STX16803: shutter? and odd banding?

Discussion in 'STX and STXL' started by Paul M, Jan 30, 2019.

  1. Paul M

    Paul M Standard User

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    Hello DL support (and Doug)

    STX16803, FW7, STXGuider, AOX
    A couple of issues.
    1. occasionally get a frame that appears as a shutter issue. The camera does use 50mm square filters? This is very intermittent, and some nights happens once, and other nights not at all. Happens regardless of ambient temperature. Site temperature hardly ever gets below 0C.

    2. some odd banding in frames (the camera was received new in July 2018), so doubt it's a desicant issue?

    keep in mind the camera is 2500 miles (4000km) away at a remote site, so can't easily pull it off and look at it or bench test it.

    I've attached zip files of the fits, and small jpgs for easy viewing.

    thanks,
    ...paul.
     

    Attached Files:

  2. Doug

    Doug Staff Member

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    Those look like wafer polishing marks. I bet you have the RBI mitigation IR Preflash turned on. That's what makes the polishing marks show up - the preflash saturates the sensor with IR photons so the deep substrate traps are filled consistently.

    Unless you really need RBI mitigation for a specific field (e.g. an extremely bright field star), I would turn that off.

    That one image does look like the shutter did not fully open. The filter wheel wouldn't be exactly horizontal because it rotates. I'd try upgrading the firmware; we recently increased the shutter motor torque. That might resolve the problem. Otherwise it will have to go in to Bill.
     
  3. Paul M

    Paul M Standard User

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    thanks Doug,
    no idea why preflash would be on, but will surely check the settings.

    will check the firmware version and update.. (and SBIG checker).
    cheers,
    ...paul.
     
  4. Kevin Morefield

    Kevin Morefield Standard User

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    Doug,

    I'm trying to resolve the random upper left corner brightening on my STX. I understand it is a form of RBI. Last night I turned on RBI flash in CCDops, which seems to "stick" when I'm using TSX for camera control. Anyway, Lastnight's images did not have any of the upper left corner brightening (Yay!), but I got the exact same banding Paul showed in his attached images (Boo). I ran some darks in the morning to confirm and then ran darks without the RBI flash on and they disappeared. So I can confirm that this is from RBI flash.

    But how do I resolve the upper left corner problem? I have a least some brightening in at least half my subs and it is really strong in ~10%. Are there settings that could tame either the RBI flash banding or the corner brightening?

    Thanks,

    Kevin Morefield
     
  5. Colin Haig

    Colin Haig Staff Member

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    Doug this is the item I mentioned about TSX and RBI so you will ahve context.
     
  6. Doug

    Doug Staff Member

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    Let's not conflate corner brightness with banding due to RBI mitigation. They are different things.

    Most likely culprit for the bright corner is something to do with the readout amplifier. It's supposed to turn off on longer exposures, and then turn back on again shortly before readout starts. If it doesn't do that for some reason then you will get amp glow (LED effect from the readout transistors).

    First step - download the latest SBIG Driver Checker. Please do not use the Update button; I want to make sure you have the latest driver checker not just the driver.

    Next, use the driver checker to update your drivers.

    Third, use the driver checker to update the camera firmware. NOTE: Do not turn off power or abort the firmware download or you might brick your camera.

    Then test again and see if you still have the effect. If you do, then please try it in CCDOPS and see if you still get the effect.
     
  7. Kevin Morefield

    Kevin Morefield Standard User

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    Doug,

    Downloaded the latest driver and firmware. Only the firmware wasn't already up to date. Ran a night with TSX camera control and got the usual variable brightness in the upper left corner. I shot a 10 minute dark this afternoon using CCDOps and see the upper left brightening with CCDOps as well.

    What's the next step?

    Thanks,

    Kevin
     
  8. Doug

    Doug Staff Member

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    We'll have to see if we can replicate the behavior here.

    Please advise as to the exact operating conditions - cooler temperature, exposure duration, etc. We'll see if we can get the same result.
     
  9. Kevin Morefield

    Kevin Morefield Standard User

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    Doug, Here's a link to the dark frame .fit. Hope you can access:

    https://www.dropbox.com/s/74vrrgs2uq0nsy0/CCDops 600 dark 1.FIT?dl=0

    This particular frame is a 600 second, 1x1 dark at -30. CCDOps seems to save the image rotated 90 degrees clockwise compared to TSX so the bright corner is the upper right here. This is about an average amount of brightening I would say. I can be less or more. It varies with each sub. Of course it is more obvious on narrowband because the total counts of signal are lower. This doesn't appear on bias frames. I don't see it on flats, of course because it is swamped by the signal. But typical darks and lights, which range from 300 to 1200 seconds for me show it.

