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'first' image


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Hi all,

So it's not really my first image, but it's the first one since I upgraded from a barn door to a star adventurer.  The barn door was fun to build, but took a long time to setup and with two little ones about I need something a little quicker to setup and take down.

The star adventurer is my first real investment in astrophotography. I'm using a Canon 350d DSLR and a 75-300mm lens which I already had, so I wasn't expecting anything fantastic but I'm pretty pleased with the final result, even if there is plenty of room for improvement in data acquisition and processing. 

Here it is (yet another newbie takes a pic of M42)

Final.thumb.jpg.665506b3b114339e883e8f471b03fc0f.jpg

Approx 500 X 30sec exposures over three nights stacked with flats and bias (bias used as darks) in Siril.

After I applied background extraction, and photometric colour calibration I noticed some strange vertical colour banding on the image. Not sure what's causing this or if anyone has any ideas?  I've tried a different set a flats but it's still present and if I take only a single nights data it's still present. I managed to remove it during the histogram stretch, but without the banding I would have probably got more detail. 

Thanks for looking, just wanted to finish by saying thanks for everyone help with previous questions, you really are a very helpful and knowledgeable bunch. Also Siril is great!

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Here is a snapshot of the autostretched image showing the coloured bands on the image. 2022-01-16T14_06_50.png.a23cad1ecc364078b11a64673537a107.png

Happy to upload any other files if anyone thinks they would be useful in diagnosing the problem. 

Thanks

 

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Hi

Nice shot.

A few bits:

- Use bias as bias or simply enter the median bias value in the bias field.

- Dither between frames

- Use Siril's banding reduction on each frame after pre-processing. Then register the un-banded sequence.

- Stack using sigma clip at say, 3,3.

HTH

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Don't think this shot is that bad to be honest...I remember my first images using a Star Adventurer and a Canon DSLR and the thrill of seeing these deep sky wonders appear on my screen after a night of photography.

I think one of the biggest contributions to improving image quality is dithering. It virtually eliminates the background noise...When I got my HEQ5 Pro mount and started dithering I was just amazed at the improvement.

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Nice picture, I havent gotten around to trying orion myself yet, hopefully soon!

Perhaps a noob question; what is with the spike effect on the very bright stars? I can't recall seeing it like that before with so many, are they diffraction spikes? 

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Hi,

Thanks for the nice comments.

@alacant sorry if my description wasn't clear, I used the bias frames for bias and dark. I think this is what was recommended for Canon DSLRs?  Although I could have misunderstood. 

I will try the banding reduction in Siril, but might be a few days before I get chance to have a go.  Also 500 subs takes a long time to stack. 

I don't have guiding so don't think I can dither?  Although I probably have a fair amount of 'natural' dither from a fairly poor polar alignment due to no direct line of sight to Polaris.

@Sterrenland it's great when these objects start to come out of the dark. The reaction from my wife when she saw the stacked image on the computer was 'its amazing what you can see that from our garden'.

@RoloFanatic they are from the way the aperture closes is a camera lens. The 'classic' 4 spikes are from the secondary mirror supports on a newtonian reflector. 

@Astro Noodles it think it was the 4,5,7th Jan. That run of decent night's after all the cloud. No mods just stock. 

@Elp yes liking the wide field, might go a bit wider next time. I guess that's why the samyang 135 is so popular, and I'm very tempted to invest in one. 

Thanks again

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9 hours ago, Swillis said:

used the bias frames for bias and dark

Use the bias as bias. Don't use a dark of any description. Lose any script you maybe using which forbids you to do such; much better when the operator rather than the computer is in control! Get to know Siril manually.

9 hours ago, Swillis said:

don't think I can dither

Nudge each axis a little between every say three frames.

9 hours ago, Swillis said:

'natural' dither from a fairly poor polar alignment

For this to be effective it is best (essential?) to move the camera relative to the sky abruptly between frames, not constantly during them.

Cheers and good luck.

or2.jpg.bea488b9934804ae72b31119187a6bc8.jpg

 

Edited by alacant
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9 hours ago, Swillis said:

Hi,

Thanks for the nice comments.

@alacant sorry if my description wasn't clear, I used the bias frames for bias and dark. I think this is what was recommended for Canon DSLRs?  Although I could have misunderstood. 

I will try the banding reduction in Siril, but might be a few days before I get chance to have a go.  Also 500 subs takes a long time to stack. 

I don't have guiding so don't think I can dither?  Although I probably have a fair amount of 'natural' dither from a fairly poor polar alignment due to no direct line of sight to Polaris.

@Sterrenland it's great when these objects start to come out of the dark. The reaction from my wife when she saw the stacked image on the computer was 'its amazing what you can see that from our garden'.

@RoloFanatic they are from the way the aperture closes is a camera lens. The 'classic' 4 spikes are from the secondary mirror supports on a newtonian reflector. 

@Astro Noodles it think it was the 4,5,7th Jan. That run of decent night's after all the cloud. No mods just stock. 

@Elp yes liking the wide field, might go a bit wider next time. I guess that's why the samyang 135 is so popular, and I'm very tempted to invest in one. 

Thanks again

Considering the equipment you used, you should be very pleased with this.

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@alacant thanks for all the tips. I have started looking into using Siril manually so hopefully better results will be on their way. Was that image using the snapshot I posted?  Goes to show how valuable experience is in processing. 

I tried using per sub background extraction. Is this usually a good idea?

@Astro Noodles yes, I am pleased with it 👍

Thanks

 

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26 minutes ago, Swillis said:

using the snapshot I posted

Yes. I applied banding and green reduction.

26 minutes ago, Swillis said:

per sub background extraction

I've no hands on experience with a 350, but generally not a good idea -for us at least- as directly after stacking we pass the processing to StarTools where anything even slightly non linear just doesn't go.

But hey, to get anywhere near with a 15 year old camera and the 75-300 is going some. To get something as good as you have, amazing.

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Thanks for all the advice @alacant, I've finally had chance to finish reprocessing this and its looking better now. HH is definitely clearer now. 

M42-final-debanded.thumb.jpg.a09d131aeba2fe9dc0c2aac1a24964bc.jpg

The debanding worked well before stacking, but it didn't cope with the Orion nebula well as there were dark vertical bands above and below it but another round of debanding on the stacked image appeared to sort that out. 

The manual processing was easier than I thought, and will use it again in the future. 

Thanks again!

 

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