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Thread: Length of exposures

  1. #1
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    Question Length of exposures



    Hey, just a quick question. Are there any benefits of shooting 60 light frames with an exposure of 120 seconds instead of 120 light frames with an exposure of 60 seconds?

    I hope it makes sense, thanks.

    -Rasmus

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    Default Re: Length of exposures

    Quote Originally Posted by Rasmuscool99 View Post
    Hey, just a quick question. Are there any benefits of shooting 60 light frames with an exposure of 120 seconds instead of 120 light frames with an exposure of 60 seconds?

    I hope it makes sense, thanks.

    -Rasmus
    Hi Rasmus -

    In general longer exposures will provide better images when the images are stacked. The only reason not to use longer exposures would be if stars were starting to saturate.

    So, shooting 60 light frames with an exposure of 120 seconds will give better results than shooting 120 frames at 60 seconds.

    Steve
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    Default Re: Length of exposures

    It also depends on the camera. Some CCD cameras will not capture enough data with that short of exposure, while most CMOS cameras will.
    CCD cameras also benefit from longer exposures to over come the fixed noise. Where CMOS cameras are generally lower noise.
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    Default Re: Length of exposures

    You should always strive to make your exposures as long as possible. Unfortunately, there are quite a few obstacles that will prevent you from achieving long exposure times. Some of the obstacles are guiding errors, the seeing, your local level of LP, wind, battery life, etc. You need to experiment to see just how long you can make your exposure times so you can keep at least a certain percentage of your light frames. My personal limit is 80%, which means I'm willing to throw away 20% of my images for whatever reason makes them unsuitable. So whatever you set your "keeper" percentage at, if you can't attain this, then adjustments will be necessary.

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    Default Re: Length of exposures

    Longer exposures are not always necessarily better. It depends on upstream vs. downstream noise including digitization. Check the links in this message:

    Calculating Noise Sources (including LP) for a DSLR Camera
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