M76, the Little PEST nebula!

[ollypenrice]

'Little Dumbbell' my foot: it's worse than a little pest, this one. I've never imaged it before and have always been struck by the fact that it rarely looks the same in any two renditions. Now I know why! It's very tricky. This is a WIP since I was also battling the data. There was differential flex in the dual TEC meaning that the Ha side was affected by slight trailing. For some reason the darks on that side clipped the Ha but not the RGB so I used a bias only on the Ha, which was also noisy as a result. These things are sent to try us. Plus the wind kept nudging the Mesu's elbow etc etc. However, I was anxious to play with what we had so this is the result. (About Four hours each Ha and OIII and 80 minutes per colour.)

The object has an extremely high dynamic range so I needed two distinct stretches both in Ha and OIII. I used Ps layer masks to blend them. Trying to retain detail in both the outer wisps and the core took a ridiculous amount of effort. It's also unreasonably small! Anyway, here it is for now but I really want to nail this little devil when I've sorted out the technical issues.

Olly

 

[Kinch]

Obviously a lot of effort for you but it has paid off  👍 - even if you think this is still a WIP. I remember trying it once and just 'walked away' from it .  (I would need an extender and extremely good conditions to even think about it again).

[AstroNtinos]

Nice little target. Good job

[Laurin Dave]

Very nice Olly, maybe try adding a Pedastal when you calibrate to prevent black clipping.  ASI1600 users have to do this (well I do) to prevent the same.  It's there in AstroArt somewhere.   

Dave

[ollypenrice]

57 minutes ago, Laurin Dave said:

Very nice Olly, maybe try adding a Pedastal when you calibrate to prevent black clipping.  ASI1600 users have to do this (well I do) to prevent the same.  It's there in AstroArt somewhere.   

Dave

Thanks Dave. What baffles me is why it only happened to one dataset and has been running normally with the same darks till yesterday. It's not called a dark art for nothing!

Olly

[Laurin Dave]

Yes its all very mysterious, how can a dark have a higher level than a light?   Who knows but on occasion they do.   Was that with the 460, you've mentioned before how dark the background is with that camera so maybe its pretty close to clipping even on LRGB,  clearly your skies are too dark!   In Pixinsight you can use PixelMath to add a small pedastal to your integrations which will move the histogram to the right. 

Dave

[ollypenrice]

24 minutes ago, Laurin Dave said:

Yes its all very mysterious, how can a dark have a higher level than a light?   Who knows but on occasion they do.   Was that with the 460, you've mentioned before how dark the background is with that camera so maybe its pretty close to clipping even on LRGB,  clearly your skies are too dark!   In Pixinsight you can use PixelMath to add a small pedastal to your integrations which will move the histogram to the right. 

Dave

No, it was with the Moravian and its 8300 chip. The clipping by the dark was enough to bite into the faint data. Applying our existing darks simply trashed the stack. Even using the 10 minute dark on the 15 minute subs produced the same effect. In the end I just used a master bias but I'll need to shoot new darks. However, the RGB from the following night stacked normally. I've checked the data in the FITS headers and found nothing abnormal (temperature being the one I suspected.) All was as usual... I'll try stacking in a different instance of AstroArt on another PC.

Olly

Edited November 20, 2020 by ollypenrice

[Laurin Dave]

I have found that with my KAF16200 chip I need to refresh my darks about every 2 months or I get noise pattern issues on Lum and Ha, but never on RGB, probably because they're never stretched hard enough to show.. unfortunately I only found this out after having the camera 18 months..  I seem to remember Brendan reporting that he'd seen something similar with his 16200 camera, which was what put me onto it..    Infuriating! 

Dave

[Kinch]

3 hours ago, Laurin Dave said:

I seem to remember Brendan reporting that he'd seen something similar with his 16200 camera

Dave:   Yes - I found that a problem I had was overcome with new Darks....and.....that the problem seemed to be resurfacing some time later again. (I cannot expand on what "some time later" actually means - I am not sure). I did not continue and follow up to pinpoint the problem (I changed camera for an unrelated reason - and have not yet put the 16200 camera back on). I suspected at the time (for lack of another explanation) that perhaps the ambient temp. was the root cause - i.e. the differing loads on the TEC. I hope I don't have to do DARKS every two/three months.....but if that keeps things OK....then I will. However, perhaps a set for a particular temp. range can be used for more than just one 2/3 month period.........depending on the ambient temperature.

[Laurin Dave]

1 hour ago, Kinch said:

Dave:   Yes - I found that a problem I had was overcome with new Darks....and.....that the problem seemed to be resurfacing some time later again. (I cannot expand on what "some time later" actually means - I am not sure). I did not continue and follow up to pinpoint the problem (I changed camera for an unrelated reason - and have not yet put the 16200 camera back on). I suspected at the time (for lack of another explanation) that perhaps the ambient temp. was the root cause - i.e. the differing loads on the TEC. I hope I don't have to do DARKS every two/three months.....but if that keeps things OK....then I will. However, perhaps a set for a particular temp. range can be used for more than just one 2/3 month period.........depending on the ambient temperature.

I asked SX about it and they said it was normal for that sensor, so now I do them every 6-8 weeks..  overnight when its cloudy so plenty of opportunity !

[Kinch]

12 hours ago, Laurin Dave said:

normal for that sensor

Wow!....Wish I had known that much earlier. Like you, I have been working with this chip for some time and was scratching my head over what I saw. Now that I know for sure (apparently), there will be no problem taking new Darks every so often. Thanks for that info - now that I have a remedy (I hope), all is good with the world again. 😏

Edited November 21, 2020 by Kinch
Darks - not Flats

[emyliano2000]

I love the colour and the details in the central part. I had a go at it too in HOO at the beginning of the year but being in a light polluted area I need much longer integration time (this one is roughlt 30 hours). Mine came out quite blue/cyan

Emil