Digital SLRs and dust?

Discussion in 'Digital Cameras' started by Dick Campbell, Sep 19, 2003.

  1. I hadn't thought of this until I saw a recent post but apparently there is a
    problem with dust getting on D SLR sensors. On film cameras the dust would
    be on the negative and only affect one picture but on a digital camera it
    would affect all subsequent pictures.

    Attempting to clean the dust off could tend to create more problems.

    Would a solution be to have an optically flat glass barrier just inside the
    lens mount so that the sensor chamber can be effectively sealed? If not,
    what is the reason this can't be done? If so do any D SLRs have such a
    barrier?

    I suggest the location because while having the barrier on the focal plane
    would protect the sensor, any dust there would have the same visible effect
    as no barrier.

    Dick Campbell
     
    Dick Campbell, Sep 19, 2003
    #1
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  2. Dick Campbell

    Bob Hatch Guest

    I have 3 DSLR's. 2 D30s and a D60. I've used them for a couple of years and
    10s of thousands of images and have never had dust on the sensors.

    Always turn the camera off when changing the lens.

    When in the camera bag always keep a lens or cover on the camera.
     
    Bob Hatch, Sep 19, 2003
    #2
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  3. Dick Campbell

    Chris Carlen Guest


    I don't think this is right. The charge is separated over an extremely
    small distances within the pixel structures themselves, not between the
    camera sensor and the "ground", thus there is no electric field
    emanating from the sensor to attract dust.

    I think they just collect dust due to surface phenomenon
    (Van-der-Walls?) like other very clean and smooth surfaces.

    There is one other possibility, that the non-conductive surface of the
    filter plate covering the sensor can hold a small amount of static
    charge. This could attract dust. But it is important too understand
    that this static charge is deposited by frictional processes as is the
    case with typical insulator rubbing charge accumulation phenomena, not
    as a result of the optical charge transfer mechanism that is the basis
    of CCD operation.

    There should actually be no case in which such rubbing would occur on
    the sensor surface. Cleaning is done wet, though it is possible that
    charge could be deposited or liberated nonetheless when using nonionic
    solvents and extremely clean and nonconductive apparatus.

    What is recommended to clean sensors? Methanol or the ammonium
    carbonate solution typical of Kodak lens cleaner? Either one should be
    somewhat conductive and non-static charge inducing.

    Just some thoughts.


    Good day!
     
    Chris Carlen, Sep 19, 2003
    #3
  4. So it is OK to physically clean the surface of the sensor and even use an
    appropriate cleaning fluid? I would imagine that access to the sensor would
    be a potential problem.
     
    Dick Campbell, Sep 20, 2003
    #4
  5. Fortunately I don't actually own a Digital SLR yet so there'e no harm done.
     
    Dick Campbell, Sep 20, 2003
    #5
  6. Dick Campbell

    Rafe B. Guest


    Some models have an anti-aliasing (AA) filter on top of
    the actual CCD sensor.

    If your camera is NOT one of those, then you had better
    not touch the sensor at all, ever, with anything.

    And even with the AA filter, I'd be nervous -- even though
    there are several websites describing cleaning procedures.

    Question is, who are you going to believe?

    Canon, who say don't touch the sensor, ever -- or those
    guys talking about PecWipes and cleaning fluid?

    Who's going to pay to fix or replace your camera if the
    PecWipes guys are wrong? (Or even if they're right
    and you just didn't follow their procedures exactly right?)



    rafe b.
    http://www.terrapinphoto.com
     
    Rafe B., Sep 20, 2003
    #6
  7. Dick Campbell

    Crownfield Guest

    read your manual.
    use the recommended materials.
    http://www.photosol.com/

    there is no problem if you are careful.
    I have cleaned my S2 sensor several times.
    I check it before any important job.

    and he was right.
    don't listen to the idiots here.
    he just did not know one when he saw one.
     
    Crownfield, Sep 20, 2003
    #7
  8. Good advice! Except, a "REAL camera shop" doesn't necessarily
    have people knowledgeable in this area either!

    Yes, CCDs and CMOS sensors do have a charge that will make dust
    adhere to the sensor. That is why there is a special cleaning
    mode to the cameras: electronics on, shutter open but
    the sensor is not charged, so the dust will come off easier.

    The dust problem is relative and depends on your use of
    the camera and the environment. I'm skeptical
    about any touching, liquid or solid, of the sensor.
    I have heard good things about "Eclipse" CCD cleaner.
    So far, I've only had to use mild canned air on my
    2 DSLRs. But if you stop down dust becomes a real
    problem that isn't seen (as much) at apertures faster than
    f/8.

    Links to eclipse products:
    http://www.imagingspectrum.com/cgi-local/SoftCart.exe/ccdsupplies.htm?E+scstore

    http://www.prophotogear.com/photosol.htm
     
    Roger N. Clark, Sep 20, 2003
    #8
  9. Dick Campbell

    Rafe B. Guest


    This is a thoroughly useless remark.

    It is in fact a serious subject, and owners of dSLRs
    need to consider this matter and make a decision.

    Your sarcasm is completely unwarranted.


    rafe b.
    http://www.terrapinphoto.com
     
    Rafe B., Sep 20, 2003
    #9
  10. I assumed that this wasn't a serious suggestion.

     
    Dick Campbell, Sep 20, 2003
    #10
  11. Thanks for all the replies.

    As mentioned a few times, this is a subject that you need to have researched
    before buying a Digital SLR and certainly before you attempt to deal with
    any dust on the sensor.
     
