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Thread: Imaging light polluted vs dark site

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    Default Imaging light polluted vs dark site



    I'd like to hear your input on what to expect when imaging at sites with different levels of light pollution. Most of my limited attempts imaging have been at locations approximately level 5 on the Bortle scale (refer to location marked on light pollution map below).

    light location map.png

    Recently I had a chance viewing and imaging at a location approximately level 2 on the Bortle scale (marked on the light pollution map below).

    dark site map.jpg

    By naked eye viewing, the darker sight was spectacular. The view through an eyepiece was also amazing; much easier to identify galaxies and nebulae and make out details. I quickly spotted objects that I had previously failed to find at more light polluted locations. When it came to imaging, the contrast of objects such as M42 and M81 were much easier to see on the screen of a Canon T3i. As I captured frames I envisioned returning home with images that would stack and render a final image far superior to any I had collected previously. I was surprised to find that the final processed image from the dark location was almost indistinguishable from earlier work at more light polluted location.

    Below is a single frame of M81 galaxy captured at the more light polluted site (Bortle 5). It is a snapshot of the preview and histogram rendered using Canon's digital photo professional.

    12_21_17 M81 Frame and Histogram.jpg

    For comparison is the same type of preview of a single frame taken at the darker site (Bortle 2).

    12_23_17 M81 frame and histogram.jpg

    Stacking and processing images from each location yielded final images that looked nearly identical. The image below is actually a stack of images taken from multiple imaging sessions at both the lighter and darker imaging locations.



    My conclusion is that the M81 target is bright enough that there ended up being negligible difference in the final images. The differences might be more noticeable with dimmer targets or targets with features that are more difficult to tease out of the more light polluted skies. I'm also working on several aspects of the equipment to improve the imaging that may be limiting ability to resolve details and take better advantage of the darker sight.

    Is this similar or different to your experiences imaging at different levels of light pollution?
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    Default Re: Imaging light polluted vs dark site

    What is the exposure info on both shots? I'm guessing they are about the same. If that's the case then it explains why the Bortle 2 shot has such little data.

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    Default Re: Imaging light polluted vs dark site

    Nice work. Nothing beats a dark clear sky. Alway strive to get to the darkest locale possible when imaging and viewing. The main issue is a bit harder to process color images. The end results you post here have a green tint to them which is easily correctable in post. Look at HLVG filter. Works excellent.
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    Default Re: Imaging light polluted vs dark site

    Its when you shoot nebulas a dark site is better. Galaxys and starclusters is more brighter so its easier to image then a nebula. And in a dark site you can image much more faint stuff to.
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    Default Re: Imaging light polluted vs dark site

    Thanks for the feedback

    Quote Originally Posted by Lokifish View Post
    What is the exposure info on both shots? I'm guessing they are about the same. If that's the case then it explains why the Bortle 2 shot has such little data.
    Images were indeed 180 second exposures at both sites. As you can see with the histograms, I wasn't pushing the limits of exposure time at either site. Hopefully after mastering drift alignment and PHD2 settings I can push the exposure times up. I also believe focus was an issue that I will be addressing with a bhatinov mask. I think you may be right about more detail to be had in the fainter part of the dust lanes at the dark site if I pushed exposure time and addressed these other issues for resolving detail.

    Quote Originally Posted by Leveye View Post
    Nice work. Nothing beats a dark clear sky. Alway strive to get to the darkest locale possible when imaging and viewing. The main issue is a bit harder to process color images. The end results you post here have a green tint to them which is easily correctable in post. Look at HLVG filter. Works excellent.
    Thanks I will visit the HLVG filter and see what that renders.

    Quote Originally Posted by Micke187 View Post
    Its when you shoot nebulas a dark site is better. Galaxys and starclusters is more brighter so its easier to image then a nebula. And in a dark site you can image much more faint stuff to.
    This seems to match up with my limited experience so far, even though my initial expectations seeing views through the eyepiece and cursory look at higher contrast snapshots led me to expect more out of imaging results at the dark sight. I have now tempered expectations with the understanding that I would need to be equipped for longer exposure and sharp focus to take full advantage of the dark site for imaging purposes. For comparison of Nebula, I also captured some images of M42 nebula at the dark site (also 180 second frames). I don't have a an equivalent at the more light polluted site yet.
    Attachment 170942
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    Default Re: Imaging light polluted vs dark site

    Got you. You weren't shooting for equal SNR but simply used equal exposure times while tuning guiding. Not sure if you've seen this guide, but it really helped me set expectations, and calculate exposure and integration time under my Bortle 7/8 skies.

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