All-sky Camera - Image Filename Setting and Image Taking Frequency

Discussion in 'Specialty Cameras SG-4, AllSky, ST-I' started by Cheo Zi Wei, Jul 15, 2016.

  1. Cheo Zi Wei

    Cheo Zi Wei Standard User

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    Hi all,
    I have installed an all-sky camera 340 at my solar power plant.
    I have two questions:
    1. Can I save the image by setting the image filename as the time the camera takes the image?
    For example, 2016-07-15 14:15:20
    2. Can I set the camera to take a picture every 5 minutes instead of selecting the Baudrate given in the software of the camera?
    Thank you for your help!
    Regards,
    Zi Wei
     
  2. Alex Gibbs

    Alex Gibbs Standard User

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    Catalina Sky Survey, University of Arizona
    1. Not that I know of. I use a script to do this and save images to an archive.

    2. The "Exposure Interval" slider does this. The baud rate just determines the serial connection speed.
     
  3. Cheo Zi Wei

    Cheo Zi Wei Standard User

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    Hi Alex,
    Thanks for your reply.
    However, in the software, I can't find "Exposure Interval".
    Can you printscreen for me to have a look on this?
    I would like to have an image every 0 second as our real-time energy management system need to be very accurate in timing.
    Thank you.
    Regards,
    Zi Wei
     
  4. Alex Gibbs

    Alex Gibbs Standard User

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    Hi Zi Wei,

    Here you go:

    allsky.png

    Of course when set to "Continuous" the actual interval will be limited by your download time during the day. At the maximum 460800 baud that seems to be about 17 seconds. If you still want a 5 minute interval it can do that too.

    Alex
     
  5. Cheo Zi Wei

    Cheo Zi Wei Standard User

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    Hi Alex,
    Thank you for your reply.
    It seems pretty obvious get "Exposure Interval", sorry that I cant figure out why I didn't see that a few moment before ==
    I have one more question about this issue.
    What does the "Maximum Exposure Time" actually mean?
    Particularly, does "Exposure" means the action that the camera takes picture?
    Currently if I set the Exposure Interval to be continuous, and the Maximum Exposure Time will be 1 minute.
    Does that mean that the camera will take picture every minute?
    Thank you!
    Regards,
    Zi Wei
     
  6. Alex Gibbs

    Alex Gibbs Standard User

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    Hi Zi Wei,

    The exposure time is how long the camera is collecting light when taking each image. The software automatically adjusts it for the conditions. The
    "Maximum Exposure Time" is the longest time over which a single image is collecting light.

    During the day the automatic exposure time will be very short, much less than a second. In that case it doesn't matter what the "Maximum Exposure Time" is set to.

    On a very dark night the automatic exposure time can be well over 60 seconds. In that case setting "Maximum Exposure Time" to 1 minute will tell the software to stop collecting light after 60 seconds even if it would have done it longer.

    If you want to take an image every 5 minutes, day and night, set the "Exposure Interval" to 5 minutes. You can leave the "Maximum Exposure Time" all the way to the right unless you don't like how the night time images look.

    If you want to take images as often as possible then set the "Exposure Interval" to continuous and it will take images as fast as it can, which at night will be somewhere between every 17 seconds (at 406800 baud) and 1 minute.

    In summary: Always leave the baud rate at the fastest speed that works. Use "Exposure Interval" to set how often you want images. Use "Maximum Exposure Time" to control how images look at night.

    Alex
     
  7. Cheo Zi Wei

    Cheo Zi Wei Standard User

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    Hi Alex,
    Thank for your detailed explanation.
    We changed our plan to have an image every minute.
    So I think that means I will set to have the fastest baudrate, with the Exposure interval to be 1 minute, and Maximum Exposure Time to be all the way to the right.
    (We want image at night too).
    One last question:
    When I check the image properties, do you have any idea about the "date created"?
    Is the "date created" time that the image is taken, or the time that the image is successfully downloaded to my computer?
    Thank you!
    Regards,
    Zi Wei
     

    Attached Files:

  8. Alex Gibbs

    Alex Gibbs Standard User

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    Hi Zi Wei,

    The "date created" is when the file was created on the computer, which might be at the start or end of the download. I'm not sure. It doesn't exactly correspond to when the image was taken. Compare it to the time visible in the image to see the difference. There is another option for getting better times, but it is very complicated if you've never worked with FITS images before, so unless you really need it I would stick with using the created or modified time.

    The other option is save the FITS format images instead of the JPEG format. FITS has two benefits:

    1 - They aren't compressed so you can bring out more detail in some ways.
    2 - They contain the following information in a header:

    Header listing for HDU #1:
    SIMPLE = T
    BITPIX = 16
    NAXIS = 2
    NAXIS1 = 640
    NAXIS2 = 480
    INSTRUME= 'SBIG AllSky-340'
    DATE-OBS= '2015-10-10T23:59:58.720'
    BSCALE = +1.000000000000E+000
    BZERO = +3.276800000000E+004
    EXPTIME = +0.000000000000E+000
    CBLACK = 4769
    CWHITE = 56622
    END

    The DATE-OBS is what you might care about, but I'm not sure how precise it is either. Again, FITS images are MUCH more difficult to work with, and if you haven't used them before then I recommend sticking with JPEG. If you are curious about FITS images, you can tell the software to save FITS images under Setup -> Still Images. For more information on FITS files, see:

    http://fits.gsfc.nasa.gov/

    Alex
     

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