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  1. #1
    blaise's Avatar
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    Default Suggestions for Processing Please



    Hi guys:

    I am having difficulty getting real data out of some of my images. The procedure I follow is :

    Using Nebulosity, I normalize the images. I then stack them using default translation. I then take the result of the stacked image and go to work using Nebulosity's tools. First, I begin with a bit of offset correction, then I next move to levels/power stretching. At times, I will play with digital development. Howerver, the issue I am curretly having is that as I attempt to get rid of the brightness, I lose the data of the DSO in the process.

    Here are the particualrs for the included image (so that you can see what I am referring to as brightness). 2 minute exposures x 20. F1600 set at tungsten. I am also having the same problem with M42. As I attempt to darken the image, I am reducing the DSO.

    I have followed Stark's tutorial word for word in the manual. It works great with images at 30 seconds and even at 1 minute exposures, but the longer I expose, the more light I get in the image.

    I do not, however, use darks. The Canon takes a dark and includes it in the final image. This is where I could be going wrong. Is it?

    Any suggestions would be greatly appreciated.

    Thanks!
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    Default

    If your getting that in longer shots, than it seems to me that it may be light polution that is seeping into the sensor. I'm not to big into AP yet so this is all just speculation. I believe it is either that or, liek you said about not taking darks.

  4. #3
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    Default

    Quote Originally Posted by blaise View Post
    Hi guys:

    I am having difficulty getting real data out of some of my images. The procedure I follow is :

    Using Nebulosity, I normalize the images. I then stack them using default translation. I then take the result of the stacked image and go to work using Nebulosity's tools. First, I begin with a bit of offset correction, then I next move to levels/power stretching. At times, I will play with digital development. Howerver, the issue I am curretly having is that as I attempt to get rid of the brightness, I lose the data of the DSO in the process.

    Here are the particualrs for the included image (so that you can see what I am referring to as brightness). 2 minute exposures x 20. F1600 set at tungsten. I am also having the same problem with M42. As I attempt to darken the image, I am reducing the DSO.

    I have followed Stark's tutorial word for word in the manual. It works great with images at 30 seconds and even at 1 minute exposures, but the longer I expose, the more light I get in the image.

    I do not, however, use darks. The Canon takes a dark and includes it in the final image. This is where I could be going wrong. Is it?

    Any suggestions would be greatly appreciated.

    Thanks!
    Some feedback:

    - your ISO (I'm assuming this is the F1600 number you're providing, i.e. ISO1600) is two to four times what it needs to be for a two-minute exposure. Depending on the ambient temperature, you should probably be using ISO400 to ISO800.

    - try daylight white balance vs. tungsten - this is actually a better starting point

    - are you shooting RAW, or JPEG? Sounds like JPEG if you're using in-camera noise reduction. Shoot RAW+JPEG, process the RAW frames, and save the JPEG's for diagnostic help.

    - in-camera noise reduction does an inferior job, and takes longer per-exposure than shooting dark frames. My suggestion would be to shoot three to four dark frames in the image sequence - one at the beginning, either first or second frame, two in the middle of the sequence, and one as the final frame. For a 2 x 20 stack, try the following sequence:

    L D L L L L D L L L L L D L L L L L D L L L L L D

    Where "L" is a light, or image frame, and "D" is a dark frame. Allow the sensor to "rest" for 1 minute between each exposure - this will reduce the thermal and read noise. Using 2-minute exposure duration, this results in a 71-minute image session.
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  6. #4
    blaise's Avatar
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    Default

    Thanks Austin. I did mean ISO 1600. I will try 800/400 next time. I'll give the darks a shot as well.

    Thanks again.

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    Default

    That is definitely light pollution you have there, particularly as the longer you expose, the worse it gets.
    What you need is an EOS type clip filter, which is made for a Canon, for example an Astronomik EOS CCD CLS clip filter. I believe that Hutech do one as well, along with Baader, Orion, Lumicon, etc. Using one of these, it will allow your exposures to get up towards 15-20 minutes, depending on your local sky conditions, however, depending on your particular camera, 10-15 minutes is probably your max. Also, follow Austin's advice for ISO, settings, etc.
    Last edited by TheDecepticon; 02-22-2010 at 04:29 AM.

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  9. #6
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    Default

    A few things which may assist you with DSLR imaging.
    1 You definitely need to take and calibrate the image with Flat frames. This will even out the illumination across the CCD and remove the vignetting you seem to have.
    2. You need to image with a lower ISO. I always used ISO 800 with my 40D and never changed to 1600 because it either over saturated images or increased the noise until it blocks the image out totally.
    3. Light pollution can also cause problems but at 2 minutes shouldn't be too much of a problem. An LP filter might help.
    4. Get your focus spot on and you will bring out the best in your images.
    5. Take lots of exposures (at ISO800 and 2 minute exposures aim for about 2 hrs worth) you then have enough signal to pop out above the inherent noise.
    6. try some bright targets and practice your processing and capture on them until you work out how to beat the noise, light pollution and illumination problems you seem to be having.
    7. Leave the white balance on auto. Any colour balance issues can be processed out later.

    Good luck
    Cheers
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  11. #7
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    Default

    Blaise,

    Thanks for the posting. The responses you got were also very valuable bits of information for me too.
    SXINIAS

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  12. #8
    blaise's Avatar
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    Thanks guys. Don't know what I would do without this forum.

  13. #9
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    Default

    blaise;]Thanks guys. Don't know what I would do without this forum.
    I agree with you here.
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    Default

    Blaise I hope you don't consider this a hijack as you know we are both having the same problems.

    I'm actually imaging m35 as we speak. I just learned what dark frames are and am adding them to my frames, but what are flat frames?

    Finally what about shooting at lower iso's? I'm currently trying at iso 200. Thanks
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