel using curves.

 

Edit: to address the comments about that being IFN, I'm about 99% sure it isn't. That looks like standard OSC noise. The IFN around M81 is EXTREMELY faint and would require very dark skies and a bucketload of integration time to bring out.


Edited by jonnybravo0311, 23 January 2021 - 11:09 PM.


#6 limeyx

limeyx

    Viking 1

  • -----
  • topic starter
  • Posts: 857
  • Joined: 23 May 2020
  • Loc: Seattle, WA

Posted 23 January 2021 - 11:12 PM

Nice job! Would you mind sharing the stacked file, would love to try processing this.

Absolutely. I am a total novice at processing and especially galaxies, since it's been Nebula season

I think I need to adjust my dither down a bit - I left it at the same setting as the 300mm lens and it may be a bit strong

 

I would love to see what you, or anyone else can do with this ...

 

https://drive.google...iew?usp=sharing



#7 brlasy1

brlasy1

    Vostok 1

  • *****
  • Posts: 121
  • Joined: 13 Jan 2020
  • Loc: Texas

Posted 23 January 2021 - 11:16 PM

First time using the AT60ED. For once I did not get the dreaded "Red/Green rings of death" from the D5300 but there is a weird mottled red patchy background (not sure if Noise reduction caused some of this)

Had a really hard time getting focus with the new focus mask and ended up eyeballing it, so it's definitely not perfect

Also around 3/4 of the way in, a black splotch appeared in the subs that was NOT in the first ones, OR the flats. I didn't touch anything and it was in the same sequence so not sure about that...

 

Had some great PHD guiding but I am still not happy with the stars. Also the first time with the field flattener -- It looks like maybe some star elongation but it's somewhat hard to tell so far.

 

I also feel like I blew out both main galaxies, yet I see a lot of recommendations to go to 10+ min subs (maybe with filters ?)

Any advice on pulling the details out, appreciated (non-modded camera and no filters)

 

This was the FIRST clear night in 2021 so even though the moon was out, I grabbed the chance and am reasonably OK with the result.

My focal length is obviously a bit limiting for galaxies but it's definitely an interesting challenge

 

Imaging telescopes or lenses: AstroTech AT60 ED AT60ED

Imaging cameras: Nikon d5300 (Non-Modded)

Mounts: iOptron Skyguider Pro

Guiding telescopes or lenses: William Optics UniGuide 32mm

Guiding cameras: ZWO ASI 120mm mini

Software: PixInsight / APT

 

Dates:Jan. 22, 2021

Frames: 105x180"

Integration: 5.2 hours

Avg. Moon age: 8.81 days

Avg. Moon phase: 64.96%

 

Full image: https://www.astrobin.com/0zodlb/

Better than my first attempt.  I need a field flattener.

 

M81 and M82

  • limeyx likes this

#8 limeyx

limeyx

    Viking 1

  • -----
  • topic starter
  • Posts: 857
  • Joined: 23 May 2020
  • Loc: Seattle, WA

Posted 23 January 2021 - 11:18 PM

What ISO did you shoot? What does the histogram on your camera look like per sub?

 

Your stars look pretty good edge to edge and at the corners. Maybe just a touch elongated / egg-shaped, but I only noticed it when I pixel peeped at full resolution.

 

You've got some nice detail in the arms of Bode's. Focus might be a touch soft, which might be killing the details in the Cigar and bloating the stars a bit.

 

You can try to mitigate that red mottling by creating a luminance mask to protect your stars/galaxies, then desaturating the background and/or bringing down the red channel using curves.

 

Edit: to address the comments about that being IFN, I'm about 99% sure it isn't. That looks like standard OSC noise. The IFN around M81 is EXTREMELY faint and would require very dark skies and a bucketload of integration time to bring out.

Thanks! This is ISO400/180s, which is about the max I think I can push this mount. Although I had to do a LOT more messing around framing than usual

I shot 400 not 200 to try to avoid the Nikon "rings of death"

 

The multi-star guiding in PHD2, coupled with changing the loop from 4 to 1 seconds, got my guiding at 0.84RMS for 5.5 hours, compared to the usual 1.75-2 so I was really happy there

 

Yeah focus is not 100%. The stars were super faint. I initially focused on a much brighter star but I just could not get the mask to work. The first sub was horrid and so I had to eyeball it on the target and this was the best I could do

 

I also think its noise. I did crush it a bit but if I go too far, then I start to lose the galaxy

Obviously galaxy season is not going to be my friend here with this focal length

 

As you can see, I didn't really need a cooled camera smile.gif

 

EDIT: Yeah I did bring down the BG with a mask but I backed it out a bit because I started to lose the galaxy details

Attached Thumbnails

  • IMG-4692-small.jpg

Edited by limeyx, 23 January 2021 - 11:22 PM.

