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Thread: M51.... needs more data.....

  1. #1
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    Default M51.... needs more data.....



    Hello all.

    Well, I added my darks flats and bias files to the lights of M51 that I shot last night. I have come to the inescapable conclusion that it needs a whole lot more data to increase the signal to noise ratio. This image is a prime example of low signal to noise ratio.(the noise is so prevalent it looks like its been sand blasted!) On the plus side my focus seems pretty good. Hopefully it will be clear again to and I can collect more data.

    Located "In the heart of the light bulb".

    C8 @ f-6.3 (focal reducer)
    Canon EOS XSI (unmodded) @ ISO 800 11x8min subs with an Astronomik CLS clip light pollution filter.
    Captured with Backyard EOS
    Guided with PHD Guiding (QHY Kwik Guider)
    Stacked in DSS, and bashed about in PixInsight

    m51-2b.jpg
    Last edited by DrGui; 05-19-2015 at 05:02 PM.
    -John
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    Default Re: M51.... needs more data.....

    Good luck with more clear nights to add some data.

    Sandblasted? maybe a 600 grit sandpaper?
    I am sure it will improve with the additional data.

    Cheers
    .

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    Default Re: M51.... needs more data.....

    What about dropping the exposure down to 4Min or 2, noise could be from the sensor heating up. Your camera is from 2008 if I recall, when I used my Oly E-510, I could see the images go very grainy as the night progressed and that was for 60sec exposures, all of those frames I could not use near the end.
    Neil
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    Default Re: M51.... needs more data.....

    You have excellent data to work with. There is a lot of chrominance noise, however, this is mostly limited to the background sky.

    I recommend that you review some of the techniques used by others in processing their photos or especially those in the Challenge contests. This is not unusual to deal with and should be pretty straightforward with the data you already have. Using a false flat, you can use a "color burn" combination routine in PS that when the transparency is adjusted, will equalize a lot of the background sky. Study the histogram as well. The red channel would likely benefit tremendously from applying a "S-curve" to it.

    Once the RGB channels are basically equalized for the background sky and reduced to 20,20,20 or somewhat lower using the color burn technique, I will set the grey point using the curves or levels dialog at this point.

    I then export the files as a full size .tiff and process the image in Noise Ninja. (For the noisiest frames, I will split the files and process each separately.)

    I recommend shorter exposures without using a filter or possibly using a Orion Sky Glow or nearly clear filter. Galaxies are basically full spectrum sources and take longer with filters. Considering the LP, limit your frames to 25 to 50% of your full histogram setting. The lower value is better. You can also perform a software binning routine using certain programs such as Nebulosity that will improve your SNG quickly, especially if the seeing conditions were not in-line with your sensor's small pixel size.
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    Default Re: M51.... needs more data.....

    Thanks John!
    You've given me quite a bit to chew on!
    -John
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    Default Re: M51.... needs more data.....

    Your welcome!

    M51 is one of my favorite targets and I took some frames of it last week that I still need to develop.

    One of the first that I took last year is shown below. The total integration time was likely <15 minutes. Of note is the background sky...
    The Eagle's Nest - Bortle 4-5 sky - scopes: Celestron C8 SCT w/MOTOFOCUS; ES ED102 APO CF MoonLite w/auto focus! FR/FF(s): Starizona SCT Corrector; Stellarvue 0.8 FR/FF; Explore Scientific 1.0 FF Filters: 1.25 inch - Orion Ha (1.25in), 2 inch - UHC, polarizer, Orion Sky Glow, Astronomik CLS-CCD Mount: Celestron AVX Cameras: Canon 60d (modded); Atik 383L+ OSC Guiding: Olivon OAG; ZWO ASI120MM; QHY QHY5-II Mono

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    Default Re: M51.... needs more data.....

    I agree that you may be able to do better without getting piles and piles of additional data.

    I took this unguided as about 40 90-second light frames and 1-2 darks (no flats or bias frames) for about 60 minutes of total time: http://www.tourdegiro.com/personal/m51-5.jpg. I was about 20km outside Kitchener-Waterloo, beside a bunch of ridiculously-bright streetlights at a friend's house.

    My equipment:
    8" newtonian (f5.0)
    Canon T2i (EOS 550D)
    40x90sec @ ISO 1600

    Interesting to read about sensors heating up in this thread. Once I get the autoguider up and running I'll have a new thing to worry about I guess.

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    Default Re: M51.... needs more data.....

    I agree that you may be able to do better without getting piles and piles of additional data.

    I took this unguided as about 40 90-second light frames and 1-2 darks (no flats or bias frames) for about 60 minutes of total time: http://www.tourdegiro.com/personal/m51-5.jpg. I was about 20km outside Kitchener-Waterloo, beside a bunch of ridiculously-bright streetlights at a friend's house.

    My equipment:
    8" newtonian (f5.0)
    Canon T2i (EOS 550D)
    40x90sec @ ISO 1600

    Interesting to read about sensors heating up in this thread. Once I get the autoguider and can take shots beyond 90 seconds I'll have a new thing to worry about I guess.

 

 

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