NGC6995

[Vox45]

Here's my 3rd attempt at a DSO. After M31 and M101 I tried to capture a nebula... I am still struggling with colors. I saw many different examples (red hue, extreme saturation,etc) I never quite know what it "should" look like... I lack experience and still have a lot to learn. All comments are welcome.

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Imaging telescope or lens: Sky-Watcher ED 80 Pro APO / Imaging camera: Canon 1000D (modded) Canon 1000D / Mount: Orion Sirius EQ-G /Guiding telescope or lens: Orion Mini 50mm Guide Scope

Guiding camera: ZWO ASI 185MC

Focal reducer: Skywatcher .85x Focal Reducer & Corrector

Software: INDI/Ekos

Dates: Aug. 5, 2017

Frames: 39x300"

Integration: 3.2 hours

Locations: Observatoire AstroQueyras, St-Veran, Hautes-Alpes, France

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[ollypenrice]

Most images in RGB give a red/blue colouration similar to what you have here, though your red is somewhat more yellow-orange than most. This particular red tone is also visible in your red stars so it probably could do with a small tweak to bring it in line with the stellar astro-physics. This is always a good check on your colour balance. Many planetaria will give you the colour B-V (blue minus visible) index of the stars which you can check against internet souces like this one: http://curious.astro.cornell.edu/physics/78-the-universe/stars-and-star-clusters/general-questions/372-how-does-the-color-index-of-a-star-relate-to-its-actual-color-intermediate

Or there's this visual equivalent.

Your reddest stars strike me as being equivalent to B-V 1 (ish) which probably isn't red enough? Note that, at the blue-violet end, these sources seem to disagree somewhat but there are very hot stars whose peak emission falls outside the visible spectrum.

Olly

[Vox45]

Thank you Olly for the analysis, I appreciate !

I will look into this. I still have A LOT to learn.... and the perfect weather to do so right now

 

[gnomus]

Hi Vox

It is recognizably the Eastern Veil so that's a great start.  You talk about comparing your image with the colours you have seen in other images of this object.  However, many of the images of this are taken through NB filters (especially Ha and OIII) and combined in such a way that they inevitably give a bold, saturated result.  I wouldn't try to chase this same effect with a DSLR.  A good tip is to concentrate on getting nice stars and star colours, and let the nebulae fall where they may.  As Richard Wagner once said, "Deutlichkeit ['clarity'] - take care of the little notes and the big notes will take care of themselves".  On the other hand, what did he know about astrophotography?  

It is a little difficult to say from the size of image you posted, but I wonder if you could pay a little more attention to focus.  When I started out in AP, I hadn't really appreciated the challenge of: 1) achieving good focus in the first place; and, 2) how much focus might change as the night wore on and cooled (especially that first couple of hours)...  I mean infinity is infinity, right?   

Thankfully someone (probably a fella called Bahtinov) came up with the Bahtinov mask.  At first, I couldn't get this simple device to work, until I realised that I needed a reasonably bright star to be in the FOV.  And I told myself that I didn't need to stop imaging, slew to a bright-ish star and check focus with the Bahtinov.....  The good news is that the Bahtinov mask will probabaly be one of the cheapest astrophotography gadgets you will buy -  https://www.firstlightoptics.com/bahtinov-focus-masks/starsharp-bahtinov-focus-masks.html  

Good luck

[Vox45]

"A good tip is to concentrate on getting nice stars and star colours, and let the nebulae fall where they may.  As Richard Wagner once said, "Deutlichkeit ['clarity'] - take care of the little notes and the big notes will take care of themselves".  On the other hand, what did he know about astrophotography?  "

This is a good tip that I will try to apply I never thought of it that way. I do see some picture sometimes that have a really good looking nebula but in the background the stars have all sort of weird colors. So I will keep that in mind!

"but I wonder if you could pay a little more attention to focus"

Believe it or not I have a Bahtinov mask ! (I am always amazed by the simplicity and genius of the device) but I did not refocus during the night, only at the beginning of the session. Big mistake. I tried to keep the light frames that looked the best but lost a lot due to poor focus.

My PA was not perfect, I have a slight field rotation. I realised that when I added all the image together, I had to crop the final result.

So, next time:

- Perfect PA

- attention to focus and refocus during the night

I could not use my dark frames as they introduce strange artefacts. I will need to understand why. Dark frames are easy to take so I do not understand what happened there.

With your tips and Olly's pointer on the color index issue, I'll try to give another go at reprocessing but if my raw data is garbage then I'll have to capture some more light frames... garbage in, garbage out as they say

Anyways thanks to you both for taking the time to look at this !

[ollypenrice]

You might try using a master bias as a dark rather than a 'proper' dark. If you can combine this with a large scale dither (12 pixels or so) you'll be following the advice of Tony Hallas whose DSLR images are good.

Olly

[Vox45]

I followed a different tutorial and was able to use the darks without that strange artifact. In my opinion it looks much cleaner and the stars are sharper now. I also reprocessed to get more colors in the stars and changing the contrast made the faint stars less visible, leaving a image easier to read...

I still feel that the background sky is a bit reddish though...

 

Original for comparison

[gnomus]

Colour balance is more pleasing in V2 and the background is much better - to these eyes, anyway.

[ollypenrice]

The nebular colours are better to my eye but the background looks red. Simply bringing in the black point in the red channel might hit the spot.

Olly

[gnomus]

Now that I see it on my big monitor (rather than iPad) then I can see that Olly is right.  In Photoshop a randomly chosen bit of your background reads: R22: G12: B12.  

[ollypenrice]

This might be the moment to confess that I have never done very well in following R Jay GaBany's piece in Lessons From The Masters regarding the shaping, in curves, of the individual colour channels. However, Vox's second image suggests that a custom red curve might be in order here. Maybe bring in the black point in red and then hold down the lower part of the curve while lifting the upper part. I'm guessing.

Olly

[Vox45]

Thanks for your comments ! I agree that there is something wrong with the "red" background... I am now starting the chapter "curve transformation" of the excellent book "Inside Pixinsight" by Warren A. Keller and hopefully I will be able to better understand how to correct this

I am amazed at the different results I get using the same set of data. I now understand how important the pre-processing and post-processing work is. I will revisit my old data (M31,M45) and reprocess them with my new found knowledge

The learning curve is really steep but I am having a lot of fun!

[tooth_dr]

28 minutes ago, Vox45 said:

Thanks for your comments ! I agree that there is something wrong with the "red" background... I am now starting the chapter "curve transformation" of the excellent book "Inside Pixinsight" by Warren A. Keller and hopefully I will be able to better understand how to correct this

I am amazed at the different results I get using the same set of data. I now understand how important the pre-processing and post-processing work is. I will revisit my old data (M31,M45) and reprocess them with my new found knowledge

The learning curve is really steep but I am having a lot of fun!

I agree with getting different results from different processing.  I feel so far outside of the processing loop, that I'm at that point of maybe just not starting at all...