STXL-11002 TEC seems to be vibrating the imaging CCD

Discussion in 'STX and STXL Series Cameras' started by Jeburnett, Jun 24, 2016.

  1. Jeburnett

    Jeburnett Cyanogen Customer

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    I've come to this conclusion by empirical methods to eliminate every element until I found the source of what appears to be motion blur in my images. This problem started back in March and I've been trying to figure it out ever since. The short story is, I was able to remove other possible causes yet the blur remained UNTIL I turned of the TEC cooler on the camera. Like a light switch, the problem comes and goes when the cooler is on and off. The fan is NOT the cause because it is left off for now. Purely electronics at play and I wonder if there's a component buzzing on the circuit board since the Peltier is not piezoelectric (as far as I know).

    Example images attached (unbinned, unguided 60 second, without a filter)

    I have MANY more example images some with other interesting patterns of motion.

    Thank you,
    Jonathan
     

    Attached Files:

  2. Jeburnett

    Jeburnett Cyanogen Customer

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    I need to add one more observation to what I said above. All of my testing was done remotely so I was not next to the camera during all of these tests, so when I mentioned that I had turned off the camera fan via the driver control, I assumed that it was off and stayed that way. What I just learned while standing next to the camera is that either the camera or the driver controlling it will autonomously turn the camera fan on, first at low speed and later to high speed and back and forth EVEN though I have unchecked the fan enabler in the application (TheSkyX). What that means now is that when I thought I had eliminated all sources of mechanical vibration, I may have not really accomplished that because I trusted the driver control to honor my requests.

    So what does this mean? It means that if the fan was coming on every time I was enabling camera cooling, then maybe the fan could be the source of some vibration. I cannot detect any vibration be touching it while it is blowing but perhaps the magnitudes that are visible on a micron scale wouldn't necessarily be something I could feel.

    One more piece of information; when the distortion is happening, it occurs with a specific pattern, that moves by the same number of degrees as the camera if I rotate it. I've started to wonder if the chip carrier (or whatever the CCD holder is called) might be a bit loose in one axis, making it susceptible to vibration in that one orientation?
     
    Last edited: Jun 26, 2016
  3. Tim Puckett

    Tim Puckett Guest

    Jonathan, I could be when you turn on the cooler the fan slows down just a little to a resonance point.
    I will bet you its the fan. You are on-site now to test it right?
     
  4. Jeburnett

    Jeburnett Cyanogen Customer

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    Yes I am Tim.
     
  5. Jeburnett

    Jeburnett Cyanogen Customer

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    Did you have something you wanted me to try?
     
  6. Robert Mueller

    Robert Mueller Standard User

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    Jonathan,
    Have you gotten any further diagnosing this issue? I'm very interested in this as I seem to get sporadic elongation like this using my STXL and MX mount. I see images similar to yours even with short exposures sometimes that should rule out tracking errors.

    I may get a chance to do a similar test over the next few days.

    Thanks,
    Robert Mueller
     
  7. Jeburnett

    Jeburnett Cyanogen Customer

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    Hi Bob,

    Yes, I've been in contact with Bill Lynch (who is on vacation) and he feels very strongly (like Tim) that this is a cooling fan problem. He plans to send me another fan when gets back to work next week and then I can confirm. You can verify if the fan is the problem for you by taking a picture with the camera's cooling turned off. Disabling the fan in software won't override the camera's self-preservation mode which turns the fan back on when the heatsink gets too hot. I'd recommend cooling the camera down fully to -35C, take an image to confirm the stars are showing motion blur, then turn off camera cooling and give it about 45 seconds to ramp down to 0% power consumption. Then take another image and compare. Be sure first that you've instructed the camera to not run the fan when powered (which won't stop it from running when cooling) but this will ensure the fan is stopped when the cooling power has reached 0%.

    Hope this is helpful.

    Jonathan
     
    Last edited: Jul 3, 2016
  8. Robert Mueller

    Robert Mueller Standard User

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    Thanks Jonathan...I'll let you know if Isee similar behavior.
    Robert
     
  9. Jeburnett

    Jeburnett Cyanogen Customer

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    Bill kindly sent me a new fan when he returned from vacation and I installed it. I also used the opportunity to thoroughly clean the camera, filter wheel and AOX of massive accumulations of dust and pollen. I also baked the desiccant cartridge while at it. So with great anticipation I rolled out for star test to confirm that the vibration effects were eliminated. Unfortunately, I wasn't able to tell because the camera is now doing something very different. Here's an example of an image I took of Arcturus, presumably centered in the FOV (but for obviously reasons, I can't confirm):

    Every_30_degrees_1x1 60.000secs00000463.jpg

    I've taken many different kinds of shots including short exposures, long exposures, darks, binned and unbinned and the results are the same though the brightness lessens with shorter, unbinned exposures (as stars would naturally). I've never experienced this before and naturally, I'm feeling like perhaps my cleaning caused this, but even that too, I've done several times before without an issue.

    One final bit of information; I used the autoguider to take an image and with the exception of the tear drops, that image looks normal:

    00008875.Alphecca.jpg

    I last test image that might be helpful (not to me but maybe to you) was a shot of the full moon:

    Every_30_degrees_1x1 0.100secs00000450.jpg

    I've tried this kind of testing on a couple of different nights but the results aren't really changing. I've peered into the telescope to watch the camera's shutter open and close and all that appeared to happen normally. Finally, I did consult with Bill who said he'd never seen anything like this. About the only thing I haven't tried is to tear the camera back apart, inspecting it for anything my eye might detect, but I thought it best to post here first in case you want me to try additional things first. In case you want to inspect some of the test FITS, here's a DropBox link: https://www.dropbox.com/sh/koo1j9r5br8u17q/AAD5HRAXoAKcBHoFWZUZX6Ipa?dl=0

    Thank you,
    Jonathan
     
    Last edited: Jul 25, 2016

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