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Siril? Help?


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Hi everyone 

 

last night I took 30x30sec exposures. 
 

i was hoping to capture the horsehead nebula and the flame nebula. 
 

ive tried to edit in siril but I keep getting these huge grey marks on the photo. Any advice 

 

this is after background removal and green removal

9AA4CBD2-77B9-4C29-AE50-BC222FA39FB3.jpeg

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I'm far from being an expert but, are you using flat frames for image calibration? Surely they will help. 

Before background and green removal I crop the image and do a photometric color calibration. After that, do the background and green noise removal and then I move to Photoshop for the non-linear post processing. 

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28 minutes ago, barbulo said:

I'm far from being an expert but, are you using flat frames for image calibration? Surely they will help. 

Before background and green removal I crop the image and do a photometric color calibration. After that, do the background and green noise removal and then I move to Photoshop for the non-linear post processing. 

Ah that must be it! Lol. The flat frames I took are just pure light. Is that incorrect ?

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Take them with the same gain/ISO as the light frames and a exposure time such that the peak of the histogram is between 1/3 and 1/2 (mid-left). Put a white t-shirt or blanket and point the telescope to an even source of light (light panel or tablet screen with white background). Take between 20-30. 

They may appear white or light gray or blue, depending on your camera and filters. If you stretch a valid flat you will see some kind of gradient. If you overexpose or underexpose those, they won't help you that much.

Moreover, depending on your camera, you might need dark and bias frames as well.

HTH.

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Flat frames must be taken maintaining the very same optical path as the light frames: same camera position, same filters, same focus position...  Otherwise, they are useless. Normally are taken at the end of the imaging session.

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That is much better, but still not ideal. You could probably crop that and use the "eye dropper tool" in levels in PS to even out the background well enough.

Perhaps try without any flats at all, might give you a better start to work with.

Also, Im not a pro with the background extraction in Siril, but I do find it can be very harsh I think..The default is set to 4 and that will do all kinds of weird to my images usually, try 1-2, these tend to be a bit more subtle if I remember correctly. Good luck :)

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Looks a bit like light leak from the viewfinder if you used a DSLR. The viewfinder is a light pathway to the sensor and some light will leak there if its not blocked.

On my first session out with a DSLR i had a red light headlamp on pretty much the whole night and occasionally i would point it towards the camera. It left a red blotch on all the frames that looks a lot like what you have here. This would not be removable with flats and would conveniently explain why the weird shape remains after taking flats. Or could just be that the flats you took were not that great, so how did you take the flats?

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48 minutes ago, barbulo said:

Flat frames must be taken maintaining the very same optical path as the light frames: same camera position, same filters, same focus position...  Otherwise, they are useless. Normally are taken at the end of the imaging session.

Oh. I’ve read that you can take flat frames by pointing the telescope at the sky and covering the scope with a T-shirt ?

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19 minutes ago, Iem1 said:

That is much better, but still not ideal. You could probably crop that and use the "eye dropper tool" in levels in PS to even out the background well enough.

Perhaps try without any flats at all, might give you a better start to work with.

Also, Im not a pro with the background extraction in Siril, but I do find it can be very harsh I think..The default is set to 4 and that will do all kinds of weird to my images usually, try 1-2, these tend to be a bit more subtle if I remember correctly. Good luck :)

I didn’t know I could do it without flat frames in siril?

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8 minutes ago, ONIKKINEN said:

Looks a bit like light leak from the viewfinder if you used a DSLR. The viewfinder is a light pathway to the sensor and some light will leak there if its not blocked.

On my first session out with a DSLR i had a red light headlamp on pretty much the whole night and occasionally i would point it towards the camera. It left a red blotch on all the frames that looks a lot like what you have here. This would not be removable with flats and would conveniently explain why the weird shape remains after taking flats. Or could just be that the flats you took were not that great, so how did you take the flats?

I took the flats by pointing the scope at the sky and covering it with a white T-shirt. I used AV mode. Same iso. Camera determined shutter speed 

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4 minutes ago, Jjmorris90 said:

I took the flats by pointing the scope at the sky and covering it with a white T-shirt. I used AV mode. Same iso. Camera determined shutter speed 

Can you attach the raw flat file so i could have a look?

That is a good method by the way, unless the sky was somehow unevenly lit at the time. AV mode in DSLRs always produced decently illuminated flats for me so i wouldn't worry about the method. But if you want to test another method you can just point the camera and telescope (or lens or whatever) to a computer screen/tv/tablet that is showing a white screen with the minimum brightness setting. Take at least 30 flats and move the telescope around the screen and rotate it in your hands during this to make any possible defects in the screen even out in stacking.

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4 minutes ago, Jjmorris90 said:

sure. here is one of the flats. 

IMG_2741.CR2 24.59 MB · 1 download

No problems with the flat. Nicely illuminated with no overexposed pixels at all. There are some 0-value pixels in the red channel but i dont think its the issue here. Not sure how to go about fixing that either, maybe trying to take a longer exposure flat by dimming down the light source since this is a 1/200s flat exposure? A couple of T-shirt layers more with sky flats or the monitor method with a dimmable light source, but anyway thats beside the point.

2022-01-09T15_57_32.thumb.png.ef0996a383397affdf7cf54e74b9f69c.png

You get this view in Siril by putting the preview mode to "Histogram" in the bottom and selecting the rainbow false color mode from the bottom tool panel. Very easy to see what is what especially with flats. This is a pretty good flat although the optical axis is not exactly center to the camera (collimation or tilt).

Do you get the gray uneven blotches on the raw stack before background extraction?

Ill go with either a) light leaks during capture (difficult to remove) or b) something wrong with the background removal process.

