STX-16803: dark edge on my dark frames

Discussion in 'STX and STXL Series Cameras' started by NickA, Jun 26, 2021.

  1. NickA

    NickA Standard User

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    Hello, I'm re-shooting my darks & bias library and (once again) I noticed a dark edge running down one side of my images. I did adjust the internal guide chip, but there was no noticeable affect on the images. (Note: I'm imaging unguided at the moment, without the STXGuider & AO-X, just the STX and FW7.)

    Previously I've ignored this dark edge, but now I'm curious as to whether this is an issue, and/or how I should address. See FITS file linked below. I've also attached an "analysis" image that I generated using a PixInsight ContrastBackground script, to highlight the areas in question. In addition to the edge issue, the Pix script also highlighted an area at image top right.

    After searching the forums, I should also say that I don't have any infrared cameras in the area, and I have used black electrical tape to tape over most, if not all, tiny external blinking LEDs in the area.

    Thanks, Nick
     

    Attached Files:

  2. Mark McComiskey

    Mark McComiskey Standard User

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    I have exactly the same phenomenon on my darks and bias images, including the "ripple" of light that appears just to the right of the dark edge. I'm working with three people to try to eliminate these through calibration, but with little luck so far.
     
  3. Mark McComiskey

    Mark McComiskey Standard User

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    Nick - is there any chance you could post a link to some of your bias frames and dark frames? I would like to see if the dark edges and ripple on the left calibrate out. As I mentioned, I am having a devil of a time getting them to calibrate out on my camera, and am trying to determine if it is a problem with my camera/software set up (i.e. something I can fix my changing something in my setup/workflow) or with the model in general (in which case, one just has to live with it).
     
  4. Colin Haig

    Colin Haig Staff Member

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    Nick, I had a fast look at your FITS image. It looks like it was created with TheSky Version 10.5.0 Build 12978 (64 bit), and it has a pedestal of -100 applied.
    I see the normal left edge DC recovery effect. That should just subtract right out.
    I don't see much of any amplifier glow, which is a bit odd. Usually it is a bit more prominent. Perhaps TheSky subtracted something from the image?

    I don't know what you did to get that PixInsight image (pngs aren't useful - we can't assess the data).
    If you stretch an image to the extremes like i suspect you did, you'll see all the variations across the chip.
    It doesn't look like you have any kind of obvious light leak or camera defect.

    Could you follow these steps:
    1. Check if you have the current Firmware in the camera. SBIG Driver Checker, Firmware tab, check for update.
    2. Check the sbigudrv.dll driver version is 4.99 build 7, (no need to update to 5.0.x), and report what you have.
    You don't have a new 10-slot filter wheel, and I don't know how TSX will behave with the 5.0.x driver.
    3. Cool the camera down to a typical operating temperature (eg. -30C setpoint unless it's too hot at night right now) and let it stabilize for 60minutes.
    4. Use CCDOps or MaxIm DL Pro to take a set of unprocessed, unbinned (1x1) full frame (4096x4096) images.
    Check that you do NOT have RBI Pre-flash turned on, or the internal IR LEDS will light up the chip; usually this will show any polishing marks as swirls, or gradients in the image.
    Ideally, 10 bias frames; and 10 dark frames with exposure times from 5 minutes to 20 minutes.
    5. Send the images over via Dropbox / Google Drive / WeTransfer.

    To eliminate a couple of other possibilities, you could power off the camera, and remove the filter wheel AUX I2C cable and AO-X AUX I2C interface cables to ensure any internal sources are not generating light. (The AO-X has a red LED indicator that can create a reflection under some circumstances, depending on which serial number batch it is from).
    Make sure you have the camera stack capped properly.

    Let us know what you find. If you still get something you don't like, send over the image data, and we'll have a look. Include the serial numbers of all hardware and when you bought it.
    If the camera is more than 1 year old, have you recharged the desiccant? Frost on the sensor itself can do odd things. You could try taking bias and darks at +5C setpoint and see if they are significantly different.
     
  5. Mark McComiskey

    Mark McComiskey Standard User

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    Colin - the amp glow you reference in your response - is that inherent to the camera, or are there operational practices that can be followed to eliminate it? On my camera it is small enough a phenomenon that I can crop it and calibration eliminates the rest, but if there is something one can do to eliminate or minimize it, that is obviously for the better...
     
  6. Colin Haig

    Colin Haig Staff Member

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    It is inherent to the semiconductor detector, eg a CCD or CMOS APS sensor.
    Virtually all CCD cameras have some level of amplifier glow - it is usually in 1 to 4 corners of the detector.
    CMOS cameras are different - they have "logic glow" usually along 2 edges, sometimes with a larger patch in the middle of one side for Sony CMOS devices, and it is usually more pronounced than their CCD counterparts.

    Calibration is the way to eliminate it. Subtracting a dark frame of the same duration is the simplest.
     
  7. Mark McComiskey

    Mark McComiskey Standard User

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    Thanks much.
     

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