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Galaxy Imaging in Red Zone

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#1 Kisslija

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Posted 20 September 2020 - 04:28 PM

I'm looking for some input regarding imaging in heavy light pollution. I'm in a suburb of St. Louis, Bortle class 8. When I use narrow band filter (L-Enhance), I'm able to get fairly good clean images with my ASI294MC Pro, Hyperstar and C9.25, even when the moon is out. Obviously with that filter, I'm shooting emission nebula.

 

The issues come when I attempt to shoot galaxies with the Optolong L-Pro filter, which I realize is broadband. I've attached two images. Both were captured as raws in SharpCap and stacked, integrated and registered in Pixinsight with corresponding darks and flats (25 of each). The greenish image is stretched, but untouched otherwise. The other image has only been run through the dynamic background extraction in Pixinsight to remove the light pollution and gradients. If you look at the image it's blown out in the middle. This is happening with both short subs (20 seconds) and longer subs (120 seconds). The attached images I took last night with no moon, 120 second subs with a total integration time of 136 minutes. My issue is that it's too blown out to process and when I attempt to clean it up I end up destroying the galaxy.

 

When I run the Smart Histogram feature in SharpCap it indicates that based on my sky conditions and imaging set-up, I should shoot 20 second subs. I run into the same issue when I drop the subs to 20 seconds.

 

Is this normal in heavily light polluted areas or are my calibration frames not working properly? When I look on Astrobin, I see people in heavily light polluted areas getting good images with color cameras. I don't get it.

 

Any insight would be welcome.

 

 

Attached Thumbnails

  • M33-120second subs-136minute total integration-Raw Stack Small.png


#2 Kisslija

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Posted 20 September 2020 - 04:35 PM

Image with DBE performed in Pixinsight:

 

   

Attached Thumbnails

  • M33-120second subs-136minute total integration- Raw Stack- Pixinsight DBE Small.png


#3 Midnight Dan

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Posted 20 September 2020 - 04:51 PM

Not sure what you mean by "blown out in the middle".  Usually, blown out means an image is overexposed to the point of clipping so that all detail is lost in that area.  Your image doesn't appear blown out to me.

 

Are you referring to the heavy gradient from dark at the edges to lighter in the middle?  If so, my guess is that your flats are not working for some reason.  They should eliminate that.

 

-Dan



#4 mborland

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Posted 20 September 2020 - 04:54 PM

I found this video very helpful

https://www.youtube....h?v=vYcssQitw4U

 

After following many of the steps in the video, I was able to get this image using 126 minutes of data from my Bortle 8 driveway.

FireworksGalaxy-LX90Red-126min-sm.jpg

Bigger, higher-resolution version is here

https://www.flickr.c...N07/50365332017

I'm pretty happy with it.

 

I used an 8" SCT, 0.65 reducer, and L-Pro filter. I couldn't see much of anything on the individual subframes as I collected the data, so I gave up and switched to another target. Now I know better.

--Michael

 



#5 nimitz69

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Posted 20 September 2020 - 05:01 PM

So I’m the last guy to give PI processing advise but 2 hrs doesn’t seem like a lot of time for Bortie 8 skies. Also, there is usually a lot of PI wizardry required in Heavy LP to produce those great image you see ...

I’m sure a real PI expert will. Be along eventually to tell you what you need to do ...

#6 mborland

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Posted 20 September 2020 - 05:40 PM

So I’m the last guy to give PI processing advise but 2 hrs doesn’t seem like a lot of time for Bortie 8 skies. Also, there is usually a lot of PI wizardry required in Heavy LP to produce those great image you see ...

I’m sure a real PI expert will. Be along eventually to tell you what you need to do ...

The image I showed above (and the better image on flickr) is from just over two hours of imaging with no moon. More would be better, but it isn't so bad in my opinion.

