Bright corner of first exposure

Discussion in 'STX and STXL' started by VictoriaSaucier, Oct 25, 2019.

  1. VictoriaSaucier

    VictoriaSaucier Cyanogen Customer

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    I've been having a problem with the first long (several minutes+) exposure every evening and I'm hoping there's some setting I can change to fix it. The image below can better describe the problem than I can in words. It happens with both darks and lights, but subsequent long exposures do not have the noise in the corner that the first one does. I have not determined the duration before the noise reappears. It's pretty faint, the pixels in the corner being about 100 points higher than they should be, but it's obviously undesirable.

    This noise even happens on the first long exposure even if I have taken several shorter exposures before-hand.

    I am not using RBI pre-flash.

    The camera is an STX-16803.

    I am guessing some noise from the camera itself that builds up, but it's not like ghosting from a really bright star. I don't know why the short exposures don't "clear it out".

    Any thoughts?

    Thanks!
    -Tori

    Edit to add: Running latest drivers/firmware, and MaxIm 6.20
    sbigudrv.dll 4.99 build 7
    sbigu64.sys 2.41.0.1338
    sbigpcam.hex 2.46
    sbiglcam.hex 2.20
    sbigfcam.hex 2.25
    sbigfga.bin 2004.11.10

    stxusb.bf2 1.06
    stxga.bf2 2.54
    stx16803.bf2 1.00.05
    stx0340.bf2 1.00.04
     

    Attached Files:

  2. Doug

    Doug Staff Member

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    That looks rather like amplifier glow.

    There is a transistor readout amplifier in the top left corner of the CCD array. That's where all the pixels clock out. All semiconductors behave a little bit like LEDs - when they have power going through them, the glow a bit. That's where amp glow comes from.

    To prevent that from showing up on the image, we turn the power supply voltage down on that amplifier during integration. Then just before we read out the sensor, we turn it up again.

    I'm thinking maybe there's an obscure firmware bug in there somewhere, that is sometimes leaving it powered up. I'll ask our firmware engineer to have a look at it. We're right in the middle of a big project so it might take a few days.
     
  3. VictoriaSaucier

    VictoriaSaucier Cyanogen Customer

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    Thanks for the quick reply Doug! I look forward to hearing back when your guy has time!
     
  4. Mark de Regt

    Mark de Regt Standard User

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    FWIW, I have a very similar issue with my STX-16803--amp glow in the upper left corner on some (but not all) light-frame images. There does not seem to be a pattern (will happen in three or four consecutive images, then not for a number of images; then happen again).

    When I posted on the SBIG email group in June, it was clear that it's a very common issue with this camera. It was suggested that "There is choice in the firmware to turn on the amp only when reading out data. The only place to access that choice I know of is in CCDops, the SBIG camera control software. To find the switch: Open CCDops; Camera menu > STX/STT; Customer options; Check the box “Vdd Normally Off”.

    This may have reduced the frequency, but it certainly did not eliminate the problem.
     
  5. VictoriaSaucier

    VictoriaSaucier Cyanogen Customer

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    Thanks Mark - I'll look for that setting. I've since seen on other forums that this is a pretty common problem. I'm sorry to hear it's not just me and that it's a lingering problem!
     
  6. Doug

    Doug Staff Member

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    I've not been able to replicate this problem in my observatory, nor has the engineer assigned to this been able to replicate it on the bench.

    Please make sure your drivers and firmware are fully up-to-date. Download the latest version of SBIG Driver Checker (be sure to use the improved version of the program, don't just use the Update button), available at:

    ftp://ftp.sbig.com/pub/SetupDriverChecker64.exe
     
  7. Mark de Regt

    Mark de Regt Standard User

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    Thanks, Doug.

    My camera did this from brand new, in May of this year, and it really is a problem widely experienced. I'd download the latest version of the driver checker, but it demands a login that I don't have. Any ideas?

    Edit: I found a portal that allowed me to download the driver checker without a login. All drivers were up to date, except sbigu64.sys was dated 1/13/09, and has been replaced with one dated 1/27/15. Could this be related?

    Anyway, I'll report back next time I image.

    Mark
     
    Last edited: Oct 28, 2019
  8. VictoriaSaucier

    VictoriaSaucier Cyanogen Customer

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    I changed enabled the Vdd normally off switch and created a few darks - so far the glow is *not* on my images. If it recurs I'll check drivers.

    Doug, can you confirm there is no harm with that switch?

    Thanks guys!
     
  9. Doug

    Doug Staff Member

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    Try again. Was a temporary web site issue.
     
  10. Doug

    Doug Staff Member

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    Switch doesn’t hurt anything. It just turns down the amplifier voltage between exposures, not just during. (It turns back on for the readout.).

    Doesn’t really appear to do anything useful; I don’t know why it was added.
     
  11. Mark de Regt

    Mark de Regt Standard User

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    I'm the second one to post about this problem, above.

    As I said above, I updated my drivers as Doug suggested; one was out of date. I was fortunate enough to get 24 images last night; none had the amp glow (several had brightness all along the left margin, but that's presumably a separate issue). So perhaps that took care of the issue for me.

    I'll post again if the amp glow crops up again.
     

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