    Anything else you need? If you like you can dial into the camera and try it out yourself - it is at SRO.
     
  10. Doug

    Doug Staff Member

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    The FITS header shows a "Rotate Clockwise" command was run on it.

    I'd like to see a second frame. This isn't a problem if all the frames come out the same, because it will subtract during calibration. Can you provide another frame that doesn't exhibit this behavior, taken with exactly the same settings?
     
  11. Kevin Morefield

    Kevin Morefield Standard User

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    Here's another 10 minute 1x1 -30 dark. https://www.dropbox.com/s/393xx120mz7g0vf/CCDops 600 dark 2.FIT?dl=0

    Since the issue is really with lights, I thought it would be interesting to take a 1 second light and then shoot the 10 minute dark. (the roof is close so 1 second didn't blow out the exposure). Here's that one. https://www.dropbox.com/s/55p2w4cw4p2icke/CCDops 600 dark 3 following 1 sec light.FIT?dl=0
     
  12. Doug

    Doug Staff Member

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    Can you do a couple of light frames with the camera fully capped so there's no light? If your theory that this is lights versus darks somehow then they should be different from the "real" dark frames.
     
  13. Kevin Morefield

    Kevin Morefield Standard User

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    The Camera is in a remote site on a Planewave CDK14 so I don't have a way to cap the scope. It's not a theory about lights, the problem is that all of my lights have some varying amount of corner brightness. The darks get it too to some degree. But since it varies there is no way to calibrate it out.

    It's easy for me to give you examples of lights showing the variation in corner brightness - it would just be images captured with the TSX camera capture. The darks I've managed to capture with CCDOps don't look any different from what I see with TSX capture. I would offer to capture a few manual light frames with CCDOps but it looks like the next week at SRO is closed roof due to weather.

    It seems like you've not seen this problem before. I've seen it on several other guys 16803's - it seems to be a common issue. Adam Block even has a tutorial on how to remove this in processing from his 16803 images. I have to crop or fix every image I shoot. Here's what Adam's corner looks like in his tutorial :
    https://www.dropbox.com/s/4xabp8z4b4vq4xo/Adam block tutorial snip.JPG?dl=0

    Here's a pretty relavant summary from John Hayes where the corner brightness issue comes up:

    "Corner amp-glow in the 16803 always appears to be variable. As the trap charge leaks down, the amp-glow diminishes with each exposure. You either have to toss out a few initial frames or put up with gradients in the stacked data, which will vary depending on how many of the initial frames are included. Amp-glow in the initial frames can be reduced by taking 50-100 bias frames before the sensor is cooled. This trick works pretty well but it still doesn't make the glow perfectly repeatable because it relies on trying to empty the charge traps while the sensor is still warm. Properly implemented, pre-flash completely fills the traps so that amp-glow is totally eliminated. In order to be done correctly, the pre-flash sequence has to completely fill the bulk charge traps. I personally use a cycle of 5, 0.5 second flashes for each exposure to fill the traps."

    https://www.cloudynights.com/topic/605383-how-does-one-mitigate-the-rbi-in-their-16803-sensor/page-2

    Post #44 and #48 are most relevant.
     
  14. Kevin Morefield

    Kevin Morefield Standard User

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    OK so here is a theory. Thinking about how John described the issue, I looked back at sequences of my last night of light images. The initial image for the first object had a corner brightening and that faded for a few images and then came back. I checked and right before it came back a refocusing had occurred. The initial image for the second object also showed brightening and that had just followed a series of plate solves. Then a few light images later the brightening re-0curred. That was right after a re-focus.

    So it would appear that this residual charge is likely related to focus and plate solve events, both of which use a fast download speed. Would it make sense that these fast downloads could leave some residual charge?
     
  15. Doug

    Doug Staff Member

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    Don't use the Fast Download option. It's obsolete. It's only there to support old camera models, and might degrade image quality on newer cameras with no speed benefit. (Personally I would prefer to remove the option, but users of obsolete camera models want it there.)
     

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