My version of Andromeda core dust lane detail

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Menno555
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My version of Andromeda core dust lane detail

Post by Menno555 » Fri Sep 04, 2020 7:08 am

Inspired by RonAM (viewtopic.php?f=16&t=3070), I too had a go at the M31 core.
After almost 5 weeks there was 1 (one!) clear night ... but of course it was the night with 100% full moon and seeing and a bit hazy ... so the quality is not that good, so I consider it a test. Also the first time I could do M31. Will do this again for sure on a good night but the next 4 weeks are again predicted with those fuzzy suckers :(
Had some fun to clear out the bright core in Photoshop. It really is to get the core and dust lane details, so it's over-processed on purpose :)

Bortle 8
Meade LX65 8" f/10 ACF OTA
Ioptron CEM25EC mount (no guiding)
Optolong L-Pro filter
Zwo ASI294MC Pro camera

Captured with SharpCap Pro @ -20 degrees Celsius / Gain 120 / Offset 4 / White balance R50/B50
80 x 30 seconds
22 x 120 seconds

Stacked in DeepSkyStacker 113 lights + 40 darks + 100 flats + 100 dark flats
80 lights + 30 darks + 100 flats + 100 darkflats / saved as FITS
22 lights + 20 darks + 100 flats + 100 darkflats / saved as FITS
Stacked the 2 FITS, saved as TIF.

Processed in Photoshop: Levels, Curves, Shadows/Highlights, color strengthening. Astronomy Tools actions: Contrast enhancement, noise reduction.

Full 3000px version here: https://i.imgur.com/uuCEv8H.jpg

Image

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oopfan
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Re: My version of Andromeda core dust lane detail

Post by oopfan » Sat Sep 05, 2020 5:38 am

Hi Menno,

Very delicate detail in the core, I like! I also like these mini-challenges we've got going among members. I'd like to add my own.

I wish I could say that I imaged this from my backyard but alas the weather continues to be terrible and furthermore there is no way on Earth that my lowly refractor could have captured this.

Last week I captured 12 subs of Edwin Hubble's famous variable star in M31. Two of those frames were suitable for photometry and the remaining 10 frames I pushed off to the side. The telescope was imaging at a relatively low elevation above the horizon of about 35 degrees. In my experience that is too low and it showed at a high zoom factor. The other day I got the wacky idea of taking all 12 frames and processing them as a regular AP image. In my first attempt I used the tools I had on hand: AstroImageJ and StarTools. Unfortunately my license for APP expired months ago since I mostly do photometry now. Post-processing doesn't interest me much so the results were only satisfactory. Dave (@turfpit) kindly offered to have a go with it using AstroPixelProcessor (APP). His results are as follows and stunning at that.

The very center of the galaxy is at the upper edge of my image, about 30% in from the right edge. Your image shows it at the center. The first dust lane you can see just below the galactic center is the primary dust lane in your image. My image loses a lot of detail in it because we stretched our image much farther. The second, wider dust lane in my image just about registers in your image. That second dust lane contains a lot of HII regions that will look quite stunning in hydrogen-alpha.

The tech specs:

12x300s luminance
RCOS 12.5" F/9 Ritchey Chrétien
10 Micron GM2000 mount
FLI ML-11002 Class1 Mono CCD 2x2 Binned
KAI-11002 36x24mm sensor, 9 micron pixels

Notes:

Over the years there has been a raging debate on the forum over long exposure vs short exposure. I've advocated for long exposures but I've moderated my position since developing a calculator that solves the CCD equation. Exposure is primarily a function of Read Noise. High Read Noise cameras, like this one at 13 electrons, require a longer exposure in order to acquire a good signal-to-noise ratio (SNR) on a single frame. Contrast that with low Read Noise CMOS cameras which most of you have, the exposure length can be much shorter in order to achieve a good SNR. There is no harm in taking longer exposures with CMOS cameras but you run the risk of unsightly star saturation.

