Galaxy is not sharp - Forums

Topic starter

Apr 7, 2024

I took this image over two nights. 100 180 second lights, 50 flats and 15 darks all with an old C8 and Celestron 6.3 Corrector. That's all the weather would allow. No clouds and fairly good seeing. I do very basic processing including Pixinsight's Gradient Corrector, Blur Exterminator, Noise Exterminator, Arcsinstretch, add in a Luminous layer, SCNR, Curves Transformation. Problem is I don't know whether this is as good as it gets because that's just the data from the scope or I'm terrible at processing and missing steps. The galaxy is soft. After looking at several NGC 4565 taken with similar SCTs, mine is sorely lacking in "sharpness." Comments and criticism PLEASE.

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Omiros Angelidis

Apr 7, 2024 · Edited: Apr 7, 2024

To start with in my eyes looks ok. What was the setting you had at BlurX for the sharpening of the non-stellar?

Did you pass each channel with localized histogram transformation at all?

Also the eccentricity of the stars look a bit off.

By far not a pro here but thought to throw this on the table!

cheers!

Sean Mc

Apr 7, 2024

How was the seeing on those nights. I have my edge hd set up right now, and it was clear last night, but the seeing was so bad i didn’t even image.

Apr 7, 2024 · Edited: Apr 7, 2024

Mike H - Sky View Observatory:
I took this image over two nights. 100 180 second lights, 50 flats and 15 darks all with an old C8 and Celestron 6.3 Corrector. That's all the weather would allow. No clouds and fairly good seeing. I do very basic processing including Pixinsight's Gradient Corrector, Blur Exterminator, Noise Exterminator, Arcsinstretch, add in a Luminous layer, SCNR, Curves Transformation. Problem is I don't know whether this is as good as it gets because that's just the data from the scope or I'm terrible at processing and missing steps. The galaxy is soft. After looking at several NGC 4565 taken with similar SCTs, mine is sorely lacking in "sharpness." Comments and criticism PLEASE.

Sir, that is... Extremely sharp for a C8- you're nearly matching my shot with IR Pass (below). Two ideas- I think processing is one reason you aren't getting much out of it, BlurX settings I use are .23 sharpen, -.23 halos, 1.0 nonstellar sharpen, Auto PSF. The other is probably the main problem, mirror flop/ focus shift. Standard XLT tubes don't have mirror locks that force the mirror to stay put while tracking over the night- this causes the focus to shift due to gravity as the mirror is shift-focused.

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Mau_Bard

Apr 7, 2024

Hi Mike, I share the same feeling when I look to my galaxies, therefore I empathize and appreciate your post, and I am extremely curious to read the feedback of the community.

I can give my 2 cents: recently with galaxies I tried to shorten the sub-exposure time, sometimes down to 120s-60s. I also am in the process to eliminate any anti pollution filter (I use OSC cameras), and this is IMO improving visibly the image crispness.

Looking at your picture, that is definitively a crop, therefore exposing the smallest details, I see the stars slightly ovalized. The recent BlurX (be sure you have the latest level of AI, makes a great difference) corrects very well this kind of defect. You might want to experiment on different parameters. One possibility is to run it as "correct only" to regularize the stars, and then run it again with different parameters for non-stellar, until you get the best galaxy crispness.
BlurX should be executed in linear state at the beginning of processing.

It would be as well interesting to understand if the ovalization is coming from guiding (most probable) or a tilt in the sensor (not likely on a long focal, but worth to check. ASTAP has a simple inspection utility for tilt).

As said, I am curious to read other comments to learn about galaxies.
Ciao,

Mau

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Marc Dickinson

Apr 7, 2024

Hi Mike, I sometimes use an old C8 as well, your image looks fine to me. In your gallery you show your C8 with a Starizona reducer, just curious, have you tried the Starizona reducer?

Mike H - Sky View Observatory

Topic starter

Apr 7, 2024 · Edited: Apr 7, 2024

Marc, I needed a shorter visual back to have enough focus. Somebody gave me a tip on an Amazon site with a 7mm long adapter that is threaded. When this comes I'll go back to try the Starizona piece. I believe this will give me a little more focus travel and reduce the tilt. I'm anxious to give the Starizona Corrector a chance.

