STF CCD, FW8 and OAG 8300 Backfocus Validation

Discussion in 'STF Series CCD Cameras' started by Darren Wesemann, Oct 4, 2021.

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  1. Darren Wesemann

    Darren Wesemann Cyanogen Customer

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    The panel is evenly eliminated, but just in case I did the experiment suggested, and the shadow stands still regardless of the orientation of the lit panel. I attached another flat and a few pics, one showing the CCD with the filter wheel and pickoff mirror, one showing the lit panel up through the optical tube from the perspective of where the CCD attaches, and the other showing the whole setup with the lit panel resting atop the ota. Also, I ran the flat exposure process in MaximDL with the CCD dethatched so I could watch the filter wheel move to ensure it wasn't stopping incorrectly, and it moves and stops as it should, ending in the right place. The shadow is still there, so I'm at a loss as to what would be casting it. Any other ideas?
     

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    Darren Wesemann, Oct 19, 2021
    #21
  2. Doug

    Doug Staff Member

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    Maybe we're actually seeing some kind of reflection, not a shadow?

    Did you try Colin's suggestion of rotating the camera/wheel/guider assembly in the focuser? If the pattern doesn't rotate then it's something in the camera equipment. If it does then it's in front.

    Here's something else you could try: remove the OAG-8300 completely. If the shadow goes away then we'll be sure it really is the OAG that is causing it.

    Also, can you take a photo into the camera with the shutter open?
     
    Doug, Oct 19, 2021
    #22
  3. Darren Wesemann

    Darren Wesemann Cyanogen Customer

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    Right, sorry, forgot to mention, no different in the orientation of the camera assembly, attached is both the 45 and 90 degree orientation...
     

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    Darren Wesemann, Oct 19, 2021
    #23
  4. Darren Wesemann

    Darren Wesemann Cyanogen Customer

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    Here's a pic with the shutter open...
     

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    Darren Wesemann, Oct 19, 2021
    #24
  5. Doug

    Doug Staff Member

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    Hard to tell from the shot, but the mirror assembly still looks close to the chip. The telescope does have an f/ratio, which means the beam comes in at an angle. (What is your f/ratio by the way?)
     
    Doug, Oct 19, 2021
    #25
  6. Darren Wesemann

    Darren Wesemann Cyanogen Customer

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    f/11
     
    Darren Wesemann, Oct 19, 2021
    #26
  7. Colin Haig

    Colin Haig Staff Member

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    I think it's a C14 Edge HD at f/11. Unless there's a reducer in there (that I don't see in the photo).
     
    Colin Haig, Oct 19, 2021
    #27
  8. Doug

    Doug Staff Member

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    Even at f/11 the beam goes out about a tenth of an inch for every inch from the focal plane.
     
    Doug, Oct 19, 2021
    #28
  9. Darren Wesemann

    Darren Wesemann Cyanogen Customer

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    Regarding the f/11 beam, with the pickoff mirror back as far as it can go, I still get the shadow. The file "Flat-STF-Out-Full.fit" is the flat with the pickoff all the way back, and the "Flat-STF-Out-1.fit" is slightly forward. Note the shadow appears to be in the same place regardless of where the pickoff mirror. I attached the view from the ST-i for reference in both positions, in case that provides any clues.
     

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    Darren Wesemann, Oct 20, 2021
    #29
  10. Doug

    Doug Staff Member

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    You can subtract "Flat-STF-Out-Full.fit" and "Flat-STF-Out-1.fit", and the result is nearly flat. That rather suggests the pattern isn't due to the pick-off mirror.

    Try removing the OAG from the stack, and see what you get.
     
    Doug, Oct 20, 2021
    #30
  11. Darren Wesemann

    Darren Wesemann Cyanogen Customer

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    Attached are flats with the OAG removed, and then with the Filter Wheel also removed. The shadow appears to be there with just the STF. I've included some additional pics of the CCD chip, and the other parts if it's useful... so what does this mean? (my STF has been sitting in the box unopened for a few years until I found time to devote to setting everything up... so whatever it is, it's been there from the beginning). Let me know your thoughts. Thanks!
     

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    Darren Wesemann, Oct 21, 2021
    #31
  12. Doug

    Doug Staff Member

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    For a starter, it means we're chasing a red herring. The OAG and filter wheel aren't causing anything.

    If you rotate the camera, I assume the pattern stays as-is?

    Have you inspected the front of the camera's chamber window for smudges?

    Have you tried recharging the desiccant?
     
    Doug, Oct 21, 2021
    #32
  13. Darren Wesemann

    Darren Wesemann Cyanogen Customer

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    Rotating the camera doesn't change the shadow. The front of the camera's chamber is clean, no smudges. How do I recharge the desiccant?
     
    Darren Wesemann, Oct 21, 2021
    #33
  14. Doug

    Doug Staff Member

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    Doug, Oct 21, 2021
    #34
  15. Darren Wesemann

    Darren Wesemann Cyanogen Customer

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    I recharged the desiccant, plugged it back in, and let it sit for two days before trying again... Attached is the flat I just took, shadow is unchanged.
     

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    Darren Wesemann, Oct 24, 2021
    #35
  16. Doug

    Doug Staff Member

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    Well... the variation is about 5%. I'm not sure what the cause is, but it appears consistent and should flat-field out. One option is to simply accept it and continue.

    Another option is to send your camera in, but all we could really do is try cleaning it to see if that improves things.

    What is your camera serial number?
     
    Doug, Oct 24, 2021
    #36
  17. Darren Wesemann

    Darren Wesemann Cyanogen Customer

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    Where can I find the serial number?

    Back to the original issue though, the focus problem, assuming the 5% variation isn't causing an issue with focus, I shot three examples and tried auto focus on all three, Polaris, Jupiter and one of J's moons... All three are attached with screenshots of the autofocus after each. Let me know what I'm doing wrong, or is there a different issue?
     

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    Darren Wesemann, Nov 3, 2021
    #37
  18. Doug

    Doug Staff Member

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    There's a label on the side.
     
    Doug, Nov 3, 2021
    #38
  19. Darren Wesemann

    Darren Wesemann Cyanogen Customer

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    Serial: 83F011187
     
    Darren Wesemann, Nov 3, 2021
    #39
  20. Doug

    Doug Staff Member

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    Oh, that's a 2014 model. Back then SBIG didn't keep sample images for manufactured cameras, so I don't have a comparison.
     
    Doug, Nov 4, 2021
    #40
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