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Crescent Nebula. Potential banding?

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#1 McConkey

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Posted 06 August 2014 - 06:34 PM

33 x 240s ISO800. 450d modded. Bias, Darkss and Flats added

   The moon and red zone didnt help but i got what i could.

I noticed theres some crazy (what i think) is banding. I added an ultra stretched version to highlight it. Does anyone know what causes it? Is it noise? LP? I use the CLS clip in LP but ive noticed it in my last few images. Darks were same temp as sensor, 22.0 to 25.0 degree's. Any ideas?

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Edited by McConkey, 06 August 2014 - 06:35 PM.


#2 Jerry Lodriguss

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Posted 06 August 2014 - 11:43 PM

There is a lot of faint red emission nebulosity in that area, and some of what you have there is real, but it does look like maybe you might have some banding also, which is really weird.

 

I would look at the flats first... maybe process your images without them and see what happens.

 

I reprocessed your image to tone down the stars and make the nebulosity red instead of orange... I hope you don't mind.

 

Jerry

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#3 McConkey

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Posted 07 August 2014 - 01:38 AM

lol Jerry, you could walk into my house and take the dinner from my plate and i would be greatful. Having you take time out of your schedule to look and do a quick re-process is greatly appreciated! You re-process looks vibrant and cleaner. I guess you've been reading your own books :)  

    I re-stacked with no flats, added an artificial flat and re-processed. The image was slightly cleaner but the "lines" are still present. I know the area has a dusting of red but i'm always cautious when i see straight lines like i see in the image, straight lines are man made  :p
 
Astrobin is down right now so i cant upload but here's the re-processed with no flats and ultra stretch to bring out banding.

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Edited by McConkey, 07 August 2014 - 01:42 AM.


#4 bouffetout

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Posted 07 August 2014 - 01:15 PM

Seriously dude ,I don't see it as banding .... nice shot !



#5 McConkey

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Posted 07 August 2014 - 03:39 PM

Appreciate the vote of confidence! I'd like to get more hours on this target and see what else i can bring out.

   Karl



#6 Jerry Lodriguss

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Posted 07 August 2014 - 04:42 PM

There's a bunch of red stuff that's now gone on the right side of the image.

 

Whey don't you try one with no flat at all.

 

Jerry



#7 McConkey

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Posted 07 August 2014 - 06:47 PM

No flat, no cropping. Just a quick process. I am happy with how it turned out so far. Going to try and grab some more lights of this to increase the SNR and see if that'll help.

 

Jerry - Why a flat would cause the banding? Flats were taken during same session, same camera orientation, temp etc

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#8 Jerry Lodriguss

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Posted 08 August 2014 - 01:00 AM

No flat, no cropping. Just a quick process. I am happy with how it turned out so far. Going to try and grab some more lights of this to increase the SNR and see if that'll help.

 

Jerry - Why a flat would cause the banding? Flats were taken during same session, same camera orientation, temp etc

 

Hi Karl,

 

It depends on how you take your flats and what the light source is.

 

Remember in the old days of Television with cathode ray tubes?  If you took a picture at a shorter exposure than the scan rate, you would get diagonal lines in the image.

 

I've seen bands in some flats I have taken that were illuminated with an LCD screen.

 

Probably not a similar process happening between a CRT and an LCD, and I don't understand the electronics of how an LCD works, but there are plenty of things that go wrong with flats.

 

Try taking your flats and using the Eqaulize command in Photoshop.

 

I'm not saying the banding is definitely from your flats, I'm just saying that's the first thing I would look at.

 

And it looks like you still have the problem in the last pic you posted without any flats at all, so it's probably not the flats.

 

Some of the old 20Da cameras had a problem called the "dark river" which were dark bands that looked something like what I see in the last image you posted. It was a nightmare to get rid of.

 

There's plenty of things that can go wrong with the sensor and electronics in these cameras. It's a wonder that more stuff doesn't show up in the crazy stuff we shoot.

 

Jerry



#9 McConkey

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Posted 08 August 2014 - 02:53 PM

Awesome info Jerry, thanks.

   I used the good old white t-shirt at mid day for my flats, but that's really to know about the banding from LCD,s. It makes sense.

I took a look at the darks i used from that imaging session, the temperature ranged from 20.0 degree's to 29.0 degree's while the lights were 24.0 and 25.0 degree's. I think i may have matched the temps wrong with the darks and perhaps that could have caused the weird artifacts? 

 

Here's a stretch of the highest temp dark and lowest temp dark from that night.

 

Will re-stack and try again, paying attention to dark temp this time.

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#10 Jerry Lodriguss

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Posted 08 August 2014 - 05:02 PM

Hi Karl,

 

I don't think that mis-matched darks are going to give you banding like that.

 

Mis-matched darks will give you dark holes or light spots where the individual pixels are in an individual calibrated light, and then they may get smeared when the frames are aligned for stacking.

 

Jerry



#11 McConkey

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Posted 08 August 2014 - 05:30 PM

Good to know. Really appreciate all the help you've given. I think it might just be the sensor of my 450d. Looking back and over stretching my last few images it's clearly in the exact same spot everytime. I recently modded it so i'm wondering if the extra sensitivity is causing it to be more pronounced. I'm looking to upgrade to either the 6d or ccd anyway by Christmas time :p looks like this justifies my need to upgrade :)



#12 Tonk

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Posted 08 August 2014 - 06:45 PM

Just a thought .. I've had very very similar banding after I accidently included a single light in one of my calibration sets (darks/flats/bias forget which) . Worth a check?



#13 McConkey

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Posted 09 August 2014 - 12:55 PM

Tonk - Checked the bias/darks/flats. no light images but definitely worth the check. I re-stacked with no calibration sets, just lights and there was a fairly big difference. It was barely visible, still there but hard to see even with over stretching.

 

It's been clear all week, literally every night since Monday and of course i've been on nights this week so no chance to try another object and see whats up. I'm also thinking it could be the temperature. It was mid to high 20's outside during the night and the sensor reached 29.0 degree's for some of these darks and lights, it was just so damn hot and humid. Its dropped to about 9 - 12 degree's at night now so huge difference.

 

Appreciate all the helpful ideas!








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