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Old 16-11-2019, 11:49 AM
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MLParkinson (Murray)
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Greatly Borgorised Eta Carina Nebula

Iím back Ö Remember me, Iím that scary guy who loves the colour green in astro images Ė some of you get really upset with my choice of colour palettes. My colour aesthetic is obviously deviant, but hopefully improving. Perhaps someone else in this forum is a weirdo and likes this rendition of the Great Eta Carina Nebula, my most recent attempt at portraying this spectacular object.

The most challenging aspect of imaging with a tiny f/3.6 astrograph is focussing the damn thing manually. The focus sweet spot is tiny for ultra-fast optics. It would be nice if someone manufactured a cheap universal electronic focusser, something I can afford to acquire using my modest salary.

3476 x 3476 pixel version: https://flic.kr/p/2hLfexf

Technical Details:

Borg 55 mm f/3.6 astrograph, Astrodon 3-nm SII, Ha, and OII filters, QSI 683wsg camera. Mount: EQ8. Two part mosaic imaged from suburban Sydney.

SII: 66x 14 minutes = 15 hours, H alpha: 115 x 14 minutes = 26 hours, OIII: 60 x 11 minutes = 11 hours.

Software: Nebulosity 4, PHD 2, PixInsight, Lightroom and Photoshop.
Attached Thumbnails
Click for full-size image (2019_05_15_Eta_Car_Borg_200mm_SIIHaOIII_Thumbnail.jpg)
191.5 KB61 views
Click for full-size image (Eta_Car_Borg_200mm_Ha_600s_1x1_131-220345.jpg)
189.6 KB36 views

Last edited by MLParkinson; 17-11-2019 at 10:46 AM. Reason: Adding an improved versions of thumbnail images to help the A team.
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Old 16-11-2019, 12:11 PM
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Hi Murray,

I can live with the bold psycho flouro treatment ok, but the what's happened to the details?
It's all gone kinda mushy - isthat the focus issue you're referring to?
Nice framing though
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Old 16-11-2019, 12:27 PM
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MLParkinson (Murray)
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Dear Andy, Your opinions are worth a lot, to me anyway - your photos are first class. Did you look at the version I uploaded to flickr? The compression on that version is not as severe. Try zooming in with the magnifying glass. Quiet a lot of detail was captured using the tiny little 200 mm lens.

https://flic.kr/p/2hLfexf
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Old 16-11-2019, 01:26 PM
Paulyman (Paul)
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Not sure what constitutes cheap, but according to Primalucelab their Sesto Senso fits the Borg 55.

https://www.primalucelab.com/astrono...f3-6-plus.html
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Old 16-11-2019, 01:30 PM
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I'm with Andy...the colours are ok and great framing!...but, hopefully you are ok with constructive feedback?..it appears you have smoothed out all the details (although it is a short FL I guess..?) and it looks like a water colour painting. It is clear there is plenty of data there but the processing is creating a paint by numbers look and the contrast is a bit too high.

Have another crack I recon

Mike
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Old 16-11-2019, 03:11 PM
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I agree with the others.


I like it a lot and the colour and framing are great however; too much ACDNR in PI perhaps and too much LHE?


But, hey, I'm no professional!
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Old 16-11-2019, 03:31 PM
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MLParkinson (Murray)
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No problem, all constructive comments welcome. Yes, I see, I think you are correct, the image has the look and feel of an oil painting, it is the way I have painted and mapped the colours. I did a lot of oil painting in my youth, old habits die hard. Or perhaps to me it looks perfect when it looks like a painting?

Where is all of the detail? Some detail disappears during noise reduction. I have another thought. The QSI683wsg camera has square pixels 5.4 micrometres. Here are the results using the BINTEL astronomy setup calculator:

Aperture 55 mm /2.19 inches
Maximum Magnification 111x
Resolving Limit (Dawes): 2.09" arc seconds
Ideal Resolution : 0.67" to 2" arc seconds
Resolution 5.57" arc seconds per pixel
Sampling Significant Under-sampling !!!!!!!!!
Camera Chip FOV 5.15į x 3.87į

I have been using drizzle integration to reconstruct some missing detail. However, to prevent under-sampling I should use a camera with square pixels <2 micrometres. Even better, I should buy a high-end Takahashi refractor with longer focal length and attach a large format camera with well-matched pixels. I would cover the same field and capture more detail.

Santa Clause, are you listening?
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Old 16-11-2019, 06:04 PM
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Quote:
Originally Posted by Bart View Post
too much ACDNR in PI perhaps and too much LHE?


