Resolved Saturation ADU in STX-16803

Discussion in 'STX and STXL' started by Lee Ho, May 12, 2020.

  1. Lee Ho

    Lee Ho Standard User

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    2 more images upload 110s, 120s
    I know the CCD's data express in 2^16=65535. But my CCD saturation level is about 46,000 ADU.
    Is there no problem?
    attatched Regulus captured image.
    attatched M67_110s(V), C/2017 T2_120s(R) images
     

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    Last edited: May 13, 2020
  2. Colin Haig

    Colin Haig Staff Member

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    That is a bit unusual.
    The FITS image shows an exposure time of 0.01 seconds.
    This is shorter than the mechanical shutter is guaranteed to work.
    The minimum exposure time for an STX-16803 is 0.1 seconds.
    Try again with a 0.1 second exposure.
     
  3. Mark Marfoglia

    Mark Marfoglia Cyanogen Customer

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    I have had this before where MAXIM values were not the same as PixInsight. My max values were around 46,000 as well. I never got to the bottom of the problem.

    Try inspecting it with another software.
     
  4. Colin Haig

    Colin Haig Staff Member

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    Mark, that doesn't make sense - FITS is FITS ;-)
    AstroImageJ 3.20 and NASA HEASARC fv 5.3 shows the same peak as MaxIm DL Pro 6.22 does, and all three agree with 45,735.
    If PixInsight is giving you something different, report it as a bug to them.
     
  5. Colin Haig

    Colin Haig Staff Member

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    Just wondering if @Bill might have some ideas regarding checking gain and offset calibration on the camera.
     
  6. Doug

    Doug Staff Member

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    What is your camera's serial number?

    There is no substrate adjustment on the KAF-16803 sensor, so you are in fact getting the sensor's full well depth. And there are more than enough bits in the converter to fully sample the noise floor at the current gain setting. So you are not losing any dynamic range or SNR performance. The STX-16803 oversamples the data somewhat.

    It is possible to adjust the gain and offset of the converter to make it saturate above 65,535. This actually reduces your well depth slightly. However, this will not gain you any extra performance compared to what you are getting now. We just try to make sure that the converter saturates at 65,535 so people don't complain!

    Personally, if I were setting up a camera optimally it would actually saturate at less than full converter range, to make sure the full well depth of the sensor was available. But customers don't understand that so we deliberately set up the cameras to saturate the converter.

    The A/D converter gain could be increased (and the Offset would have to be adjusted in tandem), so that the camera saturates at 65,535. If you really want it changed then a special procedure has to be done. We can arrange for that if you want to do it, but it isn't actually necessary.
     
  7. Lee Ho

    Lee Ho Standard User

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    serial number is X13110300
     

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  8. Doug

    Doug Staff Member

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    Test data for the camera looks normal.

    The camera is 7 years old. Has it always had the same saturation level?
     
  9. Lee Ho

    Lee Ho Standard User

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    Not always the same. Sometimes it was around 65535 and sometimes it was around 50000. most are 50000.
    As a teacher at Gyeonggi Science High School for Gifted, I came to this school this semester.
    I am teaching students astronomy.
    Please take a good look because it is intended to be used for students' classes and research.
    I heard Our school CCD was repaired twice around January 2019 and 2016.
     

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  10. Doug

    Doug Staff Member

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    I checked with @Bill. The last time the camera was returned it had the sensor replaced (original was sunburned apparently). So that would explain why the behavior is different from your 2017 image above.

    The camera's gain can be readjusted to increase the converter gain, so that the signal reaches 65535, if you like. We have a utility program for doing that, but it does require illuminating the sensor appropriately so we can determine the saturation point. @Adam Robichaud could help you with that if you wish to do this.
     
  11. Lee Ho

    Lee Ho Standard User

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    As I examined more data. Even before repairing the CCD, values of 50000 and 65535 appeared. The data I took over from 2016.
    The 2016 data also shows a value of 50000.
     

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  12. Doug

    Doug Staff Member

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    Your options are:
    1. Leave it as-is. There is no indication that you are losing any performance with the gain set where it is.
    2. Have our staff help you use the utility software to alter the converter gain/offset remotely.
    3. Return the camera for inspection.
    Please let us know how you would like to proceed.
     
  13. Doug

    Doug Staff Member

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    To close out this issue, Lee Ho selected Option 2, and Adam was able to remotely adjust the camera.
     

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