Staff Assigned: Adam Robichaud STXL-FW8G Image Test Request

Discussion in 'STX and STXL' started by Cliff Kotnik, Oct 25, 2017.

  1. Cliff Kotnik

    Cliff Kotnik Cyanogen Customer

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    I recently had to send my STXL-6303 back for repair and put a STXL-16200 on the scope in its place with the same FW8G. Since that time I have been struggling to get autoguiding going reliably. It is my impression that the guider CCD records much less signal than it did before. However, impressions can easily be wrong and I want to get some sort of quantitative test. The guider worked so easily with the 6303 that I never really got into this before.

    I was thinking something along the lines of this. Move the guider mirror as far toward the center of the scope FOV as possible. Point the scope at a flat panel. Taking images through the main 16200 CCD adjust the illumination so that a 10 sec (or suitable) exposure gives an average ADU of 30,000 in an area adjacent to the OAG mirror shadow. Then take an image through the guider CCD at the same exposure and measure the average ADU. Then the test criteria would specify some expected range outside of which I need to dig further into software, firmware or hardware issues.

    Is there something like this available from DL?

    thanks,
    Cliff
     
  2. Doug

    Doug Staff Member

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    It's not straightforward. The pixel size of a sensor acts a lot like f/ratio; bigger pixels get more light. Also the focal reducer in the guider assembly would affect it. Then there is the broadband QE difference between the two sensors. You can't use the peak numbers; you'd have to look at the whole QE graph.

    The procedure would be something like this:

    1. Determine the image scale for both the main camera and guide camera. You could use PinPoint for this. Calculate the ratio and take the square. That is the sensitivity of light flux on each pixel between the two sensors.
    2. Measure the ADU level for each camera using the same light source.
    3. Using the camera gains, convert ADU to photoelectrons for each camera.
    4. Adjust the numbers you get by the ratio calculated in step 1.
    5. Adjust the numbers you get by the ratio of the QE of each sensor.

    If you ignored Step 5 you could still get a ballpark number. If the difference is greater than a factor of two then something is probably wrong.
     
  3. Cliff Kotnik

    Cliff Kotnik Cyanogen Customer

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  4. Doug

    Doug Staff Member

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    In some cases it depends on binning mode. You will find EGAIN in the FITS header of your image.
     
  5. Cliff Kotnik

    Cliff Kotnik Cyanogen Customer

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    I ran this test with a constant light source over a range of exposure times. The test results are attached. The chart shows pretty clearly that the guider CCD has a serious problem at low light levels where most guide stars hang out. The data attachment shows the versions of software and firmware I used for this test.

    So it appears I need some ideas on how to determine if this is software, firmware or hardware.

    Thanks,
    Cliff
     

    Attached Files:

  6. Doug

    Doug Staff Member

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    Okay looks like the offset isn't set correctly. It might be possible to reset that remotely. Is it possible to set up a TeamViewer session? If so I'll get Adam or Tim to do that for you.
     
  7. Cliff Kotnik

    Cliff Kotnik Cyanogen Customer

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    >Is it possible to set up a TeamViewer session?
    The internet connect at the observatory does not permit that level of interactivity. Telephone capabilities are also unreliable there.

    So either I would need DIY instructions or I will need to remove the camera and filter wheel, bring them to my home and setup a TeamViewer session from here. Not knowing what is involved, I'll let you make the call on which way to proceed. Regarding timeframe, it will be Tues Nov 7th or Wed the 8th before I can do this.

    For my own edification, is the offset in the camera or the filter wheel? I ask since I did not have this problem when the filter wheel was attached to my STXL6303.

    Cliff
     
  8. Doug

    Doug Staff Member

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    It’s in the camera. Yes it would be best to do teamviewer. I’ll ask one of the guys to set it up with you.
     
  9. Cliff Kotnik

    Cliff Kotnik Cyanogen Customer

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    Andy,
    I'm ready.
    Cliff
     
  10. Cliff Kotnik

    Cliff Kotnik Cyanogen Customer

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    Adam,
    Attached is the screen capture of the CCD settings today,
    Cliff
     

    Attached Files:

  11. Cliff Kotnik

    Cliff Kotnik Cyanogen Customer

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    I reinstalled the camera at my observatory tonight. The images from the autoguider are dramatically better. Guiding is working fine. Thanks for the adjustment.
    Cliff
     

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