STT-3200ME Bias image issue

Discussion in 'STT Series (obsolete)' started by Mark Blackford, Mar 8, 2017.

  1. Mark Blackford

    Mark Blackford Cyanogen Customer

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    Hi All,

    bias images recorded with my new STT-3200ME have an obvious brightening on the left side, see screen capture below. The graph show a linescan across the master bias frame which was made from 127 individual bias frames recorded in a darkened room with lens cap on.

    upload_2017-3-8_21-39-28.png

    I expect to see a uniform ADU level across bias images with random noise superimposed. What would cause this brightening in my bias frames? Cheers,

    Mark
     

    Attached Files:

  2. Colin Haig

    Colin Haig Staff Member

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    Mark - I'm just another customer, but to me it looks like a small variance in the noise - maybe 6-10 ADUs. Tough to tell how much from the above. Could you upload a FITS file so people could take a look?
    Did you use a plastic cap? Some IR may be getting through - try something metal, or point the camera nose-down on a wooden desk..
     
  3. Doug

    Doug Staff Member

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    Yes please post a single unmodified FITS file, bias frame, taken at temperature and with the camera in the dark. Scattered light can get around the shutter to some extent if the camera is not in the dark.

    Also please be aware that a small background variation is normal for some models, and isn't a problem as long as it is consistent.
     
  4. Mark Blackford

    Mark Blackford Cyanogen Customer

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    Hi Doug and Colin,
    thanks for your quick responses. Attached is a single bias frame as requested. The camera was attached to a Canon 200mm f2.8L lens which was capped (plastic) and the lens butted up against a wall to reduce any incident light entering through the lens. Room lights were out during acquisition but the laptop screen did cast a little light. Cheers,
    Mark
     

    Attached Files:

  5. Doug

    Doug Staff Member

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    Yes I can see a bit of a "wave" in the image. I've checked the bias frames for several STT-3200 cameras from our production records. That "wave" is characteristic of the STT-3200 model. It precisely repeats so it 100% subtracts out.

    FYI we have a minor firmware update for the STT-3200. It slightly tweaks the horizontal timing on the sensor clocks. It won't change your "wave", but it will actually reduce your noise floor slightly! I believe Adam hasn't uploaded it yet, so I just passed him a message to remind him to do so.
     
  6. Mark Blackford

    Mark Blackford Cyanogen Customer

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    Thanks Doug,
    If this is typical for the STT-3200 then master frames should compensate effectively. I'm about to make another master bias to see how it compares with the first. I'm sure I'll have a bunch of other questions as I learn how to use this camera.
    By the way, the link to the "How To Update Firmware" sticky in this forum does not work. Cheers,
    Mark
     
  7. Mark Blackford

    Mark Blackford Cyanogen Customer

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    Hi Doug,
    now my bias frames have average pixel values of about 6500ADU, whereas yesterday they were about 1450ADU. One bias frame from tonight is attached. This behavior can't be normal. What do you think is going on? Cheers,
    Mark
     

    Attached Files:

  8. Doug

    Doug Staff Member

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    The new Version 2.64 STT firmware was just released. It tweaks the horizontal clock timing, resulting in slightly better noise performance.

    The upgrade is recommended for STT-3200 users only (it has no effect on other STT models).
     
  9. Mark Blackford

    Mark Blackford Cyanogen Customer

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    Hi Doug,

    in my last post above I reported that my bias frames had unusually large pixel ADU values. However that only happened on the one night, since then bias frames have median pixel values consistently within 1 or 2 ADU of 1240 ADU.

    I have no idea why that one night was different. I updated the STT-3200ME firmware as you recommended, but that was after bias frames returned to normal. Cheers,

    Mark
     
  10. Doug

    Doug Staff Member

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    It sounds like when your camera powered up it failed to properly initialize the A/D converter for some reason. Hopefully it was just a one-time glitch caused by unstable power or something.

    If it ever happens again, try cycling power to clear it... and also let us know.
     
  11. Mark Blackford

    Mark Blackford Cyanogen Customer

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    Thanks Doug,
     

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