M101 in HaRGB

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Menno555
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M101 in HaRGB

#1

Post by Menno555 »

I wanted to add at least twice at much data but the clouds here of the last weeks (and coming weeks) are restricting me to the 7:20 hours I have now of M101.
It to low now here above the city and in a light polluted spot. So all saved and continue in around a year to capture more data :)

But for now I have this and I am really content with it. This object would really come forward in darker skies, so for my Bortle 7 this is not bad at all I think. But to get this, longer exposure times of 300 and 600 seconds were needed. I tried shorter but that just wouldn't work.

First time also that I used Ha data in a different way for me. Normally I would blend Ha and RGB in Photoshop. This time I isolated the red channels of RGB and Ha, did blend those together and then pasted that blend back into the red channel of RGB. Way more detail now and less noise too in comparison to the previous methode.
Noise is still there but that will be better with more data.

Bortle 7/6
Meade LX200 8" f/10 ACF OTA
Ioptron CEM25EC mount (no guiding)
Baader Neodymium Skyglow filter
Optolong L-eXtreme filter
Zwo ASI071MC Pro camera

Captured with SharpCap Pro @ -10 degrees Celsius / White balance R50 B50
Neodymium Skyglow filter: 40 x 300 sec / Gain 90 / Offset 4
L-eXtreme filter: 24 x 600 sec / Gain 200 / Offset 10

Stacked with DeepSkyStacker
RGB + Ha stacked separately

Processed with Siril and Photoshop
Siril: for both stacks Background Extraction and Histogram
Photoshop: blended the red channels of Ha and RGB and then pasted that into the RGB red channel. Curves, Levels, Astronomy Tools actions (Local Contrast Enhancement), Camera Raw Filter (blacks, color saturation, clarity, noise reduction), reduced to 2000px
M101 in HaRGB
M101 in HaRGB
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admin
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Re: M101 in HaRGB

#2

Post by admin »

Hi Menno,

another great image - I am always impressed by the amount of detail you manage to pull out from amongst really bad light pollution!

cheers,

Robin
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Menno555
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Re: M101 in HaRGB

#3

Post by Menno555 »

Thanks Robin :)

Yes, I've been told that a few times now. Someone (not here on this forum) even did accuse me of making up things, that with my unguided captures and Bortle zone, I never ever could have captures like this.
But for these detailed captures, longer exposure times are key. I could get nice results with for example 200 x 120 seconds but that gives less detail and more noise cause of the higher gain. I did test that and with objects like this here in the city, it works for me like that. Plus using low offset/brightness values for broadband.

Not guiding also helps. I use only tracking with that excellent Ioptron mount and that is one continues, fluid motion. While with guiding (correct me if I'm wrong) there are pulses.

And what also helps: I live on the 3rd floor (4th floor for the Americans :) ) and all the street lighting is below me. So I do not have weird bounces from things around me.
And I suspect that the Bortle map is not correct: it says Bortle 8 for where I live but I scaled that down myself to 7 before midnight and 6 after midnight.

Menno
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Re: M101 in HaRGB

#4

Post by admin »

Hi,

yes, total exposure time is the key, although you would get more faint stuff for the same 6 or 8 hours of exposure at a darker site of course.

If you measure your sky brightness using the smart histogram brain and get an e/pix/s figure, you should then be able to tinker a bit on https://tools.sharpcap.co.uk/ to see what Bortle number gives roughly your measured e/pix/s figure when you have selected the f-ratio etc of your equipment. Certainly being above the streetlights must help, especially if much of the lighting is relatively well controlled to point downward.

cheers,

Robin
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Menno555
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Re: M101 in HaRGB

#5

Post by Menno555 »

Ah, good tip Robin!
Are the results of the smart histogram somewhere saved in the log files? I don't have to wait then for a week or 2 until the clouds are gone here :P

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Re: M101 in HaRGB

#6

Post by admin »

Hi Menno,

yes, look for 'Sky background measurement complete :' in the logs - the value following will be the e/pix/s measurement (note: this is for 4.0 - unsure if it was logged in 3.2, but worth looking even if your logs are 3.2).

cheers,

Robin
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Menno555
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Re: M101 in HaRGB

#7

Post by Menno555 »

Found it, Robin. Thanks :)
Was a bit of a search cause that measurement is influenced by the filter. Found one of 0.45 e/pix/s which would mean Bortle 5.
But finally found a log with IR/UV cut filter and that gave 1.30 e/pix/s and that translates roughly into Bortle 6. For the zenith that is, I'm always pointing rather straight upwards.
So my own guess of Bortle 6/7 is a keeper then :)

Menno
timh
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Re: M101 in HaRGB

#8

Post by timh »

Hi Menno,

That is an extraordinarily good image. A lot of drama and contrast right down to the core but without loss of definition or making the stars too bright. As an experiment I tried decreasing the gamma and changing down the tone of my effort to see if I could achieve something similar to yours -- i.e. sacrificing detection of the extent of the galaxy for better definition. I was just interested to see how much of the difference in the two images was down to processing/ interpretation and how much down to the difference in the original image data (~ 3h at F5 v 9h at F10 --different Bortles etc.)

Suffice it to say that I got something similar but not quite as good -- my effort to produce fakes of the works of the Dutch masters fell short :-)

TimH
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Re: M101 in HaRGB

#9

Post by Menno555 »

Thanks so much Tim!! :D
I'm not sure myself how I come to this. I do know that I'm always rather low with gain and offset in broadband with the bigger objects. This indeed to give the brighter parts less "attention". Plus integration time. And like usual, a lot of gut feeling ;)
And with processing there are 3 things that make it all "pop out" more: after SiriL, in Photoshop the Camera RAW filter really does a lot.
Especially the Clarity, which really brings forward the bright(er) details without blowing up things. Downside of this, is that is also enhances the noise. Also, an overal Contrast reducement. This sounds counter-intuitive but i did find that if that is done in moderation, it brings forward the more fainter details.
And then the Astronomy Tools action set (from ProDigital Software). It has an action called Local Contrast Enhancement which does just that: locally increasing the contrast, so not blowing bright things up.
As an example this quick processing of M51. On the left the "normal" processing and on the right the same but with the 3 steps mentioned above applied. It's a bit overdone but is shows the impact of these 3 steps.

Menno
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timh
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Re: M101 in HaRGB

#10

Post by timh »

Thanks Menno,

Yes that is quite a striking demo.I see what you mean.

Your comments on processing were useful and although I don't have the same tool set (especially not a tool that would enhance contrast locally) it did encourage me to have a more serious look at what I am doing. In theory - I had collected significantly more light(because of the low F number and lack of a filter) from much darker skies using a telescope of the same aperture - and yet I would judge that you had produced the more attractive image.

So - using Affinity and PI 'curves' - I improved contrast and reduced star size/ brightness plus increased 'clarity' and then using a freeware version of a program called Photoscape X (only 16 bit) I found a tool to 'darken highlights' which seemed really useful for flattening out the image and improving contrast at the core. I am quite pleased with it now because there is now good detail (despite the poor seeing during some of the capture) and colour plus better contrast. So this is where I got to ..for now. the real problem with processing though is that the it is an endless path and difficult to know when to stop---and what is worse -- what looks pleasing one day may not the next :-)

Tim
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