M31 - high expectations, not great result

[MKR]

Hi all,

I've got a clear night yesterday so thought I'll have a go on M31 for the first time. I took 20x120' ISO 800 with EOS 5D mk IV, guided, dithered. Processed with flats and around 40 matched bias frames. Stacked and processed in Siril. I can tell that something isnt quite right with my flats, but other than I was expecting a bit more. I'm imaging from Bortle class 5.

Can this be processed significantly better? Looking at astrobin people get much better results with 1h worth of data with similar cameras. I do know that my stars aren't great on edges - I don't have a coma corrector on my SW, 200P - just trying to focus on details/colours for now. It was quite a hot night (> 20C), so maybe this is one of the reason?

Many thanks.

Autosave.fts

[powerlord]

quick go in startools. definitely more in there.

[alacant]

Hi

Amazing detail for just an hour:)

I'm with @powerlord; there's more to be had. But a few points:

You've lost a lot of the galaxy. don't forget to allow for the fainter stuff.

200p so you're going to need a larger secondary to cover the 5d frame. A swap with someone with the 58mm secondary from a pds works well. Up to aps-c, they don't need the larger mirror.

There's loadsa curvature and in so correcting, some of the frame is lost. A cc would help you take true advantage of full frame.

There's banding in the red. It might be a good idea to correct that in Siril before registration.

With light pollution your gonna need quite a bit more than an hour.

Don't forget to dither between frames

Cheers and HTH

 

 

 

 

 

Edited September 8, 2021 by alacant
traducción

[ollypenrice]

Your histogram tells a story:

The peak in the Levels graph is made up of the galaxy itself. The flat line to its right is from the stars. In the original data that peak would have had a left hand side rising gradually, not unlike a mirror image of the right hand side. However, in moving the black point slider too far to the right you have thrown all those faint data away. This is called black clipping and most newcomers to AP do it. It cannot be recovered other than by going back to the original and stretching from scratch.

Olly

[alacant]

7 minutes ago, ollypenrice said:

It cannot be recovered other than by going back to the original

... or using an app which obviates the need to have to do so.

Edited September 8, 2021 by alacant

[powerlord]

how are you knowing how much curvature to correct there alacant ?

 

stu

[alacant]

1 hour ago, powerlord said:

how much curvature

Pinch until the stars elongate at 90° then back off until they're circular. 

HTH

EDIT: IIRC there are other ways of using the Lens module. I'm certain @jager945 could explain far better than I.

Edited September 8, 2021 by alacant

[vlaiv]

47 minutes ago, alacant said:

There's loadsa curvature and in so correcting, some of the frame is lost.

What type of curvature are you talking about?

[MKR]

Thank you for all the good advice. It's true, I did clip it. I couldn't find any other way to get rid of this "ugly" sky outside of the M31. What do you do with this? How can I get rid of this this grey area? Is it just the noise which should go away with more and more subs? Or maybe the only way around it is with masks? I'm yet to master PS, which would be my software of choice, as learning it would be also beneficial for my other photography work. Thanks again.

[Iem1]

Hey man, I am a beginner to processing images myself, but I had a go in PS. I struggled to keep colour balance under control (Still not fully under control lol) and I couldn't do much more stretching before completely blowing out the image.

Hopefully some of the skilled people will be able to help you out a bit more, but it is a nice image! Dust lanes look nice  

 

[tomato]

There are plug ins for PS which will sort out the back ground, (one called Gradient Exterminator springs to mind) and I think there are workflows on the internet that show how this can be done just with PS. Sorry I can’t provide more detail but I haven’t used PS in quite a while.

I think you have had a good first go at M31, I certainly wouldn’t class it as an easy DSO imaging target.

[vlaiv]

Yes, flats are not quite good. Here is what I managed to pull out

[MKR]

Hi All,

Many thanks everyone. I did not forget about this thread. Instead, improved my processing skills slightly and gathered one more hour of exposure. Here's my result with 2h of data. Dithered, no darks - bias with improved flats (still not perfect though). I am reasonably pleased with it now. Thanks again for help!

PS I am aware of the burnt out core, I'll do better next time! Not sure what's this vertical banding on the right side - but I've found a thread of someone reporting a similar problem on the same ISO (800), the same camera. I might try to change ISO for the flats.