  • jonnybravo0311 likes this

#9 limeyx

limeyx

    Viking 1

  • -----
  • topic starter
  • Posts: 857
  • Joined: 23 May 2020
  • Loc: Seattle, WA

Posted 23 January 2021 - 11:21 PM

Better than my first attempt.  I need a field flattener.

 

Yeah I really didn't want to spend 1/2 the price of the scope on the flattener. Thankfully I had a birthday and christmas present coming! I got the William Optics one because it has a built-in rotator which is super helpful


  • brlasy1 likes this

#10 jonnybravo0311

jonnybravo0311

    Apollo

  • *****
  • Posts: 1,084
  • Joined: 05 Nov 2020
  • Loc: NJ, US

Posted 23 January 2021 - 11:22 PM

LOL... hope you had a couple dew heaters on your scopes.



#11 limeyx

limeyx

    Viking 1

  • -----
  • topic starter
  • Posts: 857
  • Joined: 23 May 2020
  • Loc: Seattle, WA

Posted 23 January 2021 - 11:23 PM

LOL... hope you had a couple dew heaters on your scopes.

Just the main scope. The guider doesn't seem to need it, which is good because it's really small and hard to find a heater



#12 readkonrad

readkonrad

    Sputnik

  • -----
  • Posts: 36
  • Joined: 24 May 2018

Posted 23 January 2021 - 11:30 PM

If it’s not IFN then I’ve got good news: this is something that can be fixed by throwing time and $$$ at it!
Enjoy your new scope, stay warm!
  • limeyx likes this

#13 limeyx

limeyx

    Viking 1

  • -----
  • topic starter
  • Posts: 857
  • Joined: 23 May 2020
  • Loc: Seattle, WA

Posted 23 January 2021 - 11:31 PM

If it’s not IFN then I’ve got good news: this is something that can be fixed by throwing time and $$$ at it!
Enjoy your new scope, stay warm!

Thanks. I may try more subs at a shorter duration next time. Right now there is no end in sight to clouds, but this target will be around for a bit and I'd like to focus on it a bit more (pun intended!)


  • jonnybravo0311 likes this

#14 readkonrad

readkonrad

    Sputnik

  • -----
  • Posts: 36
  • Joined: 24 May 2018

Posted 23 January 2021 - 11:39 PM

I hear you, an autofocus system is high on my wish list, it’d be nice to automate that task and not always be worried that I haven’t gotten it quite right.
  • limeyx likes this

#15 Mike in Rancho

Mike in Rancho

    Ranger 4

  • -----
  • Posts: 318
  • Joined: 15 Oct 2020
  • Loc: Alta Loma, CA

Posted 24 January 2021 - 04:19 AM

Alas, ISO 400, which is my go-to, hasn't rid me of rainbow rings at all times.  But I'm still trying to think of things, meanwhile getting better at processing it.

 

Nice image though, congrats on first light.  Is that three of our recent newbie class now that all picked M81 for first light when the new scope arrived?  Funny.

 

I haven't tried one of those masks (probably never will), but have otherwise given up on focus assists like the FWHM in BYN.  Maybe I could perfect it if I had the laptop closer to the telescope.  But even so, I usually find out that my viewfinder focus was dead on and all I did was mess it up lol.  The key is a big zoom, and then when adjusting the fine focus knob I can usually find one point where a super faint star (other than my main focusing star) in the FOV is just barely showing up.  And that's where I lock it.

 

That double dust bunny (or maybe small iceberg on your objective lens?) was a bit of trouble to deal with.  As was the mottling.  In fact, you had some really strong color casts that I was not expecting.  Only time I've seen something like that is when I blew my flats out way way too far to the right.  Here it is in the ST wipe (which provides a strong stretch so you can find faults).

 

LMYX M81 stretch.jpg

 

I dealt with it using maximum gradient removal, which I usually don't like to do, and then a reasonably moderate final stretch.  There were still some areas I had to select and kill off manually.  When it came to color balance, wow it was really really green!  But I think I managed to tame it down fair enough and then get some good color in the stars too.

