Digital camera with dark spots on photos

Discussion in 'Mobile and Portable' started by johnye_pt, Jul 27, 2018.

  1. johnye_pt

    johnye_pt MDL Addicted

    Aug 26, 2010
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    I was not sure where to ask about this, but it probably applies to anything with a camera lens.

    A few days ago, I picked up my old Mustek MDC-5000 digital camera (3.1MP, and 5.0MP hardware enhanced) and noticed that every photo taken had 5 or 6 dark spots always in the same locations. After googling a bit, the explanation was dust somewhere in the internal lens.

    I took the camera apart, and found out that a square piece of blue transparent plastic has mysterious "internal bubbles" that I'm not able to remove.

    All the pieces included in the lens part are: CCD -> blue transparent plastic -> small lens -> piece of plastic with a hole smaller than the lens (fixed aperture?) -> another small lens.

    Does this blue piece of plastic have a special feature like filtering some kind of light/colors, or can it be replaced with another "normal" piece of clear or blue transparent plastic?
     
  2. TigTex

    TigTex MDL Member

    Oct 5, 2009
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    If you zoom the picture and the dark spot is exactly 1 pixel, you have dead pixels on the sensor and that is common in older digital cameras.
    If not that is probably a polarizing filter or UV filter and you can try to use it without that plastic and see what happens. It may cause brightness and color inconsistency on the picture

    Boa sorte
     
  3. johnye_pt

    johnye_pt MDL Addicted

    Aug 26, 2010
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    Nope, I was eating cotton candy when I took that photo.
     
  4. Yen

    Yen Admin
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    May 6, 2007
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    #6 Yen, Jul 29, 2018
    Last edited: Jul 29, 2018
    The bluish transparent square part (film) is usually the first filter of a CCD (charge coupled device sensor). It is an infra red (IR) filter. Beneath of it there is a Bayer CFA (color filter array / RGB mosaic). The corresponding process the cam has to do is demosaicing.

    When light reaches the CCD the infrared part needs to be filtered out first. It'd cause unnecessary heat and other disturbances.
    CFA is the interesting part.

    If you wonder how a sensor can recognize colors at all then you might want to know more about Bayer-to-RGB conversion.
    Actually a sensor is color-blind. It can only recognize how much light is on a pixel of it. And if there is too much, you get clipping. (histogram).

    Short. Due to heat and humidity / age I think the IR film's glue or the filter itself got bubbles due to expansion and / or there were micro bubbles already which have grown. It's a quality issue...

    Actually nowadays the IR film is a part of the CCD itself. Its removal attempt would also damage the CFA beneath, means the functionality of the entire CCD...

    But yours seems to be separated from the CCD or an additional one. You'd need to find a replacement IR film (IR cut-off-filter) with the same physical dimensions and attributes. OR you can try without it IF you care about heat (direct sun light etc.)

    Using it without IR filter might have an impact on the automatic white balance of the cam, though. If you encounter issues you might try it by using manual white balance to compensate the issue if the cam is capable of manual white balance.


    Be careful actually nobody ever should touch the surface of a sensor. It's very sensitive to physical impact like scratches and fingerprints. Modern complementary metal-oxide semiconductor (CMOS sensor cams) have built-in ultrasonic cleaning. CMOS tech is superior to CCD, but more expensive.
     
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  5. johnye_pt

    johnye_pt MDL Addicted

    Aug 26, 2010
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    Thank you for the explanation. Luckily while disassembling it I never touched nor tried to clean the sensor, because there was nothing to clean. I guess I'll just put it back in the box for now and attempt a repair later when I get the right material. It's an outdated camera but it's always nice to learn about these things and it feels great when we can (hopefully) repair it ourselves.