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

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ICallHimGamblor
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Reged: 06/24/13

I am doing something very very wrong
      #6118829 - 10/05/13 11:01 AM

For some reason, I can't ever extract useful data from my stacked images. Last night, I took three hours of lights of Stephan's Quintet (60x180sec ISO400). I took 20 darks, I have 25 flats and 15 biases, and still can only raise the cluster just barely above the image floor. I have a two-hour stacked image of the fireworks galaxy (NGC 6946) that I can't raise above a wisp of a hint of an image.

I thought I was using StarTools improperly, but this is what Ivo said: "This is not really something that's a post-processing problem that ST can deal with. It seems like a stacking problem (incorrectly applied flats/darks/bias) or possibly an acquisition problem."

I am using a LP filter and am dithering using BackyardEOS + PHP.

Here is the stacked image: http://www.astrobin.com/58749/

And here is a random sub: http://www.astrobin.com/58912/

Can someone do an autopsy on this image to figure out what I am doing wrong?

Thanks.


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Chris_H
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Reged: 11/24/03

Loc: Norway
Re: I am doing something very very wrong new [Re: ICallHimGamblor]
      #6118875 - 10/05/13 11:28 AM

I think you are expecting too much at this focal length. You are also slightly out of focus which doesn't do you any good at all at this image scale (fine detail will be lost). Can't help you with startools though as I don't use it. But if it has levels and/or curves (and it should if it's made for astro!), I would play with them.

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mmalik
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Reged: 01/13/12

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Re: I am doing something very very wrong new [Re: ICallHimGamblor]
      #6118886 - 10/05/13 11:34 AM

If your sky allows, do 5 or 10min subs; raise the ISO to 800 or 1600. As a control test, do an ICNR in case you problem might be calibration. Use this... LPS filter if using something else. Get evals of ImagesPlus and PixInsight to stack and process, for comparison. Thx

Edited by mmalik (10/05/13 11:36 AM)


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srosenfraz
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Re: I am doing something very very wrong new [Re: mmalik]
      #6119064 - 10/05/13 01:39 PM

It looks like both your stacked image and your raw sub have had a stretch applied to them. It would be helpful to see the unstretched of each. Perhaps you could upload to someplace like Dropbox a raw sub (.CR2 file), as well as an unstretched 16 bit tiff?

You didn't mention what software you're using for stacking and calibrating. If you're using DSS, you'll want to save your final stack as a 16 bit tiff and be SURE that its not applying a screen stretch. You can tell if this is done correctly (unstretched), because the stacked tiff should be VERY dark (background 8 bit levels typically less than 5).

If you can post those two files, we'll probably have a better idea what you have happening.

Also, can you tell us more about ALL of the details about this image - what camera, is it modded, what scope (aperture and f/ratio), sky conditions (urban, rural, Bortle scale, Color zone, or SQM reading - some indication of how dark your sky is), what software you are using for stacking and calibration.


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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]
      #6119168 - 10/05/13 03:12 PM

Will an unmodded camera detect Stephan's Quintet? At mag 14.8 it seems like it would be down in the noise.

I also shoot with an unmodded camera. I am in a red zone (according to Dark Sky Finder) and have found that many DSOs barely scratch through the noise floor.


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srosenfraz
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Re: I am doing something very very wrong new [Re: ebacon]
      #6119177 - 10/05/13 03:18 PM

Modding a camera increases the red sensitivity and has little (or no effect) at the blue end of the spectrum. Most galaxies tend to be either blue or white/yellow in general color, so they usually respond well to unmodded cameras. You typically won't capture the Ha regions very well, but the majority of the galaxy is unaffected.

The galaxies in Stephan's Quintet are mostly blue and yellow, so one would expect an unmodded camera to work almost as well as a modded camera for a target like this.

Ojbects that are primarily Ha (very red) benefit significantly from modding the camera.


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TimN
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Reged: 04/20/08

Loc: Ontario, Canada
Re: I am doing something very very wrong new [Re: srosenfraz]
      #6119366 - 10/05/13 05:30 PM

I don't think there is enough data there. I agree with Mikes earlier comment - bump up the iso to 800 and try at least 5 minute subs.

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ICallHimGamblor
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Reged: 06/24/13

Re: I am doing something very very wrong new [Re: srosenfraz]
      #6119383 - 10/05/13 05:45 PM

Quote:

It looks like both your stacked image and your raw sub have had a stretch applied to them.




I have not stretched anything... those are the pics directly from the camera and DSS converted to JPG.

I am not sure what that tell you.


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ICallHimGamblor
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Reged: 06/24/13

Re: I am doing something very very wrong new [Re: mmalik]
      #6119389 - 10/05/13 05:49 PM

Quote:

If your sky allows, do 5 or 10min subs; raise the ISO to 800 or 1600.




I thought I read somewhere on here that subs should have a histogram that lies at 1/3 of the histogram graph. If I can go further than that, I would love to, but the histogram on the sub I posted looks right on that point. Let me know if I can go further...


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ICallHimGamblor
super member


Reged: 06/24/13

Re: I am doing something very very wrong new [Re: Chris_H]
      #6119392 - 10/05/13 05:50 PM

Quote:

I think you are expecting too much at this focal length.




Oh yeah... I am also using the standard celestron focal length reducer, so I am shooting at 6.something...


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Jamienite
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Reged: 11/30/11

Loc: Western Massachusetts
Re: I am doing something very very wrong new [Re: ICallHimGamblor]
      #6119409 - 10/05/13 06:02 PM

I agree with the above comments, 180 seconds is not enough for such a dim object. I've tried the quintet on a night where I wasn't tracking well and could only manage 2-3 minutes. I got results very similar to yours.