 

Funny I had just reprocessed my original M81 earlier today too.  A good bit better than I was at doing this 2 months ago.

 

Four galaxies you got here?  Nice!

 

LMYX M81 ST1A 1200px.jpg


  • jonnybravo0311 likes this

#16 Huangdi

Huangdi

    Apollo

  • *****
  • Posts: 1,005
  • Joined: 24 Jul 2019

Posted 24 January 2021 - 08:30 AM

I wonder if that red mottling is actually you capturing a faint signal from the IFN. I remembered an amazing picture from user h2ologg that blew me away. The sky isn’t a flat black near M81/M82, at least not to a RASA8 in dark skies.
http://www.cloudynig...ld-with-m81-m82
I was angry with one of my first M42s because it had this faint red crescent around it. Took me a while to realize I was trying to process out Barnard’s Loop...


Unlikely. The IFN starts showing up when Holmberg IX is well defined. It is present in this image, but not strong. I've recently taken two images of that region, where the IFN showed up nicely, and it always started appearing after the small blue Blob was shown clearly.

Nice image, by the way! 🙏
  • limeyx likes this

#17 limeyx

limeyx

    Viking 1

  • -----
  • topic starter
  • Posts: 857
  • Joined: 23 May 2020
  • Loc: Seattle, WA

Posted 24 January 2021 - 12:07 PM

Alas, ISO 400, which is my go-to, hasn't rid me of rainbow rings at all times.  But I'm still trying to think of things, meanwhile getting better at processing it.

 

Nice image though, congrats on first light.  Is that three of our recent newbie class now that all picked M81 for first light when the new scope arrived?  Funny.

 

I haven't tried one of those masks (probably never will), but have otherwise given up on focus assists like the FWHM in BYN.  Maybe I could perfect it if I had the laptop closer to the telescope.  But even so, I usually find out that my viewfinder focus was dead on and all I did was mess it up lol.  The key is a big zoom, and then when adjusting the fine focus knob I can usually find one point where a super faint star (other than my main focusing star) in the FOV is just barely showing up.  And that's where I lock it.

 

That double dust bunny (or maybe small iceberg on your objective lens?) was a bit of trouble to deal with.  As was the mottling.  In fact, you had some really strong color casts that I was not expecting.  Only time I've seen something like that is when I blew my flats out way way too far to the right.  Here it is in the ST wipe (which provides a strong stretch so you can find faults).

 

attachicon.gifLMYX M81 stretch.jpg

 

I dealt with it using maximum gradient removal, which I usually don't like to do, and then a reasonably moderate final stretch.  There were still some areas I had to select and kill off manually.  When it came to color balance, wow it was really really green!  But I think I managed to tame it down fair enough and then get some good color in the stars too.

 

Funny I had just reprocessed my original M81 earlier today too.  A good bit better than I was at doing this 2 months ago.

 

Four galaxies you got here?  Nice!

 

attachicon.gifLMYX M81 ST1A 1200px.jpg

Thank you for the analysis ! That black spot is a complete mystery. It was NOT present in the first 75% of lights and then suddenly appeared for no reason. It is not in the flats. I inspected the lens at the end of the night and I could not see anything

It's in the same place in each frame...

 

The mottling - I have no idea. My flats are if anything I think a little under, although their histogram is a little weird as it has three peaks. PI statistics says they are around 7100 ADU out of 16384. I did take some longer flats. I dim the light panel with paper to extend the exposure time. Maybe that's causing me more issues than normal?

 

Those green color casts are in every image I take -- literally the whole thing looks green before I do background extraction. I assumed that was normal for Bortle6 but maybe something else is going on ? It's a used camera so maybe something is not quite right. Its set to everything manual etc and is not modded

 

The moon was quite bright behind me (except for the last 45 mins or so) which I think accounts for the left gradient

 

I usually dont focus with the camera display as I am desperately trying to avoid moving the mount. I did live view but it didn't seem effective, so I did my best with test shots

 

I haven't moved the focus etc so maybe I can try a different way to get flats. There is a lot of white paper in order to tame down the exposure on them. I guess the mottling is different/better than the rings but not sure as it's also hard to deal with

 

EDIT: Assuming that's my data you posted, you did better than me on the color, especially in the cigar galaxy -- I need to go back and re-do this. I may restack it a few different ways and see if I can improve the stack


Edited by limeyx, 24 January 2021 - 12:10 PM.