Brian

Here it is:
M31-1_filtered.jpg
M31-1_filtered.jpg (347.21 KiB) Viewed 540 times

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Menno555
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Re: My version of Andromeda core dust lane detail

Post by Menno555 » Sun Sep 06, 2020 6:59 am

Thanks Brian!
Well, you just made me add another note on my To Do list: M31 in RGB + Narrow :)
I myself don't have real experience with longer exposures. Partly because I don't use guiding, partly because I'm in Bortle 8. Did read about it though and sometimes it indeed seems like the same "battle" between refractor and reflector users :) But for me the "more shorter exposures" works fine.
And yes, those challenges can be cool. Personally I like the challenges where you think "I can never do that with my setup" and then try, so it is a *real* challenge.

Menno

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Re: My version of Andromeda core dust lane detail

Post by oopfan » Sun Sep 06, 2020 3:51 pm

Hi Menno,

I can't remember if we had this conversation before but I've analyzed your telescope and camera combination. I can't find any reference to the bin mode you are using so I assume it is bin1. If that is the case then you are way over-sampling which simply means that you are spreading the photons of your object over too many pixels. The result is that your images are dimmer than they need to be. If SharpCap offers you the ability to raise it to bin 2 then your images will be noticeably brighter. It is worth a try.

I inputted your telescope and camera characteristics into my website. I noticed right away that your Resolution (column #3) is beyond what you can achieve from home at your Bortle 8 site. You can only achieve that in the Swiss Alps or Kitt Peak National Observatory, Arizona, USA. It's just not possible from where you are. In reality your atmosphere is probably scrambling light over 3 arc-seconds so you are needlessly diminishing the brightness of your images for no net benefit.

At a minimum I recommend doing all imaging at bin 2. Also, experiment with bin 3 if it is available. At bin 3 your telescope/camera is competitive with the scopes at the remote site that I pay to use.

Think of it this way. If you are spending 120 seconds to capture a frame at bin 1 then you can get the same result in 30 seconds at bin 2. Furthermore, if your mount is capable of tracking for 120 seconds, just think of how much brighter your images will be using bin 2.

Brian

PS: This is not crazy talk. Half of the scopes at the remote host use bin 2 mode. It's because the camera's pixel size is too small for the focal length of the telescope. Instead of going through the hassle of selling the camera and buying a new one with larger pixels, simply switch to bin 2. It is a very common practice.
Menno Pier Analysis.jpg
Menno Pier Analysis.jpg (118.77 KiB) Viewed 493 times
Last edited by oopfan on Sun Sep 06, 2020 9:39 pm, edited 1 time in total.

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Re: My version of Andromeda core dust lane detail

Post by Menno555 » Sun Sep 06, 2020 8:54 pm

Brian, thanks for all the interesting info!
My setup as it is, indeed gives oversampling but I knew this when I bought the 294 camera. For sure I will try what binning 2 brings! And if I remember correctly there is also 3. Will experiment with it.
Btw is using an ROI giving the same result?
And another question: the fifth kolom says Faint DSO. How low is Faint in magnitude?

Menno

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Re: My version of Andromeda core dust lane detail

Post by oopfan » Sun Sep 06, 2020 9:14 pm

Menno,

To answer your question I need to explain that this website I designed helps me take better images at the remote host. The "G300s SNR" column is a comprehensive measure that uses a dozen properties of the telescope and camera (i.e. Pier). It asks the question "If I point my scope at the zenith at a Bortle 2 site and take a 300s exposure what would be the signal-to-noise ratio (SNR) of a single sub of deep space?" The higher the number the more light-gathering power at the sensor. So you see I've included three variations of your scope in the list. This is how your scope would perform using that criteria.

Now to answer your question of Bright DSO vs Faint DSO. The mean SNR value of all of the Piers in the list is calculated. If any given Pier has an SNR value greater than the mean then it is said to be good for Faint DSO. So you can see that if you were to run your camera at Bin 3 under these conditions then it would fall into this category.

My suggestion is for you to try Bin 2 and see what you think. Frankly I don't know how this affects the Brain if you use it. That would be a question for Robin.

Brian

PS: Don't worry about the use of Bortle 2 in the calculations. I could have used Bortle 8 but it would not affect the rankings. It would just lower the SNR values for all Piers but the rankings would stay the same.

