I’m back … Remember me, I’m that scary guy who loves the colour green in astro images – 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.
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
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.
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.
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 5.15° x 3.87°
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.
I’ve slept on what many of you said and I think I can see what you see on most counts, bar one. I still can’t perceive the “missing detail” 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. It’s 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 don’t like sharing my raw unprocessed data, but you are special, so I will share it with you.
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 & I’ll try to assist.
Cheers
Andy
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)
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
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.
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!
Some of you commented that my Eta Carina Nebula image was missing detail. Recall that sub-frames were recorded using a 55 mm f/3.6 optic at an image scale of 5.6" arc seconds per pixel. For completeness, I have appended a new version of the image enhanced with a mild application of the Local Histogram Equalisation (LHE) and Unsharp Mask filters. These filters emphasise more of the detail. The improvement in image quality is subtle and subjective.
One could probably reprocess the master lights using a work flow optimised to accentuate luminance detail. There would be a trade-off in some other aesthetic quality.
Still think your focus is off it still appears mushy. Love the colours however
Hi Nikolas. I think I will try from scratch again during the end-of-year break when I have spare time. Andy convinced me there is more detail contained in the master lights that I have not revealed.
