15 replies to this topic

[suresh_nikon]

Hi,

 

I recently photographed M101 on Sunday morning, with my NIKON D750 & Celestron C6-n (750 mm). There was a quarter moon west of the target which washed the images with a lot moon glare, unfortunately I could not shoot on the previous weeks due to cloudy skies. Most of the shoot went well and I was able to take 50 x 2 mins subs of the target, plus 30 Darks, 20 flats and 20 Biases. I did the post processing in Siril (v 1.2.0-beta2) and GIMP (v 2.10.34) but I am having issues with removing the gradient from the stacked image. Attached is the Autostretched image, after doing the photometric color calibration and background extraction, the image has not yet been stretched.. I am not sure how to remove or reduce the bright  areas on either side of the image.

 

I tried gradient tool in GIMP without much success.

thanks,

 

Suresh

 

Attached Thumbnails

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[rj144]

Post your unstretched stack.

 

Also looks kind of like a reflection ring...

[suresh_nikon]

I have uploaded it to my google drive. Its just the stacked image in Siril without doing any more processing.

 

Here's the link

 

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

Edited by suresh_nikon, 29 May 2023 - 09:59 PM.

[Jim Waters]

It looks like you didn't do Flats.

[Robert7980]

Ouch, it’s doable but won’t be easy…. I don’t know much about the tools you’re using, and even with my tools I’d have to play with it until I found something that works. With circular gradients I’ve never had much luck though there’s always some residual left behind… The good news is the galaxy is mostly gradient free so I’d start by cropping as much of that mess off as you can then deal with what’s left… You might be in ok shape by just doing that… 

 

I feel your pain though I had almost 4 months straight with only full moon clear skies… 

Edited by Robert7980, 29 May 2023 - 10:34 PM.

[suresh_nikon]

I did.. this is the content of my master directory. It contains the pp_flat_stackd file.

 

 

   

Attached Thumbnails

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[rj144]

You definitely have something else going on that's not related to the moon:

 

 

That was done in GraXpert and just autostretched in Siril.

[suresh_nikon]

Is it related to WB oy my location which is in Bortle 7 skies?

[rj144]

It's probably related to your flats.

[Jim Waters]

Is it related to WB oy my location which is in Bortle 7 skies?

Not sure what's going on.  The image doesn't look like Flats were taken into account or was processed wrong.  I image at Bortle 8.5 and with the moon out to some degree without major issues.

 

https://flic.kr/p/2oCwRzt

https://flic.kr/p/2oCvmZk

Edited by Jim Waters, 30 May 2023 - 12:05 AM.

[matt_astro_tx]

Did your camera move in between the time you took your Lights and when you took your flats?

[EPinNC]

As others have suggested, make sure you apply your flats.

 

Remember that Siril has a very effective "Background Extraction..." tool under the "Image Processing" drop-down menu.  See the documentation.  But before you use that tool, crop your image to remove as much of the edge-related messiness as you can.

 

Also, the way those dust spots appear suggests to me that your dithering is not very random.  Those spots have a pattern extending from the lower left to upper right.

[suresh_nikon]

@matt_astro_tx: No I had left my camera connected to my telescope and then took the flats at dawn.

I found just now that it seems NINA took flats @ 800 ISO while the lights, darks & biases were taken @ 1600 ISO. Probably the reason for this.

 

Thanks for all your inputs. Hopefully in the coming weeks if the current weather holds in North Shore MTL then i will take jab at it again and maybe this time I take the flats properly

 

Although I would like to take the flats before I start the session during dusk. I am not sure if it will be proper, as cannot focus properly during the dusk as there are no far away landmarks visible from my backyard which I can use to achieve focus.. So I am not sure what could be done. Neither do I want wait for the next morning to take the flats, as I don't want to leave my camera outside in my backyard, as it could be easily accessed from outside.

 

 

 

thanks,

 

Suresh

Edited by suresh_nikon, 30 May 2023 - 11:30 AM.

[suresh_nikon]

@epinnc: I did not dither, my mount is CG-4 without guiding. It only has RA motor, plus for the DEC it has knobs and hence I am not keen on using the DEC knobs to dither.

 

I am saving up to either buy a new mount with Guiding like HEQ5 or convert this mount to proper guiding mount with products like EQStarEQ3 from Astrogadgets, but thats few months away.

[EPinNC]

@epinnc: I did not dither, my mount is CG-4 without guiding. It only has RA motor, plus for the DEC it has knobs and hence I am not keen on using the DEC knobs to dither.

 

I am saving up to either buy a new mount with Guiding like HEQ5 or convert this mount to proper guiding mount with products like EQStarEQ3 from Astrogadgets, but thats few months away.

I started out with some of the worst gear possible -- DSLR, Orion Apex 1300mm Mak-Cass telescope, and an Orion AstroView EQ mount:

 

 

Far, far too much focal length for that mount, and the mount only had an RA motor.  I was still able to dither by using the hand controller for RA and just-barely-touching the Dec knob.  I get your reluctance -- it's not easy.  I'm just saying that it's possible to do while you're saving/waiting for a better mount.  I was able to make these:

 

https://www.cloudyni...obular-cluster/

 

https://www.cloudyni...-lagoon-nebula/

 

https://www.cloudyni...23-iris-nebula/

[suresh_nikon]

I think its  flats i took with my white t-shirt which is probably the reason for the weird issues. I used an older white t-shirt to take the flats. I will probably need to buy a brand new one from the store. Today to test it out, I took the flats again using the T-shirt and then using a plain printer paper with the my other laptop as the screen. After which to test out I used the new flats and tested with the old data (just to see if there is any improvement), I saw the T-shirt still caused me the weird gradient, but white printer paper gave a slightly better result.

 

Thanks a lot for the replies and ideas.