[RCC] My very first DSO image, would love some feedback Requests for constructive critique · Daniel · ... · 10 · 599 · 0

starbuck3108 0.00
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Hello everyone, complete beginner here and new member of astrobin. I recently purchased my first scope and the other night finally had a break in cloudy weather to image the tarantula nebula. This is my first (proper) attempt at collecting data and processing in pixinsight. I would love some feedback on my end result.

https://www.astrobin.com/391506/?nc=user

The moon was quite bright this night unfortunately (77%) and this is in my light polluted backyard. 1.5 hours integration (27x150s unguided), 20 darks, 50 flats, 100 bias. Also FYI I shoot with an olympus m4/3 camera which is definitely not the best for low light (noisy sensor). My scope is a williams optics FD80 with 555mm focal length.

Workflow (pixinsight) -
sub frame selector
create master dark & bias
create master flat
calibrate lights and debayer
Align and register
colour correction using channel extraction and recombination,
automatic background extraction for left over gradients and background neutralisation
Multiscale linear transform for noise reduction
Non linear stretch
HDR multiscale transform and curves adjustment
star mask

Things I know I can improve on, firstly focus. I also am not sure how I went with colour calibration. A lot of images of 30 Doradus are in narrowband so it was hard for me find a good example to go off. I will also look to acquiring more subs to get a high total integration.

Thanks for any input!
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2ghouls 6.71
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Very good first proper attempt!!

The tracking looks to be excellent considering 150s subs and no guiding on an EQ5.

I think the color balance is pretty good, a bit too green/blue, and you have retained a lot of star color which is very impressive for a beginner.  To improve the color balance a tad, I would run SCNR on the green channel at about 40% intensity. It looks to me to be a tad too green, which might be hiding some of the natural magenta/red in the scene. Another possibility is your camera didn't capture the reds as well, in which case there are ways to boost them relative to the other colors in post-processing. Since I think your star color is already quite good, I would suggest making a fuzzy range mask and then subtracting your star mask from it using pixelmath (range_mask-star_mask) that should leave you with what I call a nebula mask. I would try then increasing brightness and saturation of the nebulae. To make the reds pop, you can apply ColorSaturation just to the reds with the mask applied. Yet one more thing to try for color balance if you start over: PhotometricColorCalibration (PCC) is pretty amazing. I always use a G2V star as the white reference.  I would suggest using DynamicBackground Extraction then ChanelExtraction/Recombination with LinearFit then PCC. After all that if it still looks too green, run SCNR at a low value.

By "star mask" I assume you mean you applied a star mask and then applied  MorphologicalTransformation to shrink the stars? This can work in moderation, but the star mask has to be quite good for it work well and not leave artifacts. It definitely helps the image when small, but if you blow it up to 100% it looks a bit odd to my eye- like the dim/smaller stars are too dim compared to the bright stars. However this could also be a focus issue which you mentioned you were still working on.  I would be curious to see what it looks like with no star reduction or at least less star reduction. For focus, I highly recommend a Bahtinov mask if you don't already use one.

Cheers, Nico
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starbuck3108 0.00
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Thanks Nico! Such great feedback. I actually forgot to run SCNR so I will definitely give that a shot. I will also have a go using pixel math. I haven't used that process yet but I am used to using something very similar in ArcGIS mapping software. I wasn't sure how to mask just the nebula so I will give that a shot as well! That sounds like it will really help the nebulosity which is definitely something that could be improved.

Yes you're correct I used morpological transform. To be honest I did it because I see a lot of others doing it but I am not convinced yet that I actually like the idea of it yet. I know some love it and some hate it. I saved my process at each step so I can go back and see what it looks like without the star reduction.

I use a bahtinov mask for focus. I think I was pretty close but I noticed that in live view with my cameras "live view boost" mode to help you see the screen in dark scenes it made the image a bit blurry/noisy and it jumped around a bit. I think if i take that off and focus on a nice bright star like Canopus I should be able to focus without live view boost. We shall see!

Thank you again for your feedback, very helpful 
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starbuck3108 0.00
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Oh I just realised that I follow you on youtube and your start to finish and equipment overview videos were two videos that I watched multiple times to figure out where to start. Thank you!
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iamsiggi 0.00
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I use with my Olympus cameras on DS most of the time 4 minutes exposure at ISO800 at F/4.
On F/2 photo lenses I can use 60sec ....
That give enough light to the often very weak objects.

Simply look at histogram of a frame - the Histogram peak (that represent the Background) should come 25-50% of the left corner.

Siegfried
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starbuck3108 0.00
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Wow Siegfried your photos are great! Inspirational to keep pushing on seeing what you can achieve with them
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iamsiggi 0.00
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Daniel:
... your photos are great! Inspirational to keep pushing on seeing what you can achieve with them


Thank you Daniel,
I hope you get some hints of the data description at the pictures.

PI is complex and I had good teachers here in Austria.

Siegfried
Edited ...
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roofkid 1.20
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Hi Daniel,

I think you did a good job for starters. I really like this area and you are one of the lucky people who has access to this part of the night sky
Since you ask for comments and critique here are some areas where I think you will get the most improvement.

Based on looking at the full resolution I would say the image is slightly out of focus. If your camera has live view capabilities I would recommend getting the brightest star in the night sky into the center of the sensor and focusing for the smallest appearance of that star with the highest (digital) magnification of your live view. Be aware that focus will change if there are large temperature differences (e.g. scope in 22°C car and outside temperature 0°C). Expect about 30m cooldown on a refractor.

Unfortunately improving the focus of the images will make guiding problems more apparent. It kind of depends on how you want to go about this hobby but there are a few options. I would recommend you getting an autoguider which means a small extra cheap scope and a small cheap camera which will watch the movement of a star and send corrections to your mount. If you do want to stay away from the computer part than I recommend getting a Lacerta M-Gen, it is a stand alone autoguider. The advantage of an autoguider is that you will get better star shapes and the images will be sharper in the end. Another important thing is dithering, moving your mount a small few pixels automatically which will be very helpful against fixed pattern noise.

Obviously post processing is an important part of this hobby and it really helps to learn much there. However what I notice in myself is, that I am getting more and more focused and use less and less processes. What I mean by that is that I mostly use a very basic workflow and try to improve the underlying data by capturing more for example. It's something I adapted from music post production. You cannot fix a bad recording even though ppl think you can. That's my motto. So my suggestion would be to use in order:
SubFrameSelector - I would discard all frames with bad FWHM, eccentricity or that have a lot less StarSupport value (means something like a thin cloud)
Stack everything
DynamicCrop - remove stacking artifacts
Automatic or DynamicBackgroundExtraction - remove gradients
PhotometricColorCalibration with BackgroundNeutralization enabled
Stretch the image
CurvesTransformation for contrast and saturation

If you have that down you should already have a very good base image.

Cheers,
Sven
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Starminer68 2.41
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Great start! And great target! I also started my hobby with Tarantula nebula 5 years ago https://www.astrobin.com/125619/?image_list_page=30&nc=&nce=
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