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Andromeda Galaxy (M31), M32 (NGC 221), M110 ((NGC 205)

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Greg Erianne
(@greg-erianne)
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Posts: 94
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First time photographing the Andromeda Galaxy with a dedicated astro camera.  I wasn't sure how to avoid blowing out the central bulge so I opted for 3 min exposures, but I think I would have been better off with 2 minute subs.  The core looks a bit blown out to me. 

This wasn't as easy to process as I thought it would be!  What do other folks use as far as gain/sub-exposure length so the core is more visible? 

AT60ED and field flattener
iOptron SkyGuider Pro with guiding via ASIAir Plus and an ASI120mm mini/30F4 guide scope
ASI2600 MC Pro (no filters used)
3 min x 50 lights (2.5 hrs) with corresponding dark, flat, dark-flat, and bias calibration frames
Stacked/Processed in Astro Pixel Processor and in Adobe Photoshop 2022


   
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Paul Walker
(@pwalker)
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Hi Greg.  Nicely done rendition.  What you did is the easiest way to compromise between not too blown out core and enough data in the outskirts.  I am one of these imagers who when processing galaxy images likes to leave the sky background on the lighter side so as preserve some of the faintest details in the galaxy's extremities.  Pretty much all galaxies are hard to process.  Modern CMOS sensors do quite well with the shorter exposures as long as you have enough data (total time) which you have. Another option is to take 2 sets of data, short exposures for the core and long exposures for the rest and create a high dynamic range (HDR) image.  A third way, which I have used on M42 (The Orion Neb) is to do intermediate exposures like you did and process them 2 ways (similar HDR and maybe the same technique that is sometimes used).  I processed the stack once to bring out detail in the core and again for the outer details.  I then carefully and selectively cloned the center of the first processing into the center of the 2nd processing using a wide feathering on the cloning tool.  I have not tried this for the Andromeda Galaxy, it should work but may be harder with M42.

A note on calibration frames.  In my opinion you only need darks and flats if you goal is aesthetically pleasing images.  The dark-flat, and bias frames are less important unless you are creating images for scientific purposes.  Or maybe pushing the limits, but I think it would be better to take more data instead.  I have never used dark-flat, and bias frames.

 


   
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Greg Erianne
(@greg-erianne)
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Posted by: @pwalker

Hi Greg.  Nicely done rendition.  What you did is the easiest way to compromise between not too blown out core and enough data in the outskirts.  I am one of these imagers who when processing galaxy images likes to leave the sky background on the lighter side so as preserve some of the faintest details in the galaxy's extremities.  Pretty much all galaxies are hard to process.  Modern CMOS sensors do quite well with the shorter exposures as long as you have enough data (total time) which you have. Another option is to take 2 sets of data, short exposures for the core and long exposures for the rest and create a high dynamic range (HDR) image.  A third way, which I have used on M42 (The Orion Neb) is to do intermediate exposures like you did and process them 2 ways (similar HDR and maybe the same technique that is sometimes used).  I processed the stack once to bring out detail in the core and again for the outer details.  I then carefully and selectively cloned the center of the first processing into the center of the 2nd processing using a wide feathering on the cloning tool.  I have not tried this for the Andromeda Galaxy, it should work but may be harder with M42.

A note on calibration frames.  In my opinion you only need darks and flats if you goal is aesthetically pleasing images.  The dark-flat, and bias frames are less important unless you are creating images for scientific purposes.  Or maybe pushing the limits, but I think it would be better to take more data instead.  I have never used dark-flat, and bias frames.

 

Thanks, Paul.  That all makes perfect sense.  I suppose had I masked the core (which I didn't) when processing I could have prevented it from being exposed.  I'll give that a try and then combine it with the rest of the image.

Using the dedicated astro camera, the calibration frames don't take away from my imaging time, which is very nice.  I do all my calibration frames the following day by cooling the camera to whatever it was when I imaged, keeping everything else the same, e.g., focus, filter, etc., and then doing all the calibration frames.  I absolutely love that part of using a dedicated, cooled astro camera.  Makes things so much easier.  This was the first time I used dark-flats but I think they work better than bias frames for these cameras and they're very quick.  I know a lot of it is overkill, but I really like how clean the images are after stacking with calibration frames.  (Probably PTSD from using my noisy canon DSLR!!)

