Sensor dust Nikon D80

Discussion in 'Nikon' started by Guest, Jan 9, 2008.

  1. Guest

    Guest Guest

    Hi,

    just getting my head around digital SLRs.

    As the D80 has a mechanical shutter, would this not prevent ant dust
    getting onto the sensor while the lens is being changed.

    or can the dust 'get' around the side of the shutter mechanism?

    thanks
     
    Guest, Jan 9, 2008
    #1
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  2. Guest

    Guest Guest

    um, no it doesn't.

    however, dust will eventually get on the sensor, at which point you
    activate the mirror lock up mode (for cleaning, not shooting) and give
    a blast of air from a rocket blower (*not* a pressurized can of air).
    that should dislodge most instances of dust.
     
    Guest, Jan 9, 2008
    #2
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  3. Aehmm, no.
    But the shutter opens when a picture is taken, if there was dust in the
    mirror box from changing lenses, then this dust may get disturbed by the
    mirror, pass the shutter, and get onto the sensor.

    jue
     
    Jürgen Exner, Jan 10, 2008
    #3
  4. Checking sources of information on the web about this I find that many
    of them are misinformed and get the science wrong. I checked because
    just on first principles this sounds improbable. The voltages involved
    in dust attraction are very high voltage static charges, whereas those
    involved in the operation of a digital camera sensor are very
    low. That's why you get dust attracted to the surface of a CRT screen,
    but not to the terminal of a torch battery. What is more, operability
    at the low voltages at which camera sensors work implies a
    conductivity which would not permit the development of dust attracting
    static charges.

    There could be a dust attracting static charge involved, but it could
    not be due to the low voltage electronic operation of the sensor. It
    could be due to some kind of transparent protective coating. However,
    the problems of static dust attraction in optical coatings are so well
    known to engineers, and so many ways are known of minimising these
    effects, that I'd be surprised if this was the case. As far as I know
    the camera sensor is protected by a glass screen, and that is what
    gets dirty and needs to be cleaned. I can't see why an optical glass
    screen should suffer any more from static problems than do your camera
    lenses.

    What is more, I note that some DSLR makers use various sensor
    vibration cleaning methods which they claim help to keep their sensors
    dust free. These would not operate in the presence of electrical
    static attraction. Nor would the special brushes that use static
    charged bristles to attract the dust, since they would transfer charge
    to the sensor and make things worse.

    But these are just educated guesses on my part, and I could easily be
    wrong. Do you have any good sources of information on this? I note for
    example that Wikipedia contains more superstition than science on this
    topic.
     
    Chris Malcolm, Jan 10, 2008
    #4
  5. A day late maybe, but my brand new D80 with firmware version 1.01 will
    go into lock up mode when the battery charge is at least as low as 74%
    (I just tried it).

    I don't know what definition other models and/or firmware revisions use
    for "fully charged", but for me at least it seems to be a bit less than
    "fully". ;)
     
    Central Scrutinizer, Jan 10, 2008
    #5
  6. That involves movement and mechanical work against the static
    repulsion which has to be engineered in the devices which exploit it
    and is unlikely to be found by accident in a digital camera :)
    The rubbing is doing the work. There is no rubbing in the operation of
    a digital camera sensor.
    And since such charges are very damaging to the camera's digital
    electronics, the engineers have arranged that there are no high qualiy
    insulators inside the camera capable of doing that.
    It's obvious you don't understand the physics, because that example
    supports my point, not yours. Because unless the battery is shorted
    out, any circuit it is connected to will keep a potential difference
    between the postive and negative terminals even when it is switched
    on. Same goes for a naked unconnected battery -- a low voltage
    potential difference. Yet we do not see a dust collecting differential
    between the two terminals of a battery left out in the open air.
    There is in the sense that some things unconductive enough to be
    considered insulators at low voltages are still conductive enough to
    leak off static charges, a fact that engineers often exploit in
    keeping static charges away from sensitive CMOS circuitry (a
    technology often employed in digital camera sensors, and almost
    always employed in the circuits connected to it).
    Check the physics of static attraction for the theory, or for a
    practical experiment check the differential dust collection between
    the termimals on a naked unconnected flashlight battery.
    In order to prevent the coating causing static build up problems, the
    engineers have arranged that it is not a good enough insulator to hold
    a static charge.
    That's not how it works -- the dust that glass attracts in dry air is
    charged dust. The charge (to begin with) is on the dust, not the
    glass. Unless you deliberately charge the glass by rubbing it with an
    appropriate cloth, and it happens not to be semi-conductive (which
    modern optical coated lenses often are on purpose) Which doesn't
    happen on the digital sensor.
    Energising the sensor does not involve voltages high enough to attract
    dust.
    Look up induction and transfer of static charge. It can't be avoided
    if you touch an uncharged perfect insulator with a charged one.
    Which will charge it up as every engineer knows unless special
    precautions have been taken to arrange a charge leakage path in either
    the surface or the cleaning material.

