M42

Processing Deep Sky Artifacts
7 replies•264 views
Jerry Gerber avatar
Jerry Gerber avatar
Hi all,

This is my 2nd attempt at astrophotography.   I overexposed this image by taking 180s subs, next time I'll try 60s or 90s .  PI did a great job of getting rid of the satellites. 

There's a dark "smudge" in the mid-left area of photo.  What is this?   I can crop it out, but I'd like to understand what caused it and if there's a way in post to remove it.   I examined the original subs and it appears on all, or most, of them.  Might it have to do with flats?

Thanks to all!
Jerry
www.jerrygerber.com
Engaging
Jonny Bravo avatar
Jonny Bravo avatar
Very likely a dust mote on the filter or some other glass surface relatively close to the sensor. Your calibration frames should have taken care of it. I can see a number of other spots throughout your image, so you'll need to look into your calibration process to see what's going wrong.
Well written Helpful Respectful Concise
Jerry Gerber avatar
Jerry Gerber avatar
Jonny Bravo:
Very likely a dust mote on the filter or some other glass surface relatively close to the sensor. Your calibration frames should have taken care of it. I can see a number of other spots throughout your image, so you'll need to look into your calibration process to see what's going wrong.

Thanks Jonny.
Chase Newtson avatar
Chase Newtson avatar
My scope has had something similar to this, I believe they are actually on the telescopes objective based off the size and that light still slightly made it through. May be a smudge perhaps.   I've had dust motes land on something closer to the camera sensor and it is a much darker spot as it blocked more light, and in my case, larger amount of surface area.  

As for my scope when a few of these appeared, my flats worked great at removing it.  What camera did you use?
Jerry Gerber avatar
Jerry Gerber avatar
Chase Newtson:
My scope has had something similar to this, I believe they are actually on the telescopes objective based off the size and that light still slightly made it through. May be a smudge perhaps.   I've had dust motes land on something closer to the camera sensor and it is a much darker spot as it blocked more light, and in my case, larger amount of surface area.  

As for my scope when a few of these appeared, my flats worked great at removing it.  What camera did you use?

Hi Chase,

An ASI2600MC.  I took 30 flats the next morning, same image train, same filter, same bias, same temperature as the lights.  I calibrated them in PI and then integrated with a dark flat.  When I brought the telescope in the house after imaging that night, I noticed a dust ball or something next to the objective lens, but on the inside, there's no way to remove it without dismantling the scope, right?

Is there a way to remove this spot in post?   An ordinary photo editor like Photoshop (I actually use ACD Ultimate which I think is superior to Photoshop and with no subscription necessary) doesn't have the correct tools to do this.  What PI process would I try to remove it?

Jerry
Chase Newtson avatar
Chase Newtson avatar
Yes there is, you can create a synthetic flat frame. I currently use photoshop for my post processing.

I'll try to remember the best I can as I haven't had to use a synthetic flat in a while and I'm not home to double check I didn't miss a step.

In the image, I'd copy and paste into a new document to edit on that one.
 - first you'd want to remove the nebula and any exceptionally bright stars with the lasso tool, then fill with content aware, or use content aware tool
 - once it's just a field of smaller faint stars, use the "filter - noise - dust and scratches".  Edit the slider until the remaining stars fade away.  You should hopefully see where the blotches are still along with any gradients.
 - in the original image, go to "image tab - apply image", and in the menu box, select the copied image in the drop down and under blend mode: select "subtract"
 - level out the black point and so on.  

Hopefully this can help remove the blotches, and can also help with the gradient as well.  I know this is photoshop, but maybe it can roughly be translated to the program you use?
Helpful
Chase Newtson avatar
Chase Newtson avatar
Jerry Gerber:
Chase Newtson:
My scope has had something similar to this, I believe they are actually on the telescopes objective based off the size and that light still slightly made it through. May be a smudge perhaps.   I've had dust motes land on something closer to the camera sensor and it is a much darker spot as it blocked more light, and in my case, larger amount of surface area.  

As for my scope when a few of these appeared, my flats worked great at removing it.  What camera did you use?

Hi Chase,

An ASI2600MC.  I took 30 flats the next morning, same image train, same filter, same bias, same temperature as the lights.

In terms of the 2600, I have no experience (I have the 294MC Pro) but I believe it is better to use dark flats, and not take bias frames with that camera.  You can try to restack using the flats you took with dark flats and see if that produces a better result with removing the artifacts?
Jerry Gerber avatar
Jerry Gerber avatar
Chase Newtson:
Jerry Gerber:
Chase Newtson:
My scope has had something similar to this, I believe they are actually on the telescopes objective based off the size and that light still slightly made it through. May be a smudge perhaps.   I've had dust motes land on something closer to the camera sensor and it is a much darker spot as it blocked more light, and in my case, larger amount of surface area.  

As for my scope when a few of these appeared, my flats worked great at removing it.  What camera did you use?

Hi Chase,

An ASI2600MC.  I took 30 flats the next morning, same image train, same filter, same bias, same temperature as the lights.

In terms of the 2600, I have no experience (I have the 294MC Pro) but I believe it is better to use dark flats, and not take bias frames with that camera.  You can try to restack using the flats you took with dark flats and see if that produces a better result with removing the artifacts?

Yeah, I used dark flats to calibrate instead of bias frames.  Maybe I'll run through the whole process again and try different settings..I also substituted bias frames for dark flats, but the results were identical.  I think I need to learn how to create a synthetic flat in PI, or find the right process or processes, to remove the dust mote, or whatever it is..
Related discussions
Reflections (?) with all filters / images on QHY600M
Hi all, I posted previously about a "smudge" I was noticing on all of my flats with all filters. The smudge appeared to calibrate out in a few test images, so I went ahead and shot 40 hours of the Ghost of Cassiopeia. Unfortunately, after I...
Dark smudge on flats may relate to reflections issue discussed.
Oct 27, 2024
Artefacts in registered images....what am I missing????
Hi All I am imaging a dusty region, and when stacking, I can see that my flats have not correctly removed a particular artefact. Any input on what I might be missing here?? I cannot understand what I am not doing correctly to prevent this annoying ar...
Flats not removing artifacts; directly addresses your calibration frame problem.
Nov 28, 2024