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Xiga

California Nebula (NGC 1499) Bi-Colour - Nikon D5300a

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Hi guys

With the weather here in the UK being so bad recently, and with work commitments and other boring life stuff going on :tongue: I haven't done much imaging lately, but I did finally manage to get out and grab some OIII data a couple of weeks ago to go with my old Ha data of NGC 1499 from back in September. The Ha data was from first light for the newly modded D5300 and Baader Ha filter.

We have an outdoor sports facility only a couple of hundred yards from our house, and annoyingly the ridiculously bright floodlights don't turn off until after 10pm on weekdays, so even though there was no moon to contend with, I had no choice but to wait until the lights were off before I could start shooting the OIII. I thought about shooting more Ha while I waited, but in the end I decided to shoot some short subs without any filter, just to use for RGB stars. I stupidly didn't use my IDAS-D1 filter, and the scope ended up pointing almost directly at a streetlight for all the RGB subs. The result was a stack that had a simply insane gradient running through it, and which made gradient reduction on the stack impossible, as it was changing so much between subs. In the end I had to run gradient reduction on each individual RGB sub before stacking, and then run it again afterwards! Thankfully I only shot 20, so it wasn't too laborious. In the end I had something which, despite having a really ugly background, did at least have useable stars.

As for the OIII, boy was the signal weak with this one. I'm used to dealing with weak OIII signals on the D5300a, but this one really took the biscuit! Thankfully J-P Metsavainio's tone-mappng technique allows one to get the sledgehammer out for such cases, so I was able to stretch it far enough to get something out of it (even if it doesn't yield any fine structural detail for the OIII).

So this is 23 x 8 min Ha, and 9 x 20 min OIII subs. Calibrated with Flats and Bias, and dithered aggressively. The stars are made up of 20 x 90s subs. Everything shot at ISO 200.

The usual gear was used, HEQ5 Pro Mount, SW 80ED (with FF/FR), guided with PHD2 and a Finder-Guider and Legacy QHY5. Captured with SGP, pre-processed in APP, and processed in PS.

I have to say, I really like having the stars in a separate layer in PS. So much so, this is how I'm now going to process all my images from now on. It makes things so much easier being able to adjust whatever I want and not have to worry about constantly protecting the stars.

I'm not actually finished processing this one, but I thought I'd post it up for now anyway, and update it later. I still haven't ran any noise reduction on it yet, so I need to do that next, but hopefully the final version will not look much different to this. I did have some fun playing with the colour on this one. :icon_biggrin:

I have noticed today though, that it looks quite different on my work Dell monitor compared to my cheap Korean one from home. I think it looks a bit duller today, but I'm just not sure! What do you guys think, does it need more or less of something in particular? All comments welcome, I'm always looking to learn!

Cheers all!

 

California Nebula.jpg

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Worth waiting for.  Clear nights are few and far between!  Great job Ciaran.

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Hi Ciarán,

What an amazingly beautiful image this is, the colours really work and make the overall visual impact surreal! It's great that you dug deep and persisted with rescuing the RGB star data from the gradient monster, their tiny pin-point sharpness and their discernible colours are perfect and really complete the image, so much better than oversized bloated over-saturated stars. I'm no expert by any means, on the contrary,  but I find this image quite impressive!

Best regards,
Rudy

Edited by Rudy Pohl
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Thanks all! :smile:

I agree it's a bit surreal looking, psychedelic even, lol.

When i went searching for images of this target, i was expecting to mostly just see ones consisting of Reds and Pinks, but i was surprised to see all kinds of colourful renditions. Yellows, Oranges, Blues, Greens, Purples, the whole spectrum seems to get a look in depending on the imager and type of data captured, so i figured let's keep things interesting and not play it too safe :tongue2: 

I do quite like False Colour imaging i have to say. I know it's not everyone's cup of tea, but i like the freedom it provides. Trying to get the colours right on a Broadband image OTOH can be a right pain in the backside i find sometimes! 

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32 minutes ago, Xiga said:

Thanks all! :smile:

I agree it's a bit surreal looking, psychedelic even, lol.

