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M31 under a bright moon

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#1 pyrasanth

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Posted 19 October 2019 - 06:48 AM

The moon continues to be bright. It rained for most of yesterday & the sky cleared for a couple of hours around midnight and stayer clear until 2.30 AM. The moon makes colour balance awkward so I kept the image dirty brown for now and as somebody pointed out its unconventional but I can correct when I have all the data.

 

I decided to have a go at imaging M31 as this would give me an idea of the field potential of the RASA. I was lucky as the sensor was aligned in the plane of M31 & its siblings.

 

The image below is a HDR composition- my first attempt in Pixinsight. 30 frames each on the QHY168C at 30, 60 & 120 seconds- so not a lot of integration time really- under 2 hours. I really can't wait for the moon to be out of the way to try more images as there is a bit too much noise so perhaps I need to double the number of frames and perhaps spend another couple of hours on the target.

 

As always let me know what you think.

 

Clear skies to you all.

 

HDR_RGB_TGV.jpg


Edited by pyrasanth, 19 October 2019 - 09:05 AM.

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#2 elmiko

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Posted 19 October 2019 - 07:28 AM

Looks great! It will look even better with the additional moonless data! Can't wait to see!


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#3 pyrasanth

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Posted 19 October 2019 - 08:05 AM

Looks great! It will look even better with the additional moonless data! Can't wait to see!

I seem to see a pattern and I don't know if its valid but when the moon is bright the sky is clear- it seems to happen time after time.

 

I had to sort a couple of issues this morning. The screws on the guide scope rings were loose- I'm lucky it guided so well last night- the guide scope could be rocked by hand!

 

I also added a UV/IR cut filter to Ultrastar camera on the guide scope as the stars looked really bloated- I bet this was the effects of the top & bottom of the visible spectrum which on a refractor and a mono camera will bloat the stars.

 

I love the RASA & QHY168 it produces some nice images and very quickly but not sure about the colour balance yet as red comes out a bit brown with the LPR filter but nothing that I can't get used to.


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#4 elmiko

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Posted 19 October 2019 - 08:14 AM

You're so right about the Moon! Seems to be cloudy on moonless nights!

I think you should do what you are doing. Seems to be working fine! You can take care of any red cast in Post processing.


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#5 pyrasanth

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Posted 19 October 2019 - 08:23 AM

You're so right about the Moon! Seems to be cloudy on moonless nights!

I think you should do what you are doing. Seems to be working fine! You can take care of any red cast in Post processing.

The image was stretched using the ArcSinH stretch in PI. This seems to work well on stronger data but you need to have clean data as the image comes out a bit dull afterwards so you need to lift the background which of course amplifies any noise. That's why the image posted is a bit dull because if I lift the background up comes the noise even with a previous TGV reduction which will only get better with more time which is relative because the image presented is only 1 3/4 hours. Imagine a full night with no moon- I think it will be pretty glorious!



#6 Astroman007

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Posted 19 October 2019 - 08:31 AM

It's rather brown. Don't get me wrong, I do like it...I just don't see very many images of the Great Galaxy that are so predominantly brown.

 

The Moonlight effecting the color balance?



#7 pyrasanth

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Posted 19 October 2019 - 09:02 AM

It's rather brown. Don't get me wrong, I do like it...I just don't see very many images of the Great Galaxy that are so predominantly brown.

 

The Moonlight effecting the color balance?

I think it is more down to 2 factors the moon & user error. The camera tends to move reds into dirty brown red if I'm not careful but to be honest I actually like the image & I don't see why everybody has to be conventional. I can look at the colour balance when I get new sets of data so I can produce a more conventional image. This is a work in progress (my excuse-lol). I altered the original post to reflect that the dirty brown colour is a work in progress.


Edited by pyrasanth, 19 October 2019 - 09:06 AM.

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#8 Johnathan Edwards

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Posted 19 October 2019 - 10:59 AM

I shall attempt to capture M31 tomorrow night with the 8" RASA and ZWO183MC Pro.  Any suggestions.  I own an L-Pro filter but was told not to use it for this target.



#9 pyrasanth

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Posted 19 October 2019 - 11:43 AM

I shall attempt to capture M31 tomorrow night with the 8" RASA and ZWO183MC Pro.  Any suggestions.  I own an L-Pro filter but was told not to use it for this target.

I'm not  sure that the inclusion of an LPR filter will be detrimental. I have the Celestron/Astrodon LPR filter and it gives me a beautifully flat field with very little gradient and that is really important for my light polluted sky. I just need to master the colour balance from the results and I think I will be very happy. Some LPR filters can significantly change colour rendition but as always its a personal decision to use or not.

 

M31 has significant dynamic range differences at the core & periphery. I suggest you use three sets of exposures try 30 seconds, 60 seconds & 120 seconds. Calibrate & register the frames as a complete set then integrate the sets by exposure length. This will give you three sets of integrated images. You can then use a HDR process to combine the three sets thus preserving the dynamic range. Notice on my image the core is not burnt out which would happen if you did not use a HDR type process (its one way to preserve the core but not the only way but its easy in PI).

 

Long exposures on your setup will not be necessary. I look forward to seeing your result. I suggest you aim for a minimum of 50 subs at each exposure level to fully deal with any noise. I did not dither as the 168C appears to have very little noise so I used the extra time to grab more frames. Focus is really critical so spend some time getting that right and refocus every 20-30 frames captured if the temperature is changing significantly- you may have temperature compensation set which makes that aspect easier.

 

I hope this helps & clear skies to you all.



#10 pyrasanth

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Posted 19 October 2019 - 02:37 PM

I looked at the colour balance of the image & by adding an L layer extracted from the OSC RGB we can begin to move the colour back in the right direction. Still needs more subs and a bit more work.

 

LRGB_HDR_RGB_TGV.jpg


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