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Second attempt M31 !

Newfie

By Newfie
in Imaging - Deep Sky

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Newfie

Newfie

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After a fairly long lay off I have now managed to waterproof the observatory so I thought I would have another go at M31, although it was that long ago I think I can claim it as a first attempt. It was kind of thrown together with around 10 lights between 30 and 300 seconds and 6 darks not taken at the same time oops I know thats wrong. Anyway any advice and pointers welcome. It was taken with a 90mm ts refractor and a Canon EOS1100 modified.

m31 jpeg (1 of 1)-2.jpg

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gnomus

gnomus

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Hi Newfie

It is a pretty good attempt at M31 given such limited data.  I like that you shot some darks.  Did you shoot any bias frames?  These are easy to do and you can reuse the Bias master once you've stacked it.  It looks to me like you didn't shoot any flats.  These are very important and may have helped with the dust spots you have and the vignetting.  I would always use bias and flats.

You have a bit of a gradient in there  - it is green up in the top right corner and red in the bottom left.  Everyone who shoots RGB images gets these gradients.  Your image will improve if you can find a way to eliminate them.  I use DBE in PixInsight.  Others use Gradient Exterminator in PS.  I haven't used Gradient Exterminator so cannot comment on it.  

I hope that is the sort of thing you were looking for.  It is great that we can get shots like this from our back garden, isn't it?

 

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Newfie

Newfie

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No that's exactly the kind of feed back I was hoping for . No I didn't take any flats I'm just trying to work out the best way to take them nor did I take any Bias frames . I will try with both on my next attempt and thanks for the pointer towards removing the gradient I will have a look in photoshop gradient exterminator. I did notice the dust marks spots / marks at the top of the Image and wondered how best to remove them ! 

Again thanks very much.

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gnomus

gnomus

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1 hour ago, Newfie said:

No that's exactly the kind of feed back I was hoping for . No I didn't take any flats I'm just trying to work out the best way to take them nor did I take any Bias frames . I will try with both on my next attempt and thanks for the pointer towards removing the gradient I will have a look in photoshop gradient exterminator. I did notice the dust marks spots / marks at the top of the Image and wondered how best to remove them ! 

Again thanks very much.

Gradient Exterminator is a Photoshop plug in: http://www.rc-astro.com/resources/GradientXTerminator/

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Horwig

Horwig

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Hope you don't mind, I'm not claiming to be any good at processing,  but love playing with images to see what's there.

Anyway, this is Gradient exterminator, HLVG, with masks and layers in photoshop, I think you have a half decent M31 there with such little data.

m31a.jpg

 

Cheers

Huw

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Newfie

Newfie

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Sorry to seem like an idiot but when you suggest try stacking without the darks did you mean on my original image, and how many darks would you think I should  have taken.

Many thanks

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Knight of Clear Skies

Knight of Clear Skies

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Just now, Newfie said:

Sorry to seem like an idiot but when you suggest try stacking without the darks did you mean on my original image, and how many darks would you think I should  have taken.

Many thanks

No problem, it's all part of the learning curve of AP. :)

Yes, I'd suggest trying stacking just your lights and see if it comes out any better. DSLR darks can be a bit tricky, they can help but can also introduce additional noise if the temperature profile doesn't match the lights. In terms of numbers I'd think at least a dozen, with 20-30 being better if practical.

The importance of darks is often overstated, personally I only take them if it's convenient. In most situations I'd prefer more lights if there is a choice between the two. Dithering (moving the aim point a few pixels between exposures) and a Kappa-Sigma clip when stacking are very effective at removing DSLR noise patterns.

Hope that's some help.

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gnomus

gnomus

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I agree with Knight.  DSLR darks are awkward.  They need to be at the same temperature as the lights, but even then how do you know.  I go for 25.  Bias frames are straightforward (and you could do them now for your M31 image).  I stack 200 bias frames.  Flats are important too - again I stack 25 or so.   If you haven't taken the camera off your scope (you say you have an observatory) you could shoot flats now. 

What would also help is more subs.  Less than an hour is being a bit optimistic.  The joy of an observatory is that you can leave things set up and so you can have the same framing over several nights.  2-3 hours and it will start to look quite nice.  10 hours and you may get something rather special.

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Davey-T

Davey-T

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The number one thing you need to do when imaging with a DSLR is dithering the next most important thing is dithering around a dozen pixels or 2 or 3 average star diameters.

This is a crop of your background, dithering will help remove the coloured mosaic.

Dave

Non dithered.PNG

Second time today I've been unable to edit a post properly ?

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Newfie

Newfie

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Guys thanks for all the advice I was happy with the reply until I reached the last few lines "Dithering" I have never even heard this before and Kappa Sigma ! Now off to Google them so I have some idea of what they are.

I do have the scope set up in an observatory so I should be able to get the darks at the correct temperature if its needed and the flats I have read so many different versions on how to take them. I have been looking at ways to do these with some form of DIY approach.

One of my dogs decided to eat the cables running to the observatory and it has had a fairly serious leak so it's kind of been of of action for around a year. I am now back up and running so am looking forward to some clear nights to try your invaluable and welcome advice.

Cheers Guys

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ollypenrice

ollypenrice

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23 hours ago, gnomus said:

Hi Newfie

It is a pretty good attempt at M31 given such limited data.  I like that you shot some darks.  Did you shoot any bias frames?  These are easy to do and you can reuse the Bias master once you've stacked it.  It looks to me like you didn't shoot any flats.  These are very important and may have helped with the dust spots you have and the vignetting.  I would always use bias and flats.

You have a bit of a gradient in there  - it is green up in the top right corner and red in the bottom left.  Everyone who shoots RGB images gets these gradients.  Your image will improve if you can find a way to eliminate them.  I use DBE in PixInsight.  Others use Gradient Exterminator in PS.  I haven't used Gradient Exterminator so cannot comment on it.  

I hope that is the sort of thing you were looking for.  It is great that we can get shots like this from our back garden, isn't it?

 

The perfect analysis.

Olly

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