How do I know ST8300 needs dessicant replacing?

Discussion in 'STF Series CCD Cameras' started by Shailesh Trivedi, Dec 1, 2022.

  1. Shailesh Trivedi

    Shailesh Trivedi Standard User

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    I bought my ST 8300M circa 2011 before STF8300 was available. During the past year 2022, I have had a large amount of "hot pixels" which cannot be calibrated out, it seems they move around.

    I have not replaced the dessicant (ever), how do I know it should be replaced?

    Where can I purchase the dessicant? How do I change the dessicant (instructions)?

    Thanks for your help.

    Shailesh Trivedi
     
  2. Tim

    Tim Staff Member

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    If you have moisture, or frost forming on your sensor or inside the sensor chamber, it's time to either recharge or replace the desiccant. Here are some further details...

    https://diffractionlimited.com/why-desiccant/

    You can recharge your desiccant by following these instructions on page 39 of the manual below. This is an Aluma AC 4040 users manual, but the instructions for recharging the desiccant are virtually identical.

    https://cdn.diffractionlimited.com/downloads/SBIG_Aluma_AC_Series_Users_Manual.pdf

    If you would like to purchase a replacement desiccant plug, you can find them at the following web store link....

    https://diffractionlimited.com/product/replacement-desiccant-plugs/
     
  3. Colin Haig

    Colin Haig Staff Member

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    Hey @Tim - can you check that - I think that's not right for the older ST-8300, as it had the desiccant internal, instead of the external removable desiccant plug and @Bill had a solution.
     
  4. Tim

    Tim Staff Member

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    Oh my mistake. You are correct. There is no desiccant plug on the ST.
     
  5. Shailesh Trivedi

    Shailesh Trivedi Standard User

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    So how do I order one of those internal sachet?

    I am having what look like "floating" hot pixels. I am unsure if it is frost due to a saturated dessicant (a molecular sieve if I recall correctly) or due to a slowly dying sensor.

    Shailesh
     
  6. Colin Haig

    Colin Haig Staff Member

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    We would need some sample images to tell what is going on.
    e.g. sample bias, dark, and flat or light frames. Unprocessed, binned 1x1, preferrably taken with MaxIm or CCDOps.
    Since the files may be rather large, if you can't upload them here, you could zip them up and send a link via DropBox / WeTransfer or something like that. My email: chaig (at) diffractionlimited (dot) com
     
  7. Shailesh Trivedi

    Shailesh Trivedi Standard User

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  8. Colin Haig

    Colin Haig Staff Member

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    That link does not work. You need to share the correct link.
     
  9. Shailesh Trivedi

    Shailesh Trivedi Standard User

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    please provide your email in PM, I will share with your email
     
  10. Shailesh Trivedi

    Shailesh Trivedi Standard User

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  11. Colin Haig

    Colin Haig Staff Member

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    No, you need to look at SHARING in dropbox.
    OR Create a SHARED FOLDER.
     
  12. Colin Haig

    Colin Haig Staff Member

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    Like this:
    dropbox_share.png
     
  13. Shailesh Trivedi

    Shailesh Trivedi Standard User

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  14. Colin Haig

    Colin Haig Staff Member

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    Ok I got the files.
    The bias and dark were shot with TheSky X back in January - that's 11 months ago.
    The light was shot with SGP back in August - that's 4 months ago.
    You need to provide recent and consistent images in order for us to diagnose what is going on.

    Please redo these, so they are all taken with the same software, preferrably CCDOps, MaxIm, or all in the current version of TheSky X.
    Make the dark and light/flat the same exposure length, with the camera cooled to a stable temperature for at least 20 minutes so it settles down (eg -10C to -30C preferrably).
    I suggest you take a flat, perhaps pull the camera off the scope, put it on your kitchen table, and cover it with a stack of a few sheets of white paper, so we can see what is going on properly.
    30-60 seconds for flat and dark should be sufficient.

    The light frame is odd - a huge triangular swath of pixels that might be fine dust directly on the sensor glass or the start of tiny ice crystals, but usually there are tendrils, which I don't see.

    Please redo these.
     
  15. Shailesh Trivedi

    Shailesh Trivedi Standard User

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    Colin

    I know there are issues. I have already pulled the camera out of my scope. I prefer not chasing issues for reproduction. I can but now I have another CMOS camera on it. Can I purchase a dessicant from SBIG for this camera (still my favorite)? This will rule out icing and allow me to surmise that maybe the sensor is failing.

    I am having a hard time calibrating out with cosmetic correction (I have imaged with this camera all of 2022) since the hot pixels or whatever it is, is not constant and moves around, but this huge triangular swath of pixels remains though not constant. I checked the sensor, no dust was found on the sensor. I doubt it is on the filters since it persists on all filters. The swath is not new, so unsure how recapture will help diagnose anything.
     
  16. Doug

    Doug Staff Member

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    The old ST-8300 desiccant isn't user-replaceable, as there is no separate desiccant module. I recommend that you send it to @Bill.
     
  17. Shailesh Trivedi

    Shailesh Trivedi Standard User

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    @Doug I have been able to open up the 8300 and pry out the desiccant sachet (I believe it is a molecular sieve 0.25g don't know the size but it's tiny). So I can replace it myself if I need to

    @Colin Haig I recaptured dark, bias and flat frames - please check it at the same link https://www.dropbox.com/scl/fo/y3vv2knkzzc3oibuuhcyy/h?dl=0&rlkey=wmgkq1jt12fxb08gyqpdb9y5v

    The 5 min dark at -8.75C shows the same triangular pattern (could not cool it below - 12C indoors). Please suggest next steps.
     
  18. Doug

    Doug Staff Member

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    Yes, it is molecular sieve.

    We never recommend a customer open the chamber. The sensors are very sensitive to ESD, and dust contamination is hard to control without a clean room. Of course it's your camera and if you are willing to take the risk, then you can service it yourself.
     
  19. Shailesh Trivedi

    Shailesh Trivedi Standard User

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    @Doug I see your point. I would like to send it in for desiccant replacement and general testing. How do I do this?
     
  20. Doug

    Doug Staff Member

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    Please contact @Bill, bill at sbig dot com.
     
    Colin Haig likes this.

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