  • Mike in Rancho likes this

#18 limeyx

limeyx

    Viking 1

  • -----
  • topic starter
  • Posts: 857
  • Joined: 23 May 2020
  • Loc: Seattle, WA

Posted 24 January 2021 - 12:08 PM

Unlikely. The IFN starts showing up when Holmberg IX is well defined. It is present in this image, but not strong. I've recently taken two images of that region, where the IFN showed up nicely, and it always started appearing after the small blue Blob was shown clearly.

Nice image, by the way!

Thanks. I am definitely a rank amateur here, and a lot of work needed.



#19 limeyx

limeyx

    Viking 1

  • -----
  • topic starter
  • Posts: 857
  • Joined: 23 May 2020
  • Loc: Seattle, WA

Posted 24 January 2021 - 02:19 PM

Something that also just occurred to me is that this was the first time I ran a USB hub on the mount to reduce the number of cables.

 

I have a small USB dew heater that was plugged into the same hub (for power) as the camera. I've heard this can cause issues.

I wish I had time for an A/B comparison but maybe next time I will run this to the power strip I use (ideally to an alternate 110V source entirely, which I do have but its on the ground and I am not sure the cable will reach)



#20 Mike in Rancho

Mike in Rancho

    Ranger 4

  • -----
  • Posts: 318
  • Joined: 15 Oct 2020
  • Loc: Alta Loma, CA

Posted 24 January 2021 - 08:11 PM

Thank you for the analysis ! That black spot is a complete mystery. It was NOT present in the first 75% of lights and then suddenly appeared for no reason. It is not in the flats. I inspected the lens at the end of the night and I could not see anything

It's in the same place in each frame...

 

The mottling - I have no idea. My flats are if anything I think a little under, although their histogram is a little weird as it has three peaks. PI statistics says they are around 7100 ADU out of 16384. I did take some longer flats. I dim the light panel with paper to extend the exposure time. Maybe that's causing me more issues than normal?

 

Those green color casts are in every image I take -- literally the whole thing looks green before I do background extraction. I assumed that was normal for Bortle6 but maybe something else is going on ? It's a used camera so maybe something is not quite right. Its set to everything manual etc and is not modded

 

The moon was quite bright behind me (except for the last 45 mins or so) which I think accounts for the left gradient

 

I usually dont focus with the camera display as I am desperately trying to avoid moving the mount. I did live view but it didn't seem effective, so I did my best with test shots

 

I haven't moved the focus etc so maybe I can try a different way to get flats. There is a lot of white paper in order to tame down the exposure on them. I guess the mottling is different/better than the rings but not sure as it's also hard to deal with

 

EDIT: Assuming that's my data you posted, you did better than me on the color, especially in the cigar galaxy -- I need to go back and re-do this. I may restack it a few different ways and see if I can improve the stack

On further reflection, my own M81 required capping greens too.  Maybe it's a thing in that direction lol.

 

It's for sure your data, and there is color in there.  It took some coaxing, as at first it popped up rather grayscale in the color module for me also.  But it's there.

 

Same for me on the flats, although I slide the paper over a bit every 5 shots, to keep from possibly picking up patterns of paper grain.


  • limeyx likes this

#21 OrionRockstar

OrionRockstar

    Lift Off

  • -----
  • Posts: 1
  • Joined: 13 Oct 2020

Posted 25 January 2021 - 01:45 AM

Several things,

1) Make sure the space between the flattener and sensor is correct. It doesn't appear to be an issue here but it is better to be safe than sorry. 

2) Make sure you have good calibration frames. Darks, flats, and bias. Your mottling issues is more than likely coming from bias or darks frames. Judging by the frost on the gear, I doubt you got your dark temps to match the lights.

3) I would suggest shooting at a higher iso since you are shooting 3 min subs. Higher iso cuts the well depth

4) Shoot at a much higher iso when focusing. The goal here is to just expose long enough to where the stars are visible enough to tell you need to change focus. Don't be afraid to spend some time fine tuning.

5) The green cast is the due to the bayer matrix. RGGB, DSLRs have green bias.

 

You got a nice image despite it flaws. Here is a quick process I did in startools.

 

 

Attached Thumbnails

  • M81-M82-Stackedv2.png


#22 limeyx

limeyx

    Viking 1

  • -----
  • topic starter
  • Posts: 857
  • Joined: 23 May 2020
  • Loc: Seattle, WA

Posted 25 January 2021 - 11:43 AM

Several things,

1) Make sure the space between the flattener and sensor is correct. It doesn't appear to be an issue here but it is better to be safe than sorry. 

