The Dark Shark and a RASA 11

[symmetal]

After all my troubles with the RASA 8 and dropping my RASA 11, I'm finally back in business. 😊 Had a few days of clear nights with no Moon a few weeeks ago so managed a few targets which I'm just now starting to process.

I also bought PixInsight a few months ago as I wanted to take advantage of BlurXterminator and with the help of Warren Keller's book and YouTube tutorials I've got it figured out to a useable degree. 😁

I also only discovered the Generalised Hyperbolic Stretch add-on a few days ago which makes stretching much more controlled, though you need to view the tutorial videos a few times to understand how it works. The 'Symmetry Point' control is very powerful in deciding where you want to apply the most stretching.

Also first time of using star removal which was great at reducing the rather flarey bright stars effects RASAs produce. Had trouble with it removing all the stars until I realised that StarXterminator works on a linear and not a stretched image like others do. This is useful as BlurXterminator and NoiseXterminator can be used fully on the starless image, and a modest BlurXterminator on the star image alone. I found NoiseXterminator produces significant star artifacts on a normal linear image with stars, which can be seen if you look at the before and after linear image, where a host of clipped coloured pixels appear where unclipped stars existed before. Running NoiseXterminator on the stars only extraction produces horrendous results as I suppose there is no real noise to analyse and it goes haywire.

Here's my first image of the Dark Shark Nebula which is composed of 2hr 44 mins of 2 min exposures with the RASA 11 and ASI2600MC in Bortle 3 skies. PS was used to blend the stars back in and clone/patch out any obvious residual star artifacts on the starless image.

I haven't posted the annotated image as it just found one entry of PGC67671 on the right.

Alan

[tooth_dr]

Very nice Alan. Really milky dust against a nicely controlled background 

[Sunshine]

Beautiful image!

[scotty38]

Great image, very well done!

[tomato]

A really distinct shark against the background, glad you are capturing images after all of your trials and tribulations.👍

[Fegato]

Nice one!  

I have a RASA 11 too and shoot in Bortle 3. I don't shoot longer exposures than 30 seconds, and that's still quite heavy on saturated pixels. You may find your stars are a little easier to control if you reduce your exposure time, and certainly easier to get some colour in to? However, difficult to stop the flaring artifacts given the wires across the corrector plate, however well you organise them, and however short the exposures.

Not sure what your StarXTerminator issue is, but FYI StarXTerminator is also designed to work with a stretched image. I use it 2 ways, linear and non-linear:

1. With a linear image, unscreen stars box unchecked, I will often remove stars in order to make DBE easier to apply (note - need to apply DBE with normalise checked). I then add back in straight away ($T+stars) before colour calibration etc. Adam Block has a youtube video showing how this can be really useful when starfield is quite heavy making DBE difficult.

2. After a light stretch (to whatever star intensity I think I'm after), I remove with unscreen stars box checked, and add back in right at the end of processing - iif((stars <=0.01), stars, 0.001); ~(~$T * ~stars).  

RC explains the unscreen issue here - https://pixinsight.com/forum/index.php?threads/unscreening-and-re-screening-recombining-stars-with-starless-images.18602/

 

[ollypenrice]

I think that's a very good rendition indeed. The little spiral has crisp detail, too.

Regarding when to use Star Xterminator, I use it on a partial stretch, say around 70% of final. I got a better result this way than with an application on the linear data.

Olly

[symmetal]

Thanks everyone for your kind comments. 🤗

I did initially do a partial stretch using Generalised Hyperbolic Stretch using  Mode 'Colour'  under 'Colour Options' which is similar to an arcsinh stretch where colour saturation is preserved, to where the stars were visible, and the background just visible, then ran StarXterminator and found around 20 stars were not being removed. I had brought the GHS Symmetry Point in a bit to reduce the degree of background stretch, and maybe that changed the star profiles a bit such that they weren't detected properly. I'll have to do another test to see if that was the case.

@Fegato Thanks for the tips. I'll give them a tryout along with the video. I'm new to PI so plenty to learn. 😀 I expose to swamp the read noise by at least a factor of 5 and with the ASI2600MC, for me that is around 50 seconds with the RASA 11, and I chose 2 mins to reduce the number of subs, and also increase the exposure time vs download time. The lack of star colour is also possibly due to BlurXterminator reducing star colour, when sharpen stars is selected. I'm just processing a new version of the Ursa Minor Dwarf and there is plenty of star colour all over the image with 2 mins exposure when I used BXT with sharpen stars at 0.0 which helped I think.

Alan

[tomato]

Apologies if this has been commented on before but does anyone else get the impression that with this dark nebula it is as if you are looking at a number of layers of the nebula slightly out of register with each other? Even the blue reflection nebula to the right of Bruce’s eye has a double vision appearance. 
I get this impression on all dark shark images, but it is quite striking on Alan’s image, with the darker background.

[symmetal]

2 hours ago, tomato said:

Apologies if this has been commented on before but does anyone else get the impression that with this dark nebula it is as if you are looking at a number of layers of the nebula slightly out of register with each other? Even the blue reflection nebula to the right of Bruce’s eye has a double vision appearance. 
I get this impression on all dark shark images, but it is quite striking on Alan’s image, with the darker background.

Now you mention it the top blue nebula does appear to have three similar structures one behind the other. The leading edge of the 'dorsal fin' also seems to consist of four very similar structures too. The denser patch on the front edge is repeated to a lesser degree in the structures behind. 🤔

Alan

[powerlord]

very nice - love it - and yeh I reckon it's a shoal of sharks one behind the other - if only we could fly 100 lights years or so to one side or the other, I'm sure we'd see them! 🙂