Thanks again for the advice, Paul!

Greg

This post was modified 3 months ago by Greg Erianne

   
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Paul Walker
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I'm still using a DSLR so of course I have to do my dark the same night.  You might as well take the "extra" calibration frames when it's that easy.  This will be for those just getting into imaging (I assume you are aware of this)- You have to be careful how you use the dark-flat, and bias frames all the frames have the bias data and if applied incorrectly one will add "noise" but subtracting out the bias data more than once.  That said many of the stacking programs, including Deep Sky Stacker, automatically handle this properly.  So it's only the programs where one has to tell the software how to apply each file type that this could be an issue.

I upgraded from a 2008 DLSR camera to a 2017 camera a couple years ago with a notable improvement in the results.  I also went from 8 Mp to 24 Mp, which even if the inherent pixel to pixel noise was the same, reduced the spatial size of the noise.


   
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Greg Erianne
(@greg-erianne)
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Joined: 1 year ago
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Posted by: @pwalker

Hi Greg.  Nicely done rendition.  What you did is the easiest way to compromise between not too blown out core and enough data in the outskirts.  I am one of these imagers who when processing galaxy images likes to leave the sky background on the lighter side so as preserve some of the faintest details in the galaxy's extremities.  Pretty much all galaxies are hard to process.  Modern CMOS sensors do quite well with the shorter exposures as long as you have enough data (total time) which you have. Another option is to take 2 sets of data, short exposures for the core and long exposures for the rest and create a high dynamic range (HDR) image.  A third way, which I have used on M42 (The Orion Neb) is to do intermediate exposures like you did and process them 2 ways (similar HDR and maybe the same technique that is sometimes used).  I processed the stack once to bring out detail in the core and again for the outer details.  I then carefully and selectively cloned the center of the first processing into the center of the 2nd processing using a wide feathering on the cloning tool.  I have not tried this for the Andromeda Galaxy, it should work but may be harder with M42.

A note on calibration frames.  In my opinion you only need darks and flats if you goal is aesthetically pleasing images.  The dark-flat, and bias frames are less important unless you are creating images for scientific purposes.  Or maybe pushing the limits, but I think it would be better to take more data instead.  I have never used dark-flat, and bias frames.

 

I tried processing my M31 photo again (third way you mentioned) and it seems maybe a little better in terms of the core, but maybe not as 'punchy'.  The next time I'm imaging Andromeda, I'll have to try the 2 sets of data method.  I'm sure it will be easier to process!

Greg


   
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Terri Zittritsch
(@terri)
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Joined: 3 years ago
Posts: 165
 
Posted by: @greg-erianne

First time photographing the Andromeda Galaxy with a dedicated astro camera.  I wasn't sure how to avoid blowing out the central bulge so I opted for 3 min exposures, but I think I would have been better off with 2 minute subs.  The core looks a bit blown out to me. 

This wasn't as easy to process as I thought it would be!  What do other folks use as far as gain/sub-exposure length so the core is more visible? 

AT60ED and field flattener
iOptron SkyGuider Pro with guiding via ASIAir Plus and an ASI120mm mini/30F4 guide scope
ASI2600 MC Pro (no filters used)
3 min x 50 lights (2.5 hrs) with corresponding dark, flat, dark-flat, and bias calibration frames
Stacked/Processed in Astro Pixel Processor and in Adobe Photoshop 2022

Hi Greg, nice capture.     Colors are hard to tease out of galaxy photos (a lot are really difficult).     On this, one thing I'm seeing is a heavy hand in noise reduction.   Is this true?      The center of the galaxy is not blown out that much.  You could have exposed a bit less to keep the blown out center less exposed.   3 Min looks like enough to blow out the stars as well.    On Dark-Flat and Bias, you shouldn't need both.     The thinking for some time now has been that dark-flats (to calibrate darks) is all you should need for a CMOS camera along with your darks and flats, and you should only need it for each exposure time/gain/temperature and then create a library over time and just re-use them.     Darks is the same way, create a library and then re-use.   I never take darks and or dark flats in my imaging time.     But Flats as you know need to be taken before you rotate the camera on the scope.     You may get some more detail in there due to lower exposure, but the thing that jumps out at me is the softness of the galaxy, especially along the front edge.