    You persist in thinking that the operating voltages of a digital
    camera sensor are enough to generate dust attractive static
    charges. That's very definitely false, although a lot of photographers
    who dozed during their school physics lessons do obviously believe that
    strongly enough to include the claim in educational materials they
    It mentions dust adhering to the sensor through electrostatic charges,
    a phenomemon (so it claims) that can also be observed on LCD and CRT
    screens. That, as I have already explained, is a common superstition
    amongst photographers without a basic physics education.
     
    Chris Malcolm, Jan 11, 2008
    #6
  7. Guest

    Anonymous Guest

    Would you mind amusing the class by trying to explain why you think
    batteries and static charges have any practical relationship here?

    /me opens a bag of microwave popcorn and waits for the inevitable
    "well, umm.... they're both electrical stuff" reply.
    You, sir, are a retard. It's nothing *but* physics that lays waste to
    all of your blubbering. Modern sensors operating on nothing *but*
    static charges and how photons dislodge electrons with stored
    potential, and as any 9th grade general science student can tell you
    the laws of conservation of energy deem that potential a problem for
    digital photographers no matter how dedicated engineers may be to
    "bleeding off" said charges. In fact, the very words from the engineers
    you're pretending to cite would give an intelligent being the clues
    they need to come to a logical conclusion about how static electricity
    affects dist inside a modern digital camera, and why it most certainly
    *is* a problem.
     
    Anonymous, Jan 11, 2008
    #7
  8. Perhaps not always, and not if it has good anti-static treatment, but
    it's not hard to find at least hundreds of volts on the surface of a
    non-static-treated CRT screen in dry air. And it's not difficult to
    produce thousands of volts by rubbing a suitable plastic on the sleeve
    of a pullover. The simple test is whether you can produce any kind of
    spark. The tiniest spark, just a little snap which is hardly visible,
    requires nearly 400 volts at normal temperatures and pressures. You
    can generate well over a thousand volts by stroking a dry cat in dry
    air with dry hands.

    Attracting dust through air to a charged surface requires a potential
    difference of at least hundreds of volts.
     
    Chris Malcolm, Jan 12, 2008
    #8
  9. Right, as will become clear.
    Try and follow the argument. I'm not claiming that it does.
    If the electrostatic charge is not sufficient to cause a potential
    difference of at least hundreds of volts it's not going to be able to
    attract a dust particle to it through air.
    No, but there is a minimum potential difference resulting from the
    charge necessary to attract dust through air.
    Insulation is relative to voltage. It's usually treated with something
    which will provide at least enough conduction to allow static charge
    to leak away. That can still be a good enough insulator at the
    operating voltages of a digital image sensor.
    I don't need to "find" that. I've spent years of my working life
    wearing those things.
    Which is why you might need even more than hundreds of volts in order
    for static charge dust attraction to be problem on digital camera
    sensors :)
    I will if you tell me something I don't know because you'll probably
    have got it wrong :)
    Because a potential difference of several volts, which is all that is
    involved in the operation of a digital camera sensor, no matter with
    how much charge, is far too little to attract dust through air.

