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Astrophotography and Sketching >> DSLR & Digital Camera Astro Imaging & Processing

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srosenfraz
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Re: I am doing something very very wrong new [Re: mmalik]
      #6119911 - 10/06/13 12:52 AM

I agree with Mike about there being something wrong with this data. I have the same color gradient issues when I try to do a DDP stretch, and the image has extremely low contrast.

You've fundamentally done all the right things - captured a good amount of data, have reasonable number of calibration frames, etc. It feels like something may have gone haywire along the way.

A few questions -

1) With your flats - is the orientation of the camera unchanged from the time you take your flats until the time you start capturing?

2) When you captured your flats, did you have the CLS filter in place (and left it the same until you were capturing data)?

3) When applying your calibration frames in DSS - are you sure you have all of the correct frames in the right place (i.e., you didn't swap dark frames for flats, or some other type of mistake)?

4) Would you mind posting one raw .CR2, your Master Bias, Master Flat, and Master Dark frames?


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ebacon
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Reged: 02/13/13

Loc: Rochester Hills, MI
Re: I am doing something very very wrong new [Re: srosenfraz]
      #6120151 - 10/06/13 07:53 AM

I am learning from this thread, too.

What are calibration frames? Is that a generic term for the groups of flats, bias, and darks?

Thanks!


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Footbag
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Re: I am doing something very very wrong new [Re: ebacon]
      #6120250 - 10/06/13 09:29 AM

Quote:

I am learning from this thread, too.

What are calibration frames? Is that a generic term for the groups of flats, bias, and darks?

Thanks!




Yes. Flats, darks and bias are calibration frames.


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shawnhar
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Re: I am doing something very very wrong new [Re: Footbag]
      #6120513 - 10/06/13 12:23 PM Attachment (8 downloads)

I'm gonna guess one of 2 things....
1st, this image was taken through clouds, maybe high thin clouds you couldn't see, but that is the most likely case. I have had the same thing happen, flat's can't fix it because the gradients are changing frame to frame.
2nd and hopefully less likely, you have crazy multiple light sources around like neighbor lights or you are shooting through/close to light sources. Flats can't fix that either because the target is moving, therefore the gradients are moving frame to frame.
I gave a go in Star Tools but like Ivo said, very difficult to doa anything with it in post processing, those gradients are pretty rough. I tried using masks for the galaxies and "isolate" in the Life function.


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petemumbower
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Reged: 07/12/09

Loc: West Michigan
Re: I am doing something very very wrong new [Re: shawnhar]
      #6120651 - 10/06/13 01:56 PM

How does the each frame look after calibration before stacking? I want to agree that maybe high thin clouds are present.

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Tonk
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Re: I am doing something very very wrong new [Re: petemumbower]
      #6120689 - 10/06/13 02:18 PM

Quote:

I'm gonna guess one of 2 things....
1st, this image was taken through clouds, maybe high thin clouds you couldn't see, but that is the most likely case. I have had the same thing happen, flat's can't fix it because the gradients are changing frame to frame.
2nd and hopefully less likely, you have crazy multiple light sources around like neighbor lights or you are shooting through/close to light sources. Flats can't fix that either because the target is moving, therefore the gradients are moving frame to frame.
I gave a go in Star Tools but like Ivo said, very difficult to doa anything with it in post processing, those gradients are pretty rough. I tried using masks for the galaxies and "isolate" in the Life function.




1 thing wrong here and a solution

1) Flats are never to be used to correct for sky gradients - what you are describing is not a optical transmission issue so flats are totally inapropriate

2) The correct way to correct external gradients is to use a subtractive process using tools such as Russel Croman's GradientXTerminator or one of the Background Extraction tools found in PixInsight or Images Plus.

The fact that the gradients change during the imaging session is immaterial as the correction is performed on the final stacked image, usually right after the initial stretch

I suggest you read Russel's tutorial to gain an understanding of what needs to be done

http://www.rc-astro.com/resources/GradientXTerminator/tutorial.html

As I said there are a selection of astro-image processing applications that provide specific solutions


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ICallHimGamblor
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Reged: 06/24/13

Re: I am doing something very very wrong new [Re: srosenfraz]
      #6120899 - 10/06/13 04:23 PM

Quote:


A few questions -

1) With your flats - is the orientation of the camera unchanged from the time you take your flats until the time you start capturing?

2) When you captured your flats, did you have the CLS filter in place (and left it the same until you were capturing data)?

3) When applying your calibration frames in DSS - are you sure you have all of the correct frames in the right place (i.e., you didn't swap dark frames for flats, or some other type of mistake)?

4) Would you mind posting one raw .CR2, your Master Bias, Master Flat, and Master Dark frames?




Thanks for continuing to help diagnose this. To answer your questions:

(1) The camera orientation had not changed.
(2) The LP filter was in place for the flats as well as the images. I'm hoping CLS filter=LP filter
(3) I am pretty sure I put the calibration frames in the right place, but I will check again.
(4) I have added the calibration frames and a random sub to this folder: https://drive.google.com/folderview?id=0By0hG91nGRL9ckxUeXAxUXdTLTQ&usp=s...

Let me know if that doesn't give you the access you need.

Since there is such an emphasis on my flats, I will explain what I did to capture them... They are t-shirt flats captured in the early evening before an imaging session. I had the camera on manual and used BackyardEOS to capture them and I tweaked the exposure time until the histogram was approx halfway. That's how a couple threads on this site said to make them.

I hope I'm not embarrassing myself with my noob-ness.

Thanks everyone for y'alls help.