2) Make sure you have good calibration frames. Darks, flats, and bias. Your mottling issues is more than likely coming from bias or darks frames. Judging by the frost on the gear, I doubt you got your dark temps to match the lights.

3) I would suggest shooting at a higher iso since you are shooting 3 min subs. Higher iso cuts the well depth

4) Shoot at a much higher iso when focusing. The goal here is to just expose long enough to where the stars are visible enough to tell you need to change focus. Don't be afraid to spend some time fine tuning.

5) The green cast is the due to the bayer matrix. RGGB, DSLRs have green bias.

 

You got a nice image despite it flaws. Here is a quick process I did in startools.

Thank you!

 

1/ I have it at 12.9mm (or as close as I can get) which I believe is recommended w/out a filter in. Stars look OK - there is some elongation sometimes but I *think* this is just because I have the SkyGuider and not a true mount

2/ The data is in my lights (will post later). I stacked just lights and I still see it. In this case, I had bias, darks (only 5), flats and flat-darks. I have stacked this data 87 ways and I can see the flats working to get rid of dust / other stuff but not the red

3/ I went for 400. 200 was recommended but yeah maybe 800. I already feel like I overexposed the galaxy cores (but it could be focus)

I am stumped on exposure here because many people are doing 5-10 min subs (although maybe with filters)

I feel like I am already blowing things out here but maybe it was the moon and poor focus ?

4/ Yeah but then everything looks blurry and its really hard to see the spikes - more practice

5/ Understood but man .... its *realllllly* green in PI (will post an example)



#23 jonnybravo0311

jonnybravo0311

    Apollo

  • *****
  • Posts: 1,084
  • Joined: 05 Nov 2020
  • Loc: NJ, US

Posted 25 January 2021 - 12:26 PM

It's supposed to be *realllllly* green. Here's a side-by-side comparison of my M81 data fresh from the stacker with only a dynamic crop applied. The difference? The one on the left is a linked stretch. The one on the right is an unlinked stretch.

 

linked Vs unlinked


#24 DubbelDerp

DubbelDerp

    Apollo

  • *****
  • Posts: 1,383
  • Joined: 14 Sep 2018
  • Loc: Upper Peninsula of Michigan

Posted 25 January 2021 - 12:29 PM

I would suspect that the red mottling is just due to light pollution, and will improve with more integration time or less moonlight. If I shoot under bright moonlight and stretch the background too much, I get a very similar background to what you're seeing. So I don't think there's anything wrong with what you are doing other than to get more integration time.

 

I wouldn't worry too much about the exposure time. At f/6 you might be able to get away with a 10 minute sub, but it'll take a dark site and little moonlight. It may be necessary if you're going after IFN, but you'll almost certainly blow out the galaxies in that case.

 

I have a tough time with short exposures with using a bahtinov mask, just because the camera jiggles around too much to get a sharp image of the spikes. It helps in my case to set the exposure to like 10 seconds or so and trigger it through the computer or with an intervalometer to keep everything as steady as possible, and the longer exposure reduces the impact of the camera shutter shaking the setup.

 

Edit - here's my attempt with APP and GIMP... I over-saturated it, I think.

Annotation 2021-01-25 130636.jpg


Edited by DubbelDerp, 25 January 2021 - 01:08 PM.


#25 pedxing

pedxing

    Vanguard

  • *****
  • Posts: 2,385
  • Joined: 03 Nov 2009
  • Loc: SE Alaska

Posted 25 January 2021 - 01:46 PM

Addressing your "green" comment:

 

First steps in PI after integration are the color correction steps:

 

1. Use Channel Extraction to separate the image into separate R, G and B channels.

2. Apply Linear Fit on the B and G channels with the R channel as the reference.

3. Use Channel Combination to re-combine the channels once you have done the linear fit.

4. Background Neutralization on the re-combined image using a preview area of a representative area of background that doesn't contain nebulosity, obvious gradient or stars as the reference.

5. Color Calibration using a preview (that either contains a group of non-blown out stars with structure detection turned on or a preview that contains just a galaxy with structure detection turned off) as a white reference and the same preview that you used in the previous step as the background reference.

 

This should get your color very close. If you still see a green cast, you can use SCNR at about 60% to remove any residual green.


Edited by pedxing, 25 January 2021 - 01:49 PM.

  • limeyx likes this


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