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Comparison of Background Intensity Between Calibration and Light Frames

JimS
in General
Hi,

I am a new member to the Forum and have been working my way through Adam's FastTrack tutorial videos. There was a video (I believe the second or third) on examining single frames from the light and calibration frames using the "readout" function as a screening technique that could alert one to potential problems down the road with processing the images in Pixinsight.

The data supplied in the tutorial had K values of about 0.012 for the light frames and 0.007 for the dark frames (ASI2600MC Pro, Gain = 100, T=-10C, 120 sec). My data that I recently collected from Bortle 5 skies was 0.012 for light and 0.01 for dark frames (ASI183MC Pro, Gain=120, T=-10C, 120 sec). The relative difference between the background intensity for my two calibration frames is tiny. Is that to be expected for an entry level camera such as the ASI183?

Thanks,
Jim

Comments

  • BlockHeadBlockHead
    It depends, is the answer. It could be perfectly normal.
    But I also wonder...are you certain you told me everything?
    (e.g. Are you using any filter?? as is so commonly done)

    -the Blockhead
  • JimS
    Darn,
    I tried to be complete, but you are absolutely correct! I have omitted some information. The optical train included a 2" L-eXtreme dual-band filter with a SpaceCat51.

    Jim
  • BlockHeadBlockHead
    Yes... and THAT explains everything. I knew it.. but I did not want to assume. 
    When you are using narrowband filters the sky will be very dark. So that indeed you will not see a large difference between your dark frame and your light frame. 

    Please search for "Pedestal" on my site. You must now watch that video (and report back here that you found it). It is in the section on the WBPP materials. You need to make certain you understand whether you need a pedestal.

    -the Blockhead
  • JimS
    Wow. Absolutely eye-opening and a really helpful video. Thanks.

    I found the video, WBPP: Pedestals for NarrowBand imagery, and watched it twice. My calibrated images were definitely suffering from oversubtraction from the master dark frame and clearly indicated a need for a pedestal.

    I ran WBPP twice; first with zero pedestal and then with a pedestal value of 100. I used your PixelMath script to highlight in red the pixels with a value of zero or less from a single calibrated light frame. I have attached my results to this post.
    docx
    docx
    Pedestal_Comparison.docx
    3M
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