Resolved STXL16200 vertical lines

Discussion in 'STX and STXL' started by Vipin Kamath, Aug 4, 2017.

  1. Vipin Kamath

    Vipin Kamath Standard User

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    Just got my STXL16200 yesterday. I notice vertical lines in my test grabs in CCDOps. Here's a 3 sec grab with dark frame.

    https://drive.google.com/open?id=0B9LrVdiNAR75MFp5RExCdUtOTkE (it's a 30MB file)

    Do I need to tweak any settings? I used the included power brick and USB cable. This was taken indoors (waiting on spacer to install on scope).

    I will be running this eventually using SGPro.

    Any pointers would be appreciated.

    Vipin
     
  2. Doug

    Doug Staff Member

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    You have auto-dark turned on; those are actually hot columns being improperly subtracted. A certain number of hot columns are normal per manufacturer specifications.

    It also looks like you don't have the cooler operating. The unregulated cooling is the reason the columns didn't subtract properly.

    So:

    1. Turn the cooler on and set it to -20C. Wait a few minutes for it to fully stabilize and regulate.
    2. Now do an exposure with auto-dark turned on. (If you ran an exposure before it stabilized, change the exposure time slightly to force it to shoot a new auto-dark.)
    Now you won't see any columns.
     
  3. Vipin Kamath

    Vipin Kamath Standard User

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    Doug, Thx for the quick response. Will try this tonight. When I eventually get to SGPro, I suppose I would have to do lights and darks separately, right?

    V
     
  4. Doug

    Doug Staff Member

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    Usually you avoid doing auto-darks, that's for "quick look" situations. You would collect images without calibration, and collect the darks separately (before or after). You want to take darks with the same CCD temperature and exposure time as your light frames. You can build a library of darks that you can use over time. I usually refresh my darks every six months or so, or if I see a sudden change (you will occasionally get radiation damage that causes a new hot pixel or column.)
     
  5. Vipin Kamath

    Vipin Kamath Standard User

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    Thanks Doug. Will keep you posted after I follow your instruction above.
     
  6. Vipin Kamath

    Vipin Kamath Standard User

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  7. Jared Willson

    Jared Willson Cyanogen Customer

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    I'm a fellow 16200 owner, and I just downloaded and took a look at your 10 minute "Take 2" dark to see if it was similar to one of mine. It's not. I think you may still have autodark subtraction turned on since it shows dark pixel artifacts that would typically come from subtracting a single dark from a single dark. In other words, I see cosmic ray strikes and "worms" in your sample.

    The other thing I noticed was a really weird gap in your histogram. Lots of very dark values, then no medium dark values, then lots of lighter grays. Also, your pixels vary from a value of 0 to about 200 ADU--much lower than it should be. Again, I think you may have autodark subtraction still turned on.

    What program did you use to grab these frames? Was it Maxim? Or CCDOps? I might be able to give you pointers on what settings you should double check...
     
  8. Jared Willson

    Jared Willson Cyanogen Customer

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    Oh, just noticed that Doug was advising you to do a dark with auto-dark turned on. Not certain why, but he's the expert so...

    Given that auto-dark was enabled, your exposures look pretty normal to me. Not certain what the gap in the histogram is about (when viewed in Maxim), but mine does the same thing, so it's probably normal. Probably something to do with quantization error when you are close to the pedestal.
     
  9. Doug

    Doug Staff Member

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    No, I did not and do not recommend using auto-dark.
     
    Bill likes this.
  10. Jared Willson

    Jared Willson Cyanogen Customer

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    My mistake, Doug. I misinterpreted your post where you said, "Now do an exposure with auto dark turned on". Clearly you meant a "quick look" light exposure, not a dark with auto-dark subtraction.
     

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