 

Terri

 

 

 


   
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Greg Erianne
(@greg-erianne)
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Joined: 1 year ago
Posts: 94
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Posted by: @terri
Hi Greg, nice capture.     Colors are hard to tease out of galaxy photos (a lot are really difficult).     On this, one thing I'm seeing is a heavy hand in noise reduction.   Is this true?      The center of the galaxy is not blown out that much.  You could have exposed a bit less to keep the blown out center less exposed.   3 Min looks like enough to blow out the stars as well.    On Dark-Flat and Bias, you shouldn't need both.     The thinking for some time now has been that dark-flats (to calibrate darks) is all you should need for a CMOS camera along with your darks and flats, and you should only need it for each exposure time/gain/temperature and then create a library over time and just re-use them.     Darks is the same way, create a library and then re-use.   I never take darks and or dark flats in my imaging time.     But Flats as you know need to be taken before you rotate the camera on the scope.     You may get some more detail in there due to lower exposure, but the thing that jumps out at me is the softness of the galaxy, especially along the front edge.

Thanks for taking a look, Terri!  Yes, guilty of the heavy hand.  As I said (confessed) in reply to Paul's post, I think I have Canon DSLR noise PTSD and my mental 'smoothing' pendulum will tend to swing too far for a while!  But I'm glad you guys called it out so I can be more aware of it as I process my images. 

Yes, I definitely will only use dark-flats from now on.  I really just did both this last time to give it a try.  The dark-flats seem to work better with the ASI2600MC Pro.  And I completely agree not to use imaging time for darks and flats, if it can be helped!  I do my calibration frames the next day since I can duplicate the conditions (temperature, focus, filters) with the dedicated astro camera.  It makes life much easier and, perhaps more importantly, it allows more of the precious imaging time to be devoted to light subs!

Thanks so much again for the advice and tips, Terri!  I appreciate it.

Greg


   
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Terri Zittritsch
(@terri)
Member - Treasurer
Joined: 3 years ago
Posts: 165
 
Posted by: @greg-erianne
Posted by: @terri
Hi Greg, nice capture.     Colors are hard to tease out of galaxy photos (a lot are really difficult).     On this, one thing I'm seeing is a heavy hand in noise reduction.   Is this true?      The center of the galaxy is not blown out that much.  You could have exposed a bit less to keep the blown out center less exposed.   3 Min looks like enough to blow out the stars as well.    On Dark-Flat and Bias, you shouldn't need both.     The thinking for some time now has been that dark-flats (to calibrate darks) is all you should need for a CMOS camera along with your darks and flats, and you should only need it for each exposure time/gain/temperature and then create a library over time and just re-use them.     Darks is the same way, create a library and then re-use.   I never take darks and or dark flats in my imaging time.     But Flats as you know need to be taken before you rotate the camera on the scope.     You may get some more detail in there due to lower exposure, but the thing that jumps out at me is the softness of the galaxy, especially along the front edge.

Thanks for taking a look, Terri!  Yes, guilty of the heavy hand.  As I said (confessed) in reply to Paul's post, I think I have Canon DSLR noise PTSD and my mental 'smoothing' pendulum will tend to swing too far for a while!  But I'm glad you guys called it out so I can be more aware of it as I process my images. 

Yes, I definitely will only use dark-flats from now on.  I really just did both this last time to give it a try.  The dark-flats seem to work better with the ASI2600MC Pro.  And I completely agree not to use imaging time for darks and flats, if it can be helped!  I do my calibration frames the next day since I can duplicate the conditions (temperature, focus, filters) with the dedicated astro camera.  It makes life much easier and, perhaps more importantly, it allows more of the precious imaging time to be devoted to light subs!

Thanks so much again for the advice and tips, Terri!  I appreciate it.

Greg

Hi Greg, glad it's helpful as it is my intent.    Doing AP is hard, so any efforts are worth positive feedback.  But constructive feedback is useful.   I like it as my images are  far from perfect and I have lots of learning to do.  I get burned out and take breaks from spending so much time at the computer.    I've been playing with planetary but I have to admit, Vermont is not the best place to try to get good planetary images (at least not where I am).  I'll post my attempts soon.  I was out on the day before and day of Saturn opposition, as well as this past Friday and Saturday.  And even though we didn't have full jetstream, my seeing was still quite bad.  

 

Terri


   
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