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m31 colour

alacant

By alacant
in Getting Started With Imaging

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alacant

alacant

Posted
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Hi everyone. Here are two snaps. 12 x 240s and 36 x 240s, the latter uses the first set. I then added more the next night. I don't see much difference in the -bad- noise but what is surprising is that I can get colour in the longer version. Is there any way I can get the same colour with the shorter exposure? It's a 700d with StarTools and gimp. TIA.

m31.jpg

m31-4.jpg

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Thalestris24

Thalestris24

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Hi

Not sure what you mean... Both images are colour - but different. The first is too red. The second is better in some ways but perhaps a bit too yellowish. Don't forget to align the histogram peaks to get the colour balanced. I've seen a number of tutorials around specifically for help in processing M31 and other galaxies. Of course, you need lots more data to do the target justice!

Louise

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alacant

alacant

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15 hours ago, Thalestris24 said:

Not sure what you mean...

Sorry. Not very well explained. More data seems to mean more colour. I was wondering if it be possible to obtain the same colour with fewer light frames, hence:

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 Is there any way I can get the same colour with the shorter exposure? 

TIA.

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Thalestris24

Thalestris24

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Just now, alacant said:

Sorry. Not very well explained. More data seems to mean more colour. I was wondering if it be possible to obtain the same colour with fewer light frames, hence:

TIA.

Hi

Hmm... Well, galaxies aren't very colourful things, especially not with an unmodded dslr. But they do tend to have bright cores and faint dust lanes. If you can get enough data to show all the dust lanes any colour will also be there in the stacked image. M31 is much bigger than people think but the outer dust lanes are faint. The detail is in the luminance. I think it was last year that Olly made a 40-something hour M31 which was amazing - a gold standard!

Louise

 

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alacant

alacant

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4 hours ago, Thalestris24 said:

40-something hour M31

Ah, OK. Only 39 1/2 hours to go then! But seriously. I seem to have the same detail in both. It's a pity it seems to take three times more frames to get colour into the thing.

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Thalestris24

Thalestris24

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39 minutes ago, alacant said:

Ah, OK. Only 39 1/2 hours to go then! But seriously. I seem to have the same detail in both. It's a pity it seems to take three times more frames to get colour into the thing.

I'm pretty sure there's a lot more detail to be acquired! At a guess, you probably need to think in terms of at least a couple of hours worth depending on your skies and f-ratio :) 

Louise

Edit: If you haven't seen it, read Sara's post in this thread 

 

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ollypenrice

ollypenrice

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Colour, like faint nebulosity, takes time. There are processing tricks to pull out more colour without increasing noise (noting that using the saturation tool is a terrible noise booster) but in the end it is down to time. In recent projects I've given more time over to shooting colour and I won't be skimping on it again.

BTW, I have enough data on M31 to sink a ship and am happy with some aspects of it but I still don't like my colour! I can't lose the cyan domination of the blue channel whatever I do and have gone into a long term sulk over this...

Olly

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alacant

alacant

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Hi again. Yes, I'm convinced about the amount of data. I'm up to 90 minutes and both colour and detail are emerging. There's still a lot of noise, almost certainly my total lack of understanding of the order of application of the infinite combinations of StarTools' variables. Anyway, I hope you'll agree that there has been some improvement, if not in noise, at least detail and colour. Thanks for looking and any comments for where to go next most welcome. Clear skies and TIA.

m31-larga.jpg

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alacant

alacant

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On 12/11/2016 at 19:28, Thalestris24 said:

a couple of hours worth depending on your skies and f-ratio

Thanks for the guideline. I'm still not at the magic 2 hours yet but I'm convinced about the amount of data. My most recent attempt is 90 min f5. Previously I had about 50 mins f8 [1]. I prefer the margins on the latter, a takumar 300mm. A real piece of glass if ever there was one.

[1]May have been 5.6. One of the click stops on the aperture ring anyway.

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Thalestris24

Thalestris24

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1 hour ago, alacant said:

Ah. OK and thanks for looking. Can you give me a one liner on that or is it a case of experience? TIA.

Hi

It's just a matter of adjusting the histogram level just right so there's no clipping. This Doug German video shows you.

Um, however, did you say you were using StarTools? Can't remember how that does it but you can certainly adjust it in Gimp using the levels tool.

Louise

ps you can also get clipping and add unwanted noise by adjusting the contrast too harshly. It's hard to tell but I think your image only needs a slight tweak to get it right. Disclaimer: I'm not the best judge of these things myself!

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alacant

alacant

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24 minutes ago, Thalestris24 said:

I'm not the best judge

I'm certain you're a lot better than I. Here's gimp, although I think the damage has already been done. I know I got the star mask wrong for a start. Maybe I'll need to start over from the fits...

fss.JPG

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alacant

alacant

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Still can't get the levels, but I think this is without the clipping you mentioned. I've lost the sharpness but got a bigger galaxy. Still noisy. Gonna get more data toward the 2 hour target asap. Not easy this AP stuff!

fss2.JPG

m31-6.jpg

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