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Difficult to tell from the screenshot if something is wrong, can you post the raw stack?

Im banking towards background extraction going wrong. I use Siril a lot and sometimes its just difficult to use and should be done on the individual subs before stacking. There is a method to do this in Siril with the seqsubsky console command but i would like to try on the stack first if thats ok.

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3 minutes ago, ONIKKINEN said:

Difficult to tell from the screenshot if something is wrong, can you post the raw stack?

Im banking towards background extraction going wrong. I use Siril a lot and sometimes its just difficult to use and should be done on the individual subs before stacking. There is a method to do this in Siril with the seqsubsky console command but i would like to try on the stack first if thats ok.

sure, here. 

thank you :) 

result.fit

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9 minutes ago, Jjmorris90 said:

sure, here. 

thank you :) 

result.fit 207.18 MB · 0 downloads

The gradient is blotchy and difficult to remove. I end up with a similar result as you with most methods. I could probably brute force this with GradientXterminator plugin in Photoshop, but it looks difficult to deal with. Looks a lot like a light leak to the sensor somehow IMO. Also since you are using a newtonian it is possible your collimation has changed since shooting the lights and taking the flats, which is why flats are best taken straight after the session.

Canon5DViewfinder001.jpg?resize=470,185 This needs to be blocked so that no light can enter during shooting. It could be the culprit here.

But one more thing you can try other than re-shoot the frames is to do the background extraction per sub. This works well for linear gradients, but if each sub has a nonlinear gradient due to light leaks it may not work that well.

To do this you should use the "seqsubsky" command in Siril before stacking. After pre-processing you can run this command by inputting "seqsubsky pp_light 1" to the console. In here seqsubsky is the command, pp_light is the sequence name in question and 1 is the degree order of the extraction. 1 is linear 2 is less linear etc, usually only the first order extraction works well for individual subs.

If you used one of the scripts built in to Siril to do the whole process you can add the command line in to the script you used. You can open the .SSF files with Windows word pad.

script.PNG.e4f78ed44a7a85c9391b7d0e79deeb4b.PNG

I am not quite sure to which point the command goes, but it might be the one i marked.

An easier way (which i use) would be to use Sirilic, a software that uses Siril for stacking but makes all the data usage much simpler with a drag and drop interface. No need to manually faff with folders with Sirilic.

Here: https://siril.org/docs/sirilic/#download

 

sirilic.PNG.20f1557cfe884407b7896ed86aee54ed.PNG

In Sirilic the "subsky" command does the background extraction per sub. Set to 0 for no extraction, 1 for linear extraction. Higher than 1 will probably not work well but you could always try.

Its a lot to think about, sorry if it sounds like im rambling 😅

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4 minutes ago, ONIKKINEN said:

The gradient is blotchy and difficult to remove. I end up with a similar result as you with most methods. I could probably brute force this with GradientXterminator plugin in Photoshop, but it looks difficult to deal with. Looks a lot like a light leak to the sensor somehow IMO. Also since you are using a newtonian it is possible your collimation has changed since shooting the lights and taking the flats, which is why flats are best taken straight after the session.

Canon5DViewfinder001.jpg?resize=470,185 This needs to be blocked so that no light can enter during shooting. It could be the culprit here.

But one more thing you can try other than re-shoot the frames is to do the background extraction per sub. This works well for linear gradients, but if each sub has a nonlinear gradient due to light leaks it may not work that well.

To do this you should use the "seqsubsky" command in Siril before stacking. After pre-processing you can run this command by inputting "seqsubsky pp_light 1" to the console. In here seqsubsky is the command, pp_light is the sequence name in question and 1 is the degree order of the extraction. 1 is linear 2 is less linear etc, usually only the first order extraction works well for individual subs.

If you used one of the scripts built in to Siril to do the whole process you can add the command line in to the script you used. You can open the .SSF files with Windows word pad.

script.PNG.e4f78ed44a7a85c9391b7d0e79deeb4b.PNG

I am not quite sure to which point the command goes, but it might be the one i marked.

An easier way (which i use) would be to use Sirilic, a software that uses Siril for stacking but makes all the data usage much simpler with a drag and drop interface. No need to manually faff with folders with Sirilic.

Here: https://siril.org/docs/sirilic/#download

 

sirilic.PNG.20f1557cfe884407b7896ed86aee54ed.PNG

In Sirilic the "subsky" command does the background extraction per sub. Set to 0 for no extraction, 1 for linear extraction. Higher than 1 will probably not work well but you could always try.

Its a lot to think about, sorry if it sounds like im rambling 😅

Aha i will give it a Go. Thanks for looking. 
 

il block the viewfinder next time. And how can I take flats at night? 
 

thanks 

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36 minutes ago, Jjmorris90 said:

Aha i will give it a Go. Thanks for looking. 
 

il block the viewfinder next time. And how can I take flats at night? 
 

thanks 

Most folks use light panels of some sort. Its an extra trinket to carry out and set up but worth it in my opinion since flats are probably the most important type of calibration frame.

There are expensive options: https://www.teleskop-express.de/shop/index.php/cat/c229_Flat-Field-foils-and-boxes.html

And cheap options: https://www.amazon.co.uk/Drawing-Tracing-Ultra-Thin-Adjustable-Brightness/dp/B072F8T5FH/ref=sr_1_29?crid=12P09PNJDKODH&keywords=agptek+light+panel&qid=1641750123&s=kitchen&sprefix=agptek+light+panel%2Ckitchen%2C83&sr=1-29

I use the latter. These cheap drawing tracing tablets feel like toys and probably wont last long but they are very cheap and do the same thing. The dedicated flat field panels are dimmable to whatever level you want and some can work with capture software (like NINA) to automatically take the ideal flat exposure.

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