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AbsolutelyN

M81 + M82 with Esprit 100

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This is my first attempt at a really long exposure, it's a combination of the odd clear night since Feb this year. Processing it has been a steep learning curve and I'm sure it could be done far better. I've found calibration of the 1600pro hard and still have not really fully sussed it ... but getting closer. Probably mostly as calibration is a completely new concept to me. I believe it's in the 26 hours region .... and suspect I've been too rough on the blacks and clipped them but it was an uneven background probably caused by bad calibration (or hazy skies). Anyway, it was good fun learning. Any feedback appreciated as keen to make improvements. Esprit 100, ZWO1600Pro, ZWO filters.

Changes in second image.
Further changes in third edit of this image!

https://www.astrobin.com/full/401219/0/?nc=user

M81+M82_APRIL_2019_B.jpg

M81+M82_APRIL_2019_c.jpg

M81+M82+IFN+FINAL.jpg

Edited by AbsolutelyN
Third image revision
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Good one. The background looks a bit green to me but that's an easy fix.

I would resist at all cost the temptation to use the black point to flatten the sky. It will inevitably cost you faint data and is not very effective either. What software do you use? If Pixinsight then DBE should do it. If Photoshop you could try the Gradient Xterminator plug in from Russ Croman.

Olly

Edited by ollypenrice
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Thanks Olly, didn't spot that. It's a got green/cyan cast in the blacks. It's had ABE in PixInsight and then I've also manually done a gradient removal with Apply Image with Subtration in Photoshop as there was still loads of gradients left after the ABE. I'll look again at that as perhaps it's too heavy handed. I'll have another go at reprocessing at some point as learnt so much from this one image I bet I can improve in it already ... I think this is attempt 5 at processing it! The first 4 were truly awful.  

Edited by AbsolutelyN

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54 minutes ago, AbsolutelyN said:

...uneven background probably caused by bad calibration...

Looking good. Since you have 26 hours of data I suspect you may have picked up the IFN. There is a lot of dust in that region of the sky which scatters starlight, here's a wider view:

spacer.png

The dust mostly scatters blue light, so checking that channel may be one way to distinguish IFN from calibration problems.

Edited by Knight of Clear Skies
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I was hoping for IFN but I don't think I have it. As my calibration is so bad and I don't have usable flats for half the data I think I'm lucky to have cobbled this together. I will reprocess though as maybe more can be extracted with better processing. I'm redoing the darks now as I don't think the originals were quite right. 

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You're right ... there is IFN! Slightly on blue but definitely visible on Luminance as it matches with IFN on other Astrobin images. I clearly need to be far more careful with the dark areas of the image. Next challenge is figuring out how to process it.

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22 minutes ago, AbsolutelyN said:

Thanks Olly, didn't spot that. It's a got green/cyan cast in the blacks. It's had ABE in PixInsight and then I've also manually done a gradient removal with Apply Image with Subtration in Photoshop as there was still loads of gradients left after the ABE. I'll look again at that as perhaps it's too heavy handed. I'll have another go at reprocessing at some point as learnt so much from this one image I bet I can improve in it already ... I think this is attempt 5 at processing it! The first 4 were truly awful.  

I would advise DBE over ABE. On this kind of image ABE is likely to read the 'background sky' where it is too close to the galaxies and so over-correct and create dark rings around them.  The trick with DBE is not to put in too many markers and to keep them well away from any galaxies and, of course, stars. You may need to crank up the 'tolerance' value from the default of 0.5 in DBE but in extremis just make it as high as it needs to be to get the markers accepted. I wouldn't use DBE to kill the green off entirely: that's best done afterwards in SCNR green.

Olly

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Thanks Olly, much appreciated. Starting reprocessing already so will give that a go.

Edited by AbsolutelyN

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The only technical assistance I can give is ......   " Wow !! that's a beauty !!...".

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Very nice indeed.  I have exactly the same kit but your image is way better than anything I have achieved!

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15 minutes ago, wornish said:

Very nice indeed.  I have exactly the same kit but your image is way better than anything I have achieved!

Stick with it ... for me the SGP and the sesto senso has made a massive difference. Wish I had the EWF7 and bigger filters, I wish I'd gone with 2" filters over 1.25 as have huge amounts of vignetting and I'm struggling with the flats!

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Re-processed with advice from above - many thanks for the input and hopefully a bit better? I think there is a small amount of IFN in the background, though how much of it is real I'm not certain. This is approx 4 hours less exposure to exclude some frames at a completely opposite orientation which made gradients far worse.  

M81+M82_APRIL_2019_c.jpg

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Final version ... managed to get better calibration and extract better IFN. Obviously needs a lot more exposure and better technique as pushing the data too far but quite pleased it is visible and great learning curve to extract it!

M81+M82+IFN+FINAL.jpg

Edited by AbsolutelyN
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