New STF8300m Board

Discussion in 'STF Series' started by Kenn Hopkins, Jan 14, 2020.

  1. Kenn Hopkins

    Kenn Hopkins Standard User

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    Repaired my STF8300m by replacing the board, SBIG Repair performed the repair, and now I'm no longer able to image the Moon. I used to be able to use the HA filter and an exposure setting of 0.01 to obtain a good gray scale of the Moon. With the new board I'm no longer able to get a good gray scale of the moon, it is blown out with the Moon being over exposed. When I received the camera back I updated the Fireware, but not sure if that caused it or not. In CCDOps I'm only about to set the exposure to 0.09 no longer to 0.01.

    Suggestions?
    Kenn
     
  2. Doug

    Doug Staff Member

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    The STF-8300 has never been capable of exposures below 0.1 second. The shutter can't move that fast.

    I've done HA moon exposures before with a different model of camera, and it was still pretty close to the camera's saturation point. It's possible there's a slight difference in gain between the two boards.

    Do you have another narrowband filter you can try?
     
  3. Kenn Hopkins

    Kenn Hopkins Standard User

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    Attached are two images. the first one is prior to the 'Repaired' STF8300m using a Astrodon Gen II HA filter, FLT132mm scope, and an exposure setting of 0.01. The other image is using the same equipment or with the 'Repaired' STF8300m.
    There is a large difference. I really like my camera, but it looks like something has defiantly changed.
    Kenn
     

    Attached Files:

  4. Doug

    Doug Staff Member

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    It's impossible to tell anything from a JPG image; please upload original FITS.
     
  5. Kenn Hopkins

    Kenn Hopkins Standard User

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    Attached are two images of the moon. I'm sure you will be able to tell which one has the 'Repaired' circuit board in it.
    Same STF8300m with Astrodon Gen II HA filter, 0.01 set exposure in the data acquisition program Astro Photography Tool(APT) but one has the old board in it and the other has a 'Repaired' board.

    Appreciate your time spent on this issue.
    Kenn
     

    Attached Files:

  6. Doug

    Doug Staff Member

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    I have a few thoughts:
    1. Looking at the same feature on the moon, I'd estimate the "new" image is 53% brighter.
    2. The gain of the camera with the new board appears to be slightly higher. That is adjusted when the camera is tested to optimize full well depth etc. Based on the standard deviation of the background in the corner of the image the gain is perhaps 15% higher. That brings the ratio down to 33% brighter.
    3. The old moon photo is taken at a different lunar distance; it appears about 5% smaller. That means it is actually fainter due to inverse square law; roughly 10% less. That brings the ratio down to 20%.
    4. There are also possible atmospheric extinction differences depending on the altitude of the moon during the two images
    5. Unlike the new photo, the old old moon photo wasn't at full moon; there is a significant phase defect.
    It's hard to do a proper apples-to-apples comparison without lab equipment.

    The camera seems to be working very well.
     
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  7. Colin Haig

    Colin Haig Staff Member

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    Kenn - I'll let @Doug comment on whether there is anything we can do to make the camera less sensitive, but thought I'd offer my 2 cents.

    It seems a bit odd that a camera that can see more faintly is a bad thing... but I can understand if all you do is moon shots, that this is a big deal for you.
    The fix I would use is a neutral density filter or an aperture mask on the front of the scope.

    You're shooting the second brightest object in the sky with about 900mm of focal length at f/7.
    The new image is of a nearly full moon, vs a not-yet-full a few days earlier.
    If I was using a DSLR, I'd cut the exposure by about 50% from gibbous to the full moon.
    The STF has a fastest shutter time of 0.1 seconds, 1/10th. Normally I shoot a DSLR at about 1/250th to 1/400th for a full moon.
    Am surprised APT lets you set the shutter speed faster than what the camera is rated for.

    APT is up to 3.82 and fixes some bugs. Not sure if they address this issue.
     
  8. Kenn Hopkins

    Kenn Hopkins Standard User

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    Doug and Colin, I understand what you both are saying. When the moon is out I take images of it just for the fun of shooting the moon, and I have a lot of them. And yes the DSO objects 'seem' to have a bit more brightness in them as compared to the same object I took last year. I'm not complaining about the 'Repaired' camera I'm just curious what could to changed between the old and new boards. I know some would say I have enough images of the moon to last a life time but a few more could not hurt.

    Thank you both for taking the time to look at and explain what could be the cause of the brighter moon images.
    Kenn
     

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