NGC6888 Crescent Nebula by 120mc-s

firstc8

Stacked 730 good light frames and 100 darks @4s tonight before clouds moved in. The camera seems to have reached its limit on what can be reasonably captured.

betacapricorni

Good shot! Try with a softest elaboration. Unguided?

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firstc8

betacapricorni wrote:
Good shot! Try with a softest elaboration. Unguided?

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No guider yet.

I had only two hours of window last night between storms to setup and shoot this one, wanted to compare to the one I did a few nights ago (Crescent.jpg) when seeing condition was worse. Below are two processed in different seeing conditions. Even in bright moonlight, last night's better seeing condition clearly showed (Crescent3.jpg) how much further I could stretch without too much noise.

I did processed it softer this time, even tried to use star mask to prevent over blown stars but without success. I guess you are limited to the quality of the raw image.

riklaunim

Post a raw TIFF/FITS stack and I'll check those stars :)

firstc8

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riklaunim

ZIP it and then dropbox or alike if it doesn't uploads here.

firstc8

Tried several zip programs, still 10mb file. I can email you if you PM me. No Dropbox for me yet.

I also opened your file in Photoshop using Liberator plug, but it is a mono file, very different than the RGB files I have worked so far. Besides, my file is captured with very narrow FOV. I'd prefer you take a look at it and let me know what might be the issue.

I certainly hope it is a process issue. Getting a mono camera and filter wheel is still too much learning curve for me at this time.

Thanks!

firstc8

Processed these raw frames using PixInsight trial version and got this result.

riklaunim

The stars on that image aren't round (and in perfect focus). That also lowers the quality of captured nebulosity. Field analysis shows how bad it is:

Clipboard01.jpg

Bad focal reducer, bad collimation, bent imaging chain can cause that.

betacapricorni

Unguided?

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elmerfudd

riklaunim wrote:
The stars on that image aren't round (and in perfect focus). That also lowers the quality of captured nebulosity. Field analysis shows how bad it is:

Clipboard01.jpg

Bad focal reducer, bad collimation, bent imaging chain can cause that.

Interesting.How did you produce this field analysis picture? Can you elaborate on what it's showing?

firstc8

riklaunim wrote:
The stars on that image aren't round (and in perfect focus). That also lowers the quality of captured nebulosity. Field analysis shows how bad it is:

Clipboard01.jpg

Bad focal reducer, bad collimation, bent imaging chain can cause that.

Thanks for the image, is it the entire frame?

I collimated the scope but only at the center of the frame. With the Celestron F6.3 the edges of the frame were clearly a bit off, and stacked a generic 0.5 reducer after that so it could only be worse. The tinny sensor does make such arrangement tolerable.

Yes it was also unguided, but I was doing lucky imaging so that should not be the main culprit. In fact after I stacked all 253 good lights, the final image did not even need cropping.

firstc8

On second close inspection, I noticed the previous image (Crescent3) has more uniform star color and better focus. But the last two images were from the same batch of Lights/darks/biases. Only "Crescent3" was stacked in DSS and processed in PS, and the last image was stacked and processed in PI. I even went back to compare the two stacked raw frames (before post processing), and they looked very much identical.

The PI processed image (the last one) has color shift in the stars and focus was off too, need to figure that out. I simply followed a few PI processing tutorials to process that last one.

riklaunim, could you do an analysis of "Crescent3" too? There could be things PS and PI did differently during post processing. If true I will have to ask PI about that. Thanks!

riklaunim

That "generic" 0.5 reducer trashes you image quality. Previous stacks just try to align on that comatic star shapes and you got very big stars and fuzzy nebulosity.

The field quality image is from CCD Inspector.

firstc8

riklaunim wrote:
That "generic" 0.5 reducer trashes you image quality. Previous stacks just try to align on that comatic star shapes and you got very big stars and fuzzy nebulosity.

The field quality image is from CCD Inspector.

With only the Celestron F6.3 I could not get good focus with my average seeing. In fact last night I did try it on M1 with my new mono and Ha narrow band, this time I even had PHD guiding. Stars were difficult to focus. DSS or PI could not even stack the images.

I hope to have better and more stable seeing soon to try again, but I suspect for practice will have to do with F6.3 and F5 stacked for now. I can live with curvatures at this moment, main thing now is to learn LRGBHa imaging basics.

riklaunim

There are SCT f/3.3 focal reducers for sensors up to 1/3" - so ASI120. The 0.5 makes the image quality really bad and you will be wondering why it doesn't look like it should ;)

firstc8

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firstc8

BTW stacking 6.3 and 0.5 had improved raw mono images greatly. I have two more imaging sessions before processing all my raw LRGBHa files. Will find out how the 0.5 reducer works in the mono setup.

I might have more flexibility to play with the mono channels to minimize the curvature effects from the reducer stacking.

firstc8

Well, the generic 0.5 reducer continues to show severe curvature all the way to the near center of the frame. My backyard seeing conditions also limit the resolution. But HaGB color combination does show the potential when I can get to a dark site:

riklaunim

You could try Nebulosity, even trial version, and align the HaRGB frames against each other using 2-stars with rotation alignment type. That should help as some seems to not align perfectly. But in general the nebulosity is there. And sometimes H-alpha as mono will look just better than a color variant with H-alpha channel. ;)