PPS: Yes, ROI will give the same results.

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Re: My version of Andromeda core dust lane detail

Post by oopfan » Sun Sep 06, 2020 9:46 pm

Menno,

I made an honest mistake when I said:

"Think of it this way. If you are spending 120 seconds to capture a frame at bin 1 then you can get the same result in 60 seconds at bin 2. Furthermore, if your mount is capable of tracking for 120 seconds, just think of how much brighter your images will be using bin 2."

change the "60" to a "30", like this:

"Think of it this way. If you are spending 120 seconds to capture a frame at bin 1 then you can get the same result in 30 seconds at bin 2. Furthermore, if your mount is capable of tracking for 120 seconds, just think of how much brighter your images will be using bin 2."

Explanation: In bin2 mode the signal from each 2x2 matrix of pixels are combined into one pixel. So for example if you have 100 electrons in each of those four pixels then you will have 400 electrons in the resulting pixel.

I've edited my post to reflect this.

Brian

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Re: My version of Andromeda core dust lane detail

Post by Menno555 » Sun Sep 06, 2020 10:18 pm

Again thanks Brian :)
I will check with the brain too with bin 2. For now the brain always gives the same values: gain 120, brightness/offset 4 and always very short exposures like 30 seconds.
And yes, I see that difference what you mean with 120 to 30 seconds. It's again that magic number 4 :)
Oh, and what is a pier?

Menno

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Re: My version of Andromeda core dust lane detail

Post by oopfan » Sun Sep 06, 2020 11:51 pm

Menno,

To answer your question "What is a Pier?" I'd like to start with four main categories that go into the calculation of SNR:
1. Telescope (i.e. aperture, focal length, diameter of secondary mirror if applicable, etc.)
2. Camera (i.e. pixel size, bin mode, read noise, dark current, etc.)
3. Observatory (i.e. sky brightness aka Bortle class)
4. Target (i.e. surface brightness of the DSO, for example M81 is 21.7 magnitudes per arc-second squared)

A Pier combines Telescope, Camera, and Observatory.

For the purpose of the Pier Analysis the computer code overrides the Observatory of each Pier so that it only considers the Telescope and Camera. Then it says that all telescopes and cameras are under the same Bortle 2 skies in the hills of southern Spain.

One thing we haven't talked about is something called a Project. When you create a Project you tell it the Pier and the Target. So for example if we have a target called "M81", then we can create a project by selecting "M81" and "Menno Bin 2". The default project name is "M81 at Menno Bin 2". While editing the Project you can select the exposure and frame count. The program will automatically calculate the SNR Per Sub, SNR Per Stack, and Total Integration Time. Projects use the Observatory information when the Pier was created, so since "Menno Bin 2" is located somewhere on Earth with Bortle 8 skies then the calculator will use Bortle 8 when calculating SNR.

When planning my projects I adjust the frame counts to achieve a minimum total SNR of 30. I discovered that this is what puts you in contention for "Image of the Day" honors. SNR 30 is much easier to achieve under Bortle 2 skies than Bortle 8.

If I could I would give you access to the website but it is still a work in progress.

Brian

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Re: My version of Andromeda core dust lane detail

Post by Menno555 » Mon Sep 07, 2020 8:58 am

Brian

Thanks for the explanation.
I'll keep that offer for acces to your site in mind. I know myself: all kind of new things, my brain gets triggered and wants to understand it all and next thing you know, I have a 1000 questions and that is then in the way of capturing ;)
For now I'll keep on working on instinct, mixed a bit with the things I learn here and from other sources. Like with this M31 capture: my goal was to have a capture of the core without it being overblown with light. So just a bit of my own experimenting, bit of info learned here, using the Smart Histogram Brain and then mix those results.
And although I have a bit of theoretical understanding on SNR now, I still don't how to apply that in real life. But that doesn't matter for now, I'm very much a hands on guy and I am very happily busy, tweaking and experimenting ... if there are no clouds :| And maybe I'll have an "Image of the day" capture in a few years (although that's not important for me :) )

Menno

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