Um what??????????
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Old 16-11-2019, 06:12 PM
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Hi Murray,
Can you please post a couple of your stretched Ha subs so we can see whatís going on in post?
Cheers
Andy
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Old 16-11-2019, 09:17 PM
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Quote:
Originally Posted by Nikolas View Post
Um what??????????

Adaptive Contrast Driven Noise Reduction and Local Histogram Equalisation in PixInsight.


ACDNR is used to reduce noise in the image and LHE is used to bring out the contrast in an image.


I have no idea if it was used, it was a guess.
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Old 17-11-2019, 11:11 AM
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Iíve slept on what many of you said and I think I can see what you see on most counts, bar one. I still canít perceive the ďmissing detailĒ issue. To my eye, the image abounds with detail. I will keep on trying to see what you see; it might take me months for my perception to change.

When saving the TIF file as JPG, the resulting image size is 7 MB for 95% compression. The image is very low noise; hence I infer that most of the 7 MB of data is detail in some sense.

Paul: Thanks for highlighting the Primalucelab electronic focusser. Itís a terrific suggestion. I will study it carefully. IMO, electronic focussing is essential for high quality astro work.

Bart: I did not use Adaptive Contrast Driven Noise Reduction (ACNR). From memory, I applied a single pass of the Local Histogram Equalisation algorithm; it is a powerful tool. I think I would have used a scale size of 512 pixels.

Andy: I have included a thumbnail of a single stretched raw H alpha sub, no calibration or processing whatsoever, exception for a single application of the PI screen transfer function. I donít like sharing my raw unprocessed data, but you are special, so I will share it with you.
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Old 17-11-2019, 04:52 PM
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Hi Murray,
Thanks for uploading that ha sub- hard to tell much though at that low res?
Maybe email it to me at high res - andy@andysastro.com & Iíll try to assist.
Cheers
Andy
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Old 17-11-2019, 10:10 PM
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The detail smoothing that some have alluded to is likely due to 2 factors:

1. the image scale of the captured image (some 5.6 arc seconds per pixel) which when uploaded was resized significantly from 3500 odd pixels to 730 pixels in the width (as I recall) dimension. That's a ~4.8x reduction. The final resulting image scale in the forum uploaded JPEG (~27 at seconds per pixel) is therefore somewhat coarse and that is what I think people are seeing as 'detail smoothing' and may be concerned with. That's not the case with the higher resolution Flickr image which shows plenty of fine detail and subtle nebulosity in the circumstances

2. The Rayleigh Resolution Limit Criterion for a 55mm objective is anywhere between 2.3 to 3 arcseconds for OIII and Ha wavlengths respectively and so the resolving capability is probably being limited by the optics somewhat as the seeing is likely/possibly better than that (2.3 to 3 arcseconds)

Best
JA

Last edited by JA; 18-11-2019 at 08:55 AM.
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Old 18-11-2019, 08:23 AM
AstroApprentice (Jason)
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Borg 55FL auto focus

Hi Murray,
Do you have the helical focuser for your 55FL? If so, Deep Sky Dad make a reasonably affordable motor/controller that can be adapted to the helical focuser of the RedCat, so I imagine it will work on the 55FL as well. If you feel you need to improve focusing then it may be worth contacting him about it:
https://deepskydad.com/autofocuser/redcat
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Old 18-11-2019, 07:16 PM
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Quote:
Originally Posted by AstroApprentice View Post
Hi Murray,
Do you have the helical focuser for your 55FL? If so, Deep Sky Dad make a reasonably affordable motor/controller that can be adapted to the helical focuser of the RedCat, so I imagine it will work on the 55FL as well. If you feel you need to improve focusing then it may be worth contacting him about it:
https://deepskydad.com/autofocuser/redcat
Thank you Jason, our hobby is expensive and saving money is always a big help. Yes I do use the helical focuser, and I was not aware of the "Deep Sky Dad" product range. I will study the options. Cheers.
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Old 19-11-2019, 03:52 PM
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Quote:
Originally Posted by MLParkinson View Post
Thank you Jason, our hobby is expensive and saving money is always a big help. Yes I do use the helical focuser, and I was not aware of the "Deep Sky Dad" product range. I will study the options. Cheers.
Hey Murray, again like 6188, I really like the high res image, looking at it from the point of view of what is dramatic and wow factor to my eyes.
Yes, the hobby is expensive, your images printed on canvas and sold at a local night markets should see an end to that dilemma.
Bravo!
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