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Jamienite
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Reged: 11/30/11

Loc: Western Massachusetts
Re: I am doing something very very wrong new [Re: Jamienite]
      #6119420 - 10/05/13 06:09 PM

Oh, and bump up to iso800 for sure.

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shawnhar
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Re: I am doing something very very wrong new [Re: Jamienite]
      #6119445 - 10/05/13 06:29 PM

Restack the subs
In DSS, save picture to file, in the save options, make sure "Embed but DO Not apply" option is checked.
Upload that tiff to Dropbox or something we can download from
You might be surprised...


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srosenfraz
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Re: I am doing something very very wrong new [Re: ICallHimGamblor]
      #6119476 - 10/05/13 07:01 PM

Quote:

Quote:

It looks like both your stacked image and your raw sub have had a stretch applied to them.




I have not stretched anything... those are the pics directly from the camera and DSS converted to JPG.

I am not sure what that tell you.




I understand that you haven't consciously stretched anything - you probably have software doing it without you realizing it. From the camera, if you pull it into most software as a RAW, it'll apply a default stretch to it. When you save it as jpeg, it'll include that stretch. If you take it from the camera as a Jpeg, the camera will have applied the default stretch.

With DSS, the default behavior is to apply the screen stretch unless you tell it to save it as a 16 bit tiff and do NOT save the screen stretch with it. That's what it looks like you have there. Again, an unstretched image is usually VERY dark.

It would be quite valuable to see unstretched data, as you're asking about what you may be doing wrong to end up with less than optimal results. With unstretched data, we can look at it, process it, etc. to have a much better idea what the potential is.

With 3 hours of Stephan's Quintet, I would expect that you should normally have quite usable data. But, 3 hours is usually plenty enough time to have a good enough SNR to allow for a quality image - particularly at f/6.3. My image of Stephen's Quintet at f/6.3 on a C8 should be pretty comparable to yours. Mine was at ISO 1600, yours at ISO 400 - No big deal. If I had shot this at ISO 400, it would have looked more or less the same. I used 3 minute subs as well, and have a little over twice as much time. That means that my SNR is about 1.5x better than yours. That's better, but its not night and day either.

I suspect there's a decent image hidden in your data....

Edited by srosenfraz (10/05/13 07:06 PM)


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ICallHimGamblor
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Reged: 06/24/13

Re: I am doing something very very wrong new [Re: srosenfraz]
      #6119502 - 10/05/13 07:27 PM

Wow... I had no idea stretching was being applied to my image.

Here is the 'no adjustments' version.

http://www.astrobin.com/58959/


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srosenfraz
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Re: I am doing something very very wrong new [Re: ICallHimGamblor]
      #6119514 - 10/05/13 07:37 PM

That looks like the right stuff. The only thing is that we need that as a 16 bit tiff. I don't think you'll be able to post that large a file to Astrobin - that's why the suggestion to use something like Dropbox (free for up to 2 GB of total storage).

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Jamienite
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Reged: 11/30/11

Loc: Western Massachusetts
Re: I am doing something very very wrong new [Re: srosenfraz]
      #6119531 - 10/05/13 07:49 PM

Wow! I had now idea about this dss auto stretch. Thanks Scott. Also, looking at your Quintet image, I see that 3 minutes is plenty of exposure! Great image!

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ICallHimGamblor
super member


Reged: 06/24/13

Re: I am doing something very very wrong new [Re: Jamienite]
      #6119542 - 10/05/13 07:56 PM

Here is the TIF: https://docs.google.com/file/d/0By0hG91nGRL9aFZQVWlOSmJDakU/edit?usp=sharing

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srosenfraz
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Re: I am doing something very very wrong new [Re: Jamienite]
      #6119549 - 10/05/13 08:04 PM

Quote:

Wow! I had now idea about this dss auto stretch. Thanks Scott. Also, looking at your Quintet image, I see that 3 minutes is plenty of exposure! Great image!




Thank you very much. And you're welcome. Also, thanks to Shawn for the precise directions on how to save it correctly out of DSS.

One thing to note about the unstretched data - if you data is underexposed (i.e. ISO 400 with 3 minute subs from a dark sky), it can often be difficult to stretch this data using levels and curves (it can be done, its just very tricky). For these types of images, stretching with DDP (Digital Development Processing) tools makes all the difference in the world (as well as for well exposed images, too). For well exposed images (back of the camera histogram mountain well histogram well separated from left axis), stretching with levels and curves is the same as usual.


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mmalik
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Reged: 01/13/12

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Re: I am doing something very very wrong new [Re: ICallHimGamblor]
      #6119588 - 10/05/13 08:30 PM Attachment (23 downloads)

There seem to be calibration/gradient issues with your image. My go at your TIF below:

ImagesPlus:
1. RAW File Conversion (Skipped)
2. Align TSR/Combine/Crop (Only Crop)
3. Digital Development
4. Multi Point Flatten Background-Planar
5. Multiresolution Smooth/Sharpen
Saved as 16 bit TIFF for processing in PixInsight

PixInsight:
6. HDR Multiscale Transform
7. ACDNR (Noise Reduction)
Saved as 16 bit TIFF for processing in ImagesPlus/Photoshop

ImagesPlus/Photoshop:
8. Geometric Transform/Scale [0.3] (ImagesPlus [Skipped])
9. Smoothing & Noise Reduction (ImagesPlus)
10. ProDigital ‘Deep Space NR’ and HLVG (Photoshop)
11. Saturation (Block: 1 pass) and Noise Reduction (Photoshop)
12. Star Size & Halo Reduction, and Saturation (ImagesPlus)
13. Levels, Curves, Contrast, Brightness, Vibrance, and Color Balance (Photoshop)
Saved as JPG for posting


Processing instructions here...

Edited by mmalik (10/05/13 08:35 PM)


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