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ICallHimGamblor
super member


Reged: 06/24/13

Re: I am doing something very very wrong new [Re: shawnhar]
      #6120905 - 10/06/13 04:28 PM

I would be surprised if it was a high-clouds issue. I have this problem with every imaging set I have ever taken, including four different nights over the past week or so on different targets.

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mmalik
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Re: I am doing something very very wrong new [Re: ICallHimGamblor]
      #6120917 - 10/06/13 04:33 PM

As a control test, have an ICNR session to rule everything else out, other than calibration. Thx

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shawnhar
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Re: I am doing something very very wrong new [Re: Tonk]
      #6121105 - 10/06/13 06:42 PM

Thanks Tonk!

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ICallHimGamblor
super member


Reged: 06/24/13

Re: I am doing something very very wrong new [Re: mmalik]
      #6121123 - 10/06/13 06:53 PM

Quote:

As a control test, have an ICNR session to rule everything else out, other than calibration. Thx




I know what some of these words mean.


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Tom and Beth
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Reged: 01/08/07

Loc: Tucson, AZ
Re: I am doing something very very wrong new [Re: ICallHimGamblor]
      #6121128 - 10/06/13 06:56 PM

[quote
(Big SNIP)

hope I'm not embarrassing myself with my noob-ness.






As a relative noob, I doubt very much you are embarrassing yourself. I bet there's a few learning from the replies and help you're getting. I know I am.

Edited by Tom and Beth (10/06/13 06:57 PM)


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akulapanam
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Reged: 08/27/12

Re: I am doing something very very wrong new [Re: Tom and Beth]
      #6121175 - 10/06/13 07:30 PM

A couple of suggestions:

First don't save your file from DSS instead make a copy of the autosave.tif and then use imagemagick to convert it to 16 bit. My understanding is that DSS has a bug in the 16bit save routine.

Second I think you would be better off without the CLS even if you have to reduce exposure per shot. For me the CLS filter tends to result in a product with bad color cast and requires a large increase in total exposure time.


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akulapanam
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Reged: 08/27/12

Re: I am doing something very very wrong new [Re: akulapanam]
      #6121200 - 10/06/13 07:49 PM

Also having downloaded your actual file:

As other have mentioned the focus is not great on this image.

The gradient issue looks complex and a lot like the challenges I have faced. I have similar equipment and I wish I had a solution but I don't.

Overall I think you are probably being a little hard on yourself this is a pretty nice picture and looks a lot like some of the photos I have taken. The biggest challenge people who live in a light polluted environment with time constraints have is getting enough exposure time. For me the solution was to go with hyperstar.


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srosenfraz
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Re: I am doing something very very wrong new [Re: ICallHimGamblor]
      #6121218 - 10/06/13 07:59 PM

I think I see the problem. Your "Master Offset" file doesn't look like its taken correctly. A Bias frame (or offset) is a frame that it taken for the least possible time with the camera covered (usually around 1/4000th second). It should be VERY dark - it only contains read noise. Your master offset looks like its a properly exposed image.

What technique and settings are you using for capturing bias frames?


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Tonk
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Re: I am doing something very very wrong new [Re: srosenfraz]
      #6121275 - 10/06/13 08:46 PM

Quote:

First don't save your file from DSS instead make a copy of the autosave.tif and then use imagemagick to convert it to 16 bit. My understanding is that DSS has a bug in the 16bit save routine.




Can you supply a reference to this information? Can you say which specific versions of DSS?

I use DSS and the 16 bit save routine produces no faults for me.


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ICallHimGamblor
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Reged: 06/24/13

Re: I am doing something very very wrong new [Re: srosenfraz]
      #6121284 - 10/06/13 08:51 PM

Are you sure? I am looking at my bias frames, and they are all dark, and I look at the master offset in DSS and it is dark as dark can be.

As I recall, I took them at 1/2000 shutter speed with the lens cap on in my office, captured using BackyardEOS. I am not sure if somehow somewhere they got mixed up, but they look fine in the directory on my drive.


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Tonk
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Re: I am doing something very very wrong new [Re: Tonk]
      #6121287 - 10/06/13 08:53 PM

Quote:

I think I see the problem. Your "Master Offset" file doesn't look like its taken correctly. A Bias frame (or offset) is a frame that it taken for the least possible time with the camera covered (usually around 1/4000th second). It should be VERY dark - it only contains read noise. Your master offset looks like its a properly exposed image.




Yes that would certainly explain the outcome if the bias is actually not a true bias. As the "bias" data is subtracted from both the dark and light frames and if this is actually a longer exposure - this would kill most of the data!

Quote:

I am not sure if somehow somewhere they got mixed up,




This is an easy mistake to make if you point DSS at the wrong files while loading the bias images


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ICallHimGamblor
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Reged: 06/24/13

Re: I am doing something very very wrong new [Re: ICallHimGamblor]
      #6121301 - 10/06/13 09:00 PM

Here is a link to a screen shot of my master offset in DSS:

https://drive.google.com/#folders/0By0hG91nGRL9ckxUeXAxUXdTLTQ


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ICallHimGamblor
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Reged: 06/24/13

Re: I am doing something very very wrong new [Re: ICallHimGamblor]
      #6121315 - 10/06/13 09:06 PM

I am not adverse to the possibility that I have done something really silly here, but here is a link to screenshot the file list I saved in DSS, showing that the biases are listed as biases.

https://drive.google.com/#folders/0By0hG91nGRL9ckxUeXAxUXdTLTQ

EDIT: Actually, I would be willing to bet I've done something stupid... but I don't think that's it

Edited by ICallHimGamblor (10/06/13 09:30 PM)


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