When i went searching for images of this target, i was expecting to mostly just see ones consisting of Reds and Pinks, but i was surprised to see all kinds of colourful renditions. Yellows, Oranges, Blues, Greens, Purples, the whole spectrum seems to get a look in depending on the imager and type of data captured, so i figured let's keep things interesting and not play it too safe :tongue2: 

I do quite like False Colour imaging i have to say. I know it's not everyone's cup of tea, but i like the freedom it provides. Trying to get the colours right on a Broadband image OTOH can be a right pain in the backside i find sometimes! 

Ciaran, I feel you have a real firm grasp of processing and it’s always a joy to open your threads because I know it’ll be good! 

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12 hours ago, tooth_dr said:

Ciaran, I feel you have a real firm grasp of processing and it’s always a joy to open your threads because I know it’ll be good! 

You’re too kind Adam. :p
I probably spend on average about 10 hrs processing each image, making small changes one at a time. Then being extra careful not to butcher it at the end (which is so easily done!). I usually have to remind myself to keep the last few processing steps non-destructive, so I can go back and undo them if needs be. I do use Layer Masks but I’m also not averse to sometimes using Layers and a Low-Opacity Brush to just work on specific areas that I want to sharpen or whatnot. I think if a PixInsight user saw me process an image it would probably horrify them, lol.
 

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I thought the image was looking a bit flat, so I upped the contrast a bit. I think it gives it a bit more Pop and 3-dimensional appearance (you might need your sunglasses now though :tongue: )

I also evened out the background a tad, and applied some gentle noise reduction.

I might call this one the final version now. Unless anyone has any suggestions for possible improvements?

ps - Whilst I'm happy I was able to rescue the RGB stars, on close inspection there are actually quite a few that are yellow on one side and blue on the other (it's not a massive deal, you have to get pretty close to notice). Whilst some of this is no doubt down to the limitations of the 80ED's colour-correction abilities, I really didn't help myself by not using the IDAS-D1 LPF. The filter JTW Astronomy used to replace the stock D5300 filter with, has a bandpass of 300-700nm, so still allows more IR & UV light through than the IDAS-D1 would have done. When I inspected the stars in a raw RGB frame, the channels didn't quite line up, and from looking at other raw frames from the past in which I did use the D1, I could see that the channels were much better aligned. Also, i'm sure it didn't help that the target was very low on the horizon when I shot it. So lesson learned, always use the LPF when shooting RGB stars!

California Nebula v2.jpg

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Excellent image, love the color and detail... Definitely worth the battle you went through.

 

 

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Did you apply flats to the OIII data? I do wonder is some vignetting might have gotten through.

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1 hour ago, Adam J said:

Did you apply flats to the OIII data? I do wonder is some vignetting might have gotten through.

Hi Adam. Yes I always use flats and bias calibration files. Once calibrated, both that Ha and OIII looked nice and flat, with no visible vignetting. 

What is it you're seeing exactly? Is it the fact that the blue shows up in just the central area? I did stretch the OIII to a ridiculous level, and then brought the black point right in, deliberately clipping it even, which pretty much just left the central area of nebulosity. 

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      I thought i'd revisit this one, as i was never truly sure abut the processing originally. 
      So with this one, i sought to improve the stars (they're a big improvement) but also bring out more of the dark nebulosity. Did i go too far though?! Looking at it again today i think i may have. 🤔
      Details:
      Ha: 7 x 480s, 6 x 1200, 13 x 1200 (a little over 7 Hrs)
      OIII: 9 x 1200s (3 Hrs)
      RGB (with IDAS-D1 filter): 20 x 60s
      The usual Flats & Bias, stacked in APP and processed in PS. 
      Gear used: Nikon D5300 (modded); SW 80ED (522mm FL); HEQ5-Pro; SGPro and PHD2. 
      The original version can be seen on the Astrobin link.
      C&C welcome and clear skies folks!
      ps - At the moment this is still at 100%, but i'll probably end up down-sampling it to about 50%. I don't think it can hold up to 100% tbh. 
       
      Edit - Here's the new, now much more toned-down, version. It's a clear improvement, so i'll have to keep reminding myself not to try and go for big & bright, when subdued nearly always ends up looking better!

       
       
      Original, nasty over-bright version:
      https://astrob.in/346428/C/
       
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