Weird hot pixel behavior in darks

Discussion in 'STT Series (obsolete)' started by JoshuaFrechem, Jan 12, 2019.

  1. JoshuaFrechem

    JoshuaFrechem Cyanogen Customer

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    Hello, I just made a new master dark for my 300s exposures and saw something that I have only seen with charge transfer issues. This is a stack of 65 at -20C. I don't see noticeable CTE issues in light frames, which makes me believe that is not what this is. Is there some property of the sensor that causes a high likelihood of a fairly high pixel value directly next to it that isn't CTE? Nearly all of the hot pixels have this cascading effect. It didn't just instantly show up. I have seen it before, I just don't remember when I noticed it. My sky brightness is really high with pretty bad seeing that could be disguising a CTE issue IF there is one, but I am inclined to believe it is coincidence or there is some other reason this could happen. Any ideas or comments? The FIT file was too large to attach directly, but I can upload a cloud link with the file to look at the FIT.

    Thanks,
    Josh
     

    Attached Files:

  2. Colin Haig

    Colin Haig Staff Member

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    Josh, maybe you could post a dropbox link with a FITS of the stack and maybe a couple sample files original files included to make the stack.. I think I see what you are talking about, but it doesnt quite look like a CTE.
     
  3. Doug

    Doug Staff Member

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    I'll need a FITS image to be sure - please upload a single unprocessed dark frame. It could indeed be a hardware problem, but we do test every camera we manufacture for trailing charge, so this must have developed recently.

    There are several plausible hardware failures that could cause that behavior. It could be either CTE caused by bad clocking voltages, or it could be a problem with the amplifier chain.

    What is the serial number of your camera?
     
  4. JoshuaFrechem

    JoshuaFrechem Cyanogen Customer

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    Here is a link to a folder with the master and 10 of the raw frames from 2 different nights (I combined darks from 3 nights in the master, but only a few days apart). Unfortunately, I don't see the same issue in my 600s dark from summer. I see it a little bit in my 600s dark from fall.

    https://drive.google.com/open?id=1B58j4wSkRuMwiTYxBf2cNBm8XWdf-pJT

    Serial number is: T14030671
     
  5. Doug

    Doug Staff Member

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    Well this is a little odd. On the one hand, it's well within our trailing charge specifications. You can't even see it unless you stack a large number of frames. Plus, looking at the whole frame statistically it amounts to 0.01%. At the same time... while there's none of this effect on the left side of the frame, if you isolate the area on the right side it increases to 0.3%. Still well within spec, but a little odd.

    Can you actually see this effect in your final images?
     
  6. JoshuaFrechem

    JoshuaFrechem Cyanogen Customer

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    Virginia
    I am in a white zone and have horrible seeing. My conditions, I suspect, mask the possibility of seeing it in final images. Background is really high and the FWHM of LRGB images is, on average, around 3.8", about 5-6 pixels. I am just hoping it doesn't get worse since it appears to be doing so.

    Is it possible that moisture has built up in the readout electronics from operating in a 90%+ humidity environment for a while? I have a lot of molecular sieve I can place it in, put it in a desiccator, Argon purge, bake... Would anything like that help?
     
  7. Doug

    Doug Staff Member

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    I doubt it is humidity, but if there is some moisture problem there it is probably sufficient to keep the camera slightly warm. Keep it powered up, with the cooler turned off, when you are not using it.

    It may be that an internal regulator that provides one of the horizontal clock voltages has gone slightly out of spec. That might be indicative of a progressive failure, but since the camera is no longer under warranty I suggest you just keep an eye on it. If it progresses to an obvious failure then return it to Bill. That will make it easier for him to find the problem; as it stands now it might be difficult to diagnose and it could have to come up to Ottawa for engineering evaluation.
     

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