 

--Michael



#7 Lead_Weight

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Posted 20 September 2020 - 06:30 PM

All the galaxies on my site were shot in bortle 7/8 skies. https://www.macobser...m/image-gallery

 

The main thing you need to do is not overexpose the images. It's easy to flood the image with light pollution. So you have to shoot under the light pollution ceiling. I tend to expose at 0 gain for the highest dynamic color range and keep frame exposures that are 1-2 minutes. I shoot around 7-10 hours for each galaxy. Basically a full night on a single target. You'll need lots of time to overcome the effects of the poor quality skies.

 

Then you need good calibration frames, and to understand the best way to remove light pollution with software. I've used PixInsight and Astro Pixel Processor, and the latter does a much better job removing light pollution. Here's a tutorial I wrote at doing this. https://www.macobser...pixel-processor  Try the free trial if you want to experiment before considering a purchase.

 

Good luck....It can be done.


Edited by Lead_Weight, 20 September 2020 - 06:36 PM.


#8 sn2006gy

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Posted 20 September 2020 - 06:36 PM

It almost looks like your subs were over corrected on calibration. I shoot with an L-PRO and i haven't had any issues with DBE and processing.  I may come back during new moon to re-shoot some stars if i lost some color but that's about it.



#9 Kisslija

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Posted 20 September 2020 - 11:29 PM

I sincerely appreciate everyone sharing their thoughts! Learning AP has been both challenging and rewarding and at times, frustrating. However, I love it!

 

Not sure what you mean by "blown out in the middle".  Usually, blown out means an image is overexposed to the point of clipping so that all detail is lost in that area.  Your image doesn't appear blown out to me.

 

Are you referring to the heavy gradient from dark at the edges to lighter in the middle?  If so, my guess is that your flats are not working for some reason.  They should eliminate that.

 

-Dan

Poor choice of words on my end. Your assumption was correct, my comment was meant to imply the heavy light gradient in the middle. I'm wondering if I need to re-shoot my flats with the white peak in the lower part of the histogram. When I originally shot them I made sure everything remained the same in my imaging train and the white peak was at about 50% in the histogram.

 

I found this video very helpful

https://www.youtube....h?v=vYcssQitw4U

 

After following many of the steps in the video, I was able to get this image using 126 minutes of data from my Bortle 8 driveway.

attachicon.gifFireworksGalaxy-LX90Red-126min-sm.jpg

Bigger, higher-resolution version is here

https://www.flickr.c...N07/50365332017

I'm pretty happy with it.

 

I used an 8" SCT, 0.65 reducer, and L-Pro filter. I couldn't see much of anything on the individual subframes as I collected the data, so I gave up and switched to another target. Now I know better.

--Michael

Appreciate the link, I'll take a look and see if I can learn something new smile.gif . YouTube has been great to learn Pixinsight.  I like the fact that you were able to get some color out of your image with relatively short integration. The image is great, thanks for sharing!

 

 

 

So I’m the last guy to give PI processing advise but 2 hrs doesn’t seem like a lot of time for Bortie 8 skies. Also, there is usually a lot of PI wizardry required in Heavy LP to produce those great image you see ...

I’m sure a real PI expert will. Be along eventually to tell you what you need to do ...

I'm just now coming to terms with the reality of how long the total integration time has to be in order to get decent images using a OSC camera in Bortle 8 skies frown.gif . Shooting the nebulas with narrow band filters has definitely been less of a challenge.

 

All the galaxies on my site were shot in bortle 7/8 skies. https://www.macobser...m/image-gallery

 

The main thing you need to do is not overexpose the images. It's easy to flood the image with light pollution. So you have to shoot under the light pollution ceiling. I tend to expose at 0 gain for the highest dynamic color range and keep frame exposures that are 1-2 minutes. I shoot around 7-10 hours for each galaxy. Basically a full night on a single target. You'll need lots of time to overcome the effects of the poor quality skies.

 

Then you need good calibration frames, and to understand the best way to remove light pollution with software. I've used PixInsight and Astro Pixel Processor, and the latter does a much better job removing light pollution. Here's a tutorial I wrote at doing this. https://www.macobser...pixel-processor  Try the free trial if you want to experiment before considering a purchase.