Thank you guys for taking a few minutes to help a fellow astrophotographer

My expectations for this old scope are not high. I'm aware of the hazards of Mirror flop etc. Since the majority of this imaging train goes right on my refractor, i don't really have much invested. Just wanted to know if i could shoot galaxies with it. There will be a new Starizona or Celestron Corrector for sale soon.

I'll try the ideas of some new adjustments to BlurX. I do run it at an early linear stage of processing. I have never changed the settings from default.

Mike

Mike H - Sky View Observatory

Topic starter

Apr 7, 2024 · Edited: Apr 8, 2024

Reprocessed using the suggestions and a minimal crop for stacking artifacts. I am much happier with this version. In my mind it looks sharper...

Marc Dickinson

Apr 7, 2024 · Edited: Apr 7, 2024

I needed a shorter visual back to have enough focus.

I thought that was likely, I had the same problem. I think maybe you'll like the Starizona better for image sharpness. Perhaps a shorter visual back will work in your case. My C8 looks like yours but is a 75-76 vintage and it wouldn't obtain focus with the Starizona and I don't believe a shorter VB would have helped...it still wouldn't bring the Starizona in enough. But I was still able to make it work. On my scope there is a 4-40 screw on the focuser with washer that acts a stop so the mirror won't go out too far and off the internal baffle. But my baffle also has a split ring to prevent the mirror from sliding off (I don't think all C8s have this) so I just removed the screw and washer and it gave me 5 more turns. I only needed 2 for focus so it now works fine.

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Mike H - Sky View Observatory

Topic starter

Apr 7, 2024 · Edited: Apr 7, 2024

Very interesting Marc. I may look into this. Mine is an 1981. I believe it has good optics especially for the era. The mirrors and corrector plate are perfect. I could achieve focus but barely any infocus. Maybe a half turn or less. Autofocus definitely wouldn't work. The shorter piece will for sure help me.

Nice looking work area by the way

I'm surprised the ZWO bracket works on your scope. I was under the impression it wouldn't. I bought a 3D printed piece. I like yours better. More robust.

Mike

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Marc Dickinson

Apr 8, 2024

I'm surprised the ZWO bracket works on your scope. I was under the impression it wouldn't.

I may have modified bracket slightly, maybe different length screws,I can't recall, anyway it works fine . I only have one DSO image in my gallery with it. https://www.astrobin.com/lgk1ku/B/

Jeramie

Jul 25, 2024

I wanted to agree with what V.m said above. The image you have is good for a C8 and the Celestron corrector. I also agree with @Marc Dickinson regarding the Starizona reducer. I have the Starizona LF reducer/corrector on my C11 and it is a superior product to the Celestron in my experience.

Another thing I'd like to mention is your total integration time. 5 hours is ok if you're imaging with very fast optics, but I would not expect great results imaging at ~f/7 for that amount of time. If you get a chance, go and look at my Iris Nebula shots I did recently. One is at 2000mm (f/7, LF reducer) for ~17 hours (NGC7023 (Jeramie) - AstroBin), and the other at 540mm (f/1.9, Hyperstar) for 3 hours (NGC7032 - Hyperstar (Jeramie) - AstroBin). The amount of detail and sharpness you can create with a faster optical system over just 3 hours is nutty. My point here is that you need way more integration time with slower optics.

Great topic!

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Dave Rust

Jul 25, 2024 · Edited: Jul 25, 2024

I remember thinking something was wrong with my first reflector. I was used to 400mm refractor images and the new pics seemed so, well, soft. I continually checked colimation and focus. Slowly, over time, it became evident that 2350mm images from a reflector differ significantly from 400mm refractor images. Both the mirror technology and tremendous magnification render targets uniquely. My sharpening and processing steps evolved and I eventually produced pleasing, detailed images with the stronger scope. There was indeed a learning curve.

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