M31

[Misange]

Hi,

I am very new to astrophotography (and enthousiast !) and I tried imagining M31 yesterday. Altogether this is also my first try with startools, (highly recommended by my son).
I processed my images in different ways : either stacking in DSS + startools or stacking in sequator and image processing in lightroom. The second method shows that M31 is there and stars are quite round and if I have some noise and the image is not perfect at all, the exposure seems correct.
I stacked 80 images (nikon D5600, 300mm f6.5, 1600 iso, 15sec x80).
I followed the recommandations for stacking in DSS about colors and other parameters. When I open the fts image, it is almost completely black, EVEN AFTER autodev ! I have to use the development module and push the digital development to see a (very red!) image with a faint galaxy. After wiping, M31 is there but huge artifacts on the corners (hu, more than corners at that stage !), artifacts that I cannot find when I develop the fts image on DSS or in sequator+lightroom.
What I am doing wrong ? What would you recommend ?
To check a local problem (behind the computer...) I downloaded the beautiful m31 fts from Gaetano to test. It opens very black but M31 clearly appears immediately on a high background when hitting autodev.

Thanks for your advice

[admin]

Hi,

I am very new to astrophotography (and enthousiast !) and I tried imagining M31 yesterday. Altogether this is also my first try with startools, (highly recommended by my son).
I processed my images in different ways : either stacking in DSS + startools or stacking in sequator and image processing in lightroom. The second method shows that M31 is there and stars are quite round and if I have some noise and the image is not perfect at all, the exposure seems correct.
I stacked 80 images (nikon D5600, 300mm f6.5, 1600 iso, 15sec x80).
I followed the recommandations for stacking in DSS about colors and other parameters. When I open the fts image, it is almost completely black, EVEN AFTER autodev ! I have to use the development module and push the digital development to see a (very red!) image with a faint galaxy. After wiping, M31 is there but huge artifacts on the corners (hu, more than corners at that stage !), artifacts that I cannot find when I develop the fts image on DSS or in sequator+lightroom.
What I am doing wrong ? What would you recommend ?
To check a local problem (behind the computer...) I downloaded the beautiful m31 fts from Gaetano to test. It opens very black but M31 clearly appears immediately on a high background when hitting autodev.

Thanks for your advice

Hi and welcome to the hobby!
This video may help.
You will want to Crop stacking artefacts away first before running Wipe. Wipe is easily confused by dark things that are not real detail. It will not work properly with these "dark anomalies" present in your image.
Also see here on how to prepare your dataset before using Wipe.
If you get really stuck, then just like Gaetano, feel free to share your dataset with us and we can take a look.
Hope this helps!

[Misange]

Hi Ivo
Thanks for the prompt reply.
I already went throufg the video but it does not help : my image is almost black after the very first autodev which I did not expect.
I guess that when I perform a manual devlopment, pushing the digital development to 80%, I increase the signal and all the noise with it...
I will go in detail through the suggested ling and will come back I I still cannot improve the results. Thanks for the help.

[admin]

Hi Ivo
Thanks for the prompt reply.
I already went throufg the video but it does not help : my image is almost black after the very first autodev which I did not expect.
I guess that when I perform a manual devlopment, pushing the digital development to 80%, I increase the signal and all the noise with it...
I will go in detail through the suggested ling and will come back I I still cannot improve the results. Thanks for the help.

Do let us know if you'd like us to have a look at the dataset.
(I have also moved this thread to its own topic)

[Misange]

I am still struggling to get somethng correct and I just dont know if this is because my initial file is poor or because I am new to startools.
Here is the link to the fts file
https://www.dropbox.com/preview/Photos/ ... e=personal
Thanks for your help !

[admin]

I am still struggling to get somethng correct and I just dont know if this is because my initial file is poor or because I am new to startools.
Here is the link to the fts file
https://www.dropbox.com/preview/Photos/ ... e=personal
Thanks for your help !

No problem!
I don't think you shared the link correctly though...

[Misange]

Argh... apparently my link is not public. I need an email address to send it via wetransfer or give access to my dropbox (I could not reactivate the public folder, in dropbox it seeems that a pro account is needed for that). Can you help with this issue ?

[Misange]

new try, through google drive
https://drive.google.com/file/d/1mQxdyq ... sp=sharing
or through we transfer (7 days)
https://wetransfer.com/downloads/e7f5c7 ... 954/8ec60d

[admin]

Thanks for uploading!

I'm afraid the dataset has very little signal; the light pollution is extreme, but the biggest problem, it seems, is that it was not calibrated with flats (or they were not succesfully applied?). There are some extreme gradients going on and lighting is very uneven. There are quite a few dust specks visible. Flats are not really optional I'm afraid and you will need them to solve these issues.

15 seconds exposures are very short and not really long enough to gather enough signal. Do you live in a very light polluted area? A light pollution filter may help and may allow you to take longer exposures.

The artifacts in the corners when using Wipe are indeed caused by thin stacking artefacts around the edges. Simply cropping these away helps.

Unfortunately, it's just extremely hard to get to the real celestial signal. The best I was able to do was this;

190825-andromede(1).jpg (119.79 KiB) Viewed 7421 times

The problem is that telling you how I did that will not teach you much about StarTools. Right now most of the processing flow is about working around the problems in your data, and that's not really what post-processing is about. I highly recommend you try to work on your data acquisition skills first. This will be needed regardless of what software you wish to use.

See what you can produce with longer exposures and flats.

[Misange]

Thank you Ivo for your comments and your time. It is exactly what I needed to improve ! I did not knew if the problem was from my data set or from its development. Now I know Yes my flats were not correct and I will try longer exposures. I understand that the signal/noise ratio is greatly improved with longer exposures. What would you recommend: 2 minutes ? I am still confused about the ISO to use, even after a careful reading of this article http://dslr-astrophotography.com/iso-ds ... otography/ With my camera (nikon D5600) if I understand well it is of no use to increase the ISO above 200 which seems quite low to get a signal with a galaxy.
It might be that the sky will be clear here tonight. If so I will give a new try.
Thanks again