    Dick Campbell, Sep 20, 2003
    #11
  12. Dick Campbell

    Chris Carlen Guest

    If the sensor is charged, then where is the other half of the charge. I
    mean, there is a law of conservation of charge, thus, if there is an
    accumulation of charge on the sensor, then charge of the opposite
    polarity must have accumulated somewhere else. The question then is,
    where else?

    I think that the answer is that the charge that is produced by the CCD's
    normal operation is all located in the sensor itself. That is, both
    polarities of charge are separated by only a small distance in the pixel
    cell. Thus, a simple consideration of the properties of electric fields
    arising from static charges will reveal that from the perspective of the
    outside of the sensor, there is no net charge on the sensor. Thus,
    there is no electric charge dust attraction phenomenon.

    If it is said that there is, then I would consider this to be photo
    equipment folklore.



    Good day!
     
    Chris Carlen, Sep 20, 2003
    #12
  13. Dick Campbell

    Rafe B. Guest


    It was a wise-ass gratuitous bit of sarcasm.

    Rubs me the wrong way, because I take this
    issue seriously.

    The dust issue is real. The solution is elusive,
    and if done improperly, can ruin the camera.

    I just don't see any humor in this matter.


    rafe b
    http://www.terrapinphoto.com
     
    Rafe B., Sep 20, 2003
    #13
  14. Dick Campbell

    Don Guest

    I live in amongst a pinus radiata forest/plantation and own a 10D.
    Currently the pines are releasing pollen and everything, and I mean
    everything is covered in yellow dust (pollen). Apart from the sneezing
    problem when trying to shoot shots, the pollen covers the lenses and I never
    never change lenses outside. I have found that prior to using lense wipes
    etc it is critical to use a blower followed by a soft brush on the lense
    prior to the wipes. I am very careful about changing lense and have had no
    problems to date with dust or pollen.

    regards

    Don
     
    Don, Sep 20, 2003
    #14
  15. Dick Campbell

    andrew29 Guest

    CCDs only use a charge of about 15V, which is nowhere near enough to
    attract dust.

    Andrrew.
     
    andrew29, Sep 20, 2003
    #15
  16. Dick Campbell

    Chris Brown Guest

    In the case of the digital EOS range (at least the 30/60/10 and probably 300
    - don't know about the 1 series), you can't touch the sensor because the
    antialias filter is in the way. What people mean when they complain about
    "sensor dust" is actually dust on the antialias filter. Your camera manual
    should advise on the best way of cleaning it.
     
    Chris Brown, Sep 20, 2003
    #16
  17. Dick Campbell

    Rafe B. Guest


    It does, but the recommended procedure is only
    marginally effective.

    The "recommended procedure" suggests a blower
    bulb and never touching the sensor surface (or AA
    surface, if you will.)


    rafe b.
    http://www.terrapinphoto.com
     
    Rafe B., Sep 20, 2003
    #17
  18. 1) Dust particles can have electrostatic charge. Put any
    charged particle in an electric field, even a small field
    and the particle will move, in this case if it can
    overcome air turbulence (probably in only a
    few volts/meter field).

    2) The ccd/cmos sensor electronics create an electric
    field in order to collect the electrons, liberated by
    the incoming photons, into what are called potential wells.

    3) The ccd/cmos electric field may use only about 15
    volts, but this is over a very small distance, like
    10 microns or less. Thus, the field strength is
    approximately:
    15 V / 0.00001 meter = 1.5 million volts/meter (!)
    inside the sensor. (How much field strength makes it
    outside the sensor I do not know, but it is certainly
    enough to attract dust.) The Canon battery is 7.4 volts.
    If the potential well is about the size of the sensor,
    7.4 microns, the field may be about 1 million V/m.

    4) Since there are many potential wells in in an array,
    the electric field is not a point source, so does
    not fall off as 1/distance squared.

    5) Any dust particle with a static charge that
    gets close to the ccd/cmos sensor when the shutter is
    open may get attracted to the sensor.

    Fortunately, shutters are open relatively short times.
    The problem is, if you get dust inside the camera during
    lens changes, when the shutter opens, the dust can be
    stirred up and attracted to the sensor.
    Thus, BEFORE cleaning your ccd/cmos sensor, clean the
    inside of your camera.

    (What I do; no guarantees:)
    I use optics-safe canned air and gently blow out the inside
    of my cameras (film too) with the shutter closed. I start
    the canned air flow pointing up at a gentle level, then
    holding the camera opening facing down, I move the
    camera into the air stream. I only move the camera and
    not the air, so no spurts come out of the can. Same
    for cleaning the ccd/cmos sensor, but using a gentler rate
    (e.g. a mostly empty canned air). I personally do
    not like the rubber bulb idea because in the process of
    squeezing the bulb, the tip moves, and I don't want to
    accidentally touch something. Don't forget to clean the
    backs of your lenses and the cap that goes on the
    back of the lens.

    Serious comments welcome.

    Roger Clark
    Photos, digital info at:
    http://www.clarkvision.com
     
    Roger N. Clark, Sep 20, 2003
    #18
  19. Dick Campbell

    andrew29 Guest

    Not much: the anti-aliasing filter is pretty thick in comparison with
    these dimensions, and the dust is (hopefully) on the other side of
    that filter.
    That's the potential gradient inside the chip, not outside it.

    I'm not arguing that the filter builds up a considerable static
    charge. But that static charge isn't necessarily caused by the
    electronics. It could easily build up such a static charge without
    the CCD being powered.

    Andrew.
     
    andrew29, Sep 21, 2003
    #19
  20. Dick Campbell

    JPS Guest

    In message <>,
    On my 10D, it is the focusing screen that seems to be the biggest
    attractor of dust. It almost seems as if *it* is charged.
    --
     
    JPS, Sep 23, 2003
    #20
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