 

Good luck....It can be done.

OMG, your images are amazing! I'm shooting the Wizard Nebula as I type this out and came across your image on AstroBin about 30 minutes ago, too funny! I'm blown away you're able to get those types of images in Bortle 7 skies.

 

I typically always keep the gain setting at 120 as that's where it hits unity. It never occurred to me to drop it to zero. I would ask if you notice much of a difference but I think your pictures say everything, I'll give it a shot. My biggest problem is I get too excited to shoot multiple objects in the same night. I need to pick one target and dedicate all the time that night to said object. My favorite targets are galaxies and would really like to capture some good data. 

 

Is your scope on a fixed mount? I've never captured images of the same target on multiple nights. I take my scope and mount in the garage every night. If I mark the driveway and set-up the mount in the exact same spot and perform a new alignment, I'm assuming a could integrate data from multiple nights. Is my assumption correct?



#10 Jeff2011

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Posted 21 September 2020 - 12:13 AM

Sure you can integrate data from multiple nights.  When imaging in light pollution you pretty much need to.  Different areas of your sky may be darker than others so you may need to limit your data acquisition to those areas and image multiple targets in a night as they pass through those areas and collect multiple nights worth. When I imaged from my backyard it was not uncommon to collect four or five nights worth of data on a target.  However if you really like galaxies, I recommend getting access to a dark site.  Many clubs have one and the quality of data at a dark site is so much better.



#11 Kisslija

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Posted 21 September 2020 - 12:29 AM

Sure you can integrate data from multiple nights.  When imaging in light pollution you pretty much need to.  Different areas of your sky may be darker than others so you may need to limit your data acquisition to those areas and image multiple targets in a night as they pass through those areas and collect multiple nights worth. When I imaged from my backyard it was not uncommon to collect four or five nights worth of data on a target.  However if you really like galaxies, I recommend getting access to a dark site.  Many clubs have one and the quality of data at a dark site is so much better.

Is it an issue integrating the images from different nights without a fixed mount? If not, how exact does the placement have to be? Is there a certain timeframe the images need to be within? i.e. within a few days or can it be spread over over a week or two if sky conditions will not cooperate?



#12 Jeff2011

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Posted 21 September 2020 - 12:50 AM

You can integrate images from nights years apart.  Usually galaxies are smaller so the framing does not need to be that close. Even the camera angle don’t matter so much as registration aligns all frames to a reference image however it is best if you leave your camera attached to the scope at the same camera angle. Less rotation by registration results in less distortions and cleaner data.  
 



#13 Lead_Weight

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Posted 21 September 2020 - 07:42 AM

OMG, your images are amazing! I'm shooting the Wizard Nebula as I type this out and came across your image on AstroBin about 30 minutes ago, too funny! I'm blown away you're able to get those types of images in Bortle 7 skies.

 

I typically always keep the gain setting at 120 as that's where it hits unity. It never occurred to me to drop it to zero. I would ask if you notice much of a difference but I think your pictures say everything, I'll give it a shot. My biggest problem is I get too excited to shoot multiple objects in the same night. I need to pick one target and dedicate all the time that night to said object. My favorite targets are galaxies and would really like to capture some good data. 

 

Is your scope on a fixed mount? I've never captured images of the same target on multiple nights. I take my scope and mount in the garage every night. If I mark the driveway and set-up the mount in the exact same spot and perform a new alignment, I'm assuming a could integrate data from multiple nights. Is my assumption correct?

Thanks! I too was super excited when I started out, trying to get as many images as I could every night. But since then I've started to focus on getting quality images. My scope isn't fixed either, and I have to break it down and put it back up every time I image. If I have a string of clear nights, I leave it out in my back yard during the time to keep from having to set it up again each night. 

 

As others have said, you can integrate data from multiple nights, even across years. Astro Pixel Processor makes this pretty easy as you can load each set of data (lights, flats, darks) as a session, and integrate multiple sessions. I wrote a tutorial on doing this. https://www.macobser...maging-sessions




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