    But if I were to stand the battery on top of a metal plate charged by
    a Wimhurst machine it would attract dust, which shows that nothing in
    the battery except its potential with respect to the dust is what
    normally stops it from attracting dust.
    You haven't been following the argument. My claim was that contrary to
    your claim the operating voltages of digital camera sensors are not
    enough to cause dust attracting electrostatic charges. But that's not
    the only way a surface can acquire a static charge, as you yourself
    point out later in this post. Hence the need for static discharge
    measures, even though the operating voltages won't cause electrostatic
    dust attraction problems.
    The verb "pass" is very important there, because of the mechanical
    work involved, as is the amount of resultant charge.
    The numbers matter. While what you say is theoretically true, you need
    a certain dryness of air and strength of "passing" in order to
    generate enough charge to attract dust through air. I think you'd find
    it rather difficult to subject your camera to such conditions :)
    Yes, theoretically in a gravity free vacuum. Not through our everyday
    air. Not only are distances involved, which though small are very
    important, but at the size of a dust particle the hurly burly of
    molecular thermal motion and collision is involved.
    I think our terminology may be too loose here. A static charge is
    simply one that isn't moving. The static charges in CCD sensors are
    for example too low to generate enough electrostatic attraction to
    pull dust through air, and while static, are far from the minimum
    voltages ususally considered necessry to become considered as
    electrostatic charges capable of exerting significant electrostatic
    attraction. Dust attracting electrostatic forces start somewhere with
    effective potential differences in the hundreds of volts.
    I suspected you were the one who was a bit light on electrostatic
    physics! Look up electrostatic induction in Wikipedia. It's important
    and fundamental and quite a different animal from the electromagnetic
    induction which I suspect you're confusing it with.
    Due to the electrostatic induction which you've never heard of that's
    rather difficult to arrange :)
    You're technically correct, but the idea is very difficult to put into
    practice. There have been some static charge reducers which worked on
    that principle by emitting a cloud of charged ions which were selected
    by attraction as needed until attraction vanished because attractive
    charge had been neutralised, but they didn't always have the intended
    effect.
    If that is indeed the case, then you ought to be able to describe to
    me the experiment I can do with flashlight batteries which will show
    ten volts attracting dust particles through air.
    Both. I've built and repaired amplifiers, computers, and electrostatic
    loudspeakers. I've still got at least a thousand dollars worth of
    electronic test gear lying around the house. In the days before
    digital cameras I even built a digital camera using part of a ceramic
    mil-spec dynamic RAM chip with the lid off as the sensor. I was
    playing with this stuff in labs long before you could look up
    miseducated superstitions on the web.
    So you say. But you're the one who boggled at the elementary and
    fundamental concept of electrostatic induction :)
     
    Chris Malcolm, Jan 12, 2008
    #9
  10. Wake up at the back! It's the *lack* of connection I'm trying to
    explain to the brainless popcorn crowd.
    There's a very important difference between the static charges in such
    things as CCD sensors and electrostatic charges of sufficient
    magnitude to attract dust through air, literally orders of magnitude.
    Laws can't deem anything as any English student of any grade could
    tell you. If you actually knew how to apply the laws of the
    conservation of energy in this case you would have realised your
    mistake. Your argument falls on the numbers, which makes it clear
    that your physics is of the numberless armchair verbal variety.
    It is indeed a very important problem, and anyone who understands the
    physics of electrostatic dust attraction and the physics of the
    photon-caused static charges in digital camera image sensors knows
    that you're mixing apples and oranges in supposing that one has
    anything to do with the other.

    If you have any really detailed technical questions as a retard myself
    I'll be glad to put them to folk in the computer and optical research
    labs just down the corridor from my office if the guys in the machine
    vision lab next door can't answer them :)
     
    Chris Malcolm, Jan 12, 2008
    #10
  11. Who said it did?
    Of course not. All that matters is the voltage, not where it comes
    from.
    No, because charges of that voltage migrate to surfaces and
    concentrate on convexities, so being generated locally in the hair
    that's where the thousands of volts stay. But as Tesla's hair-raising
    experiments demostrated, you can if you like -- in appropriate
    conditions -- quite safely raise your entire body to tens of thousands
    of volts above ground potential.
    Of course not. I can't imagine who you're arguing with here. It
    doesn't seem to be anything I've said.
    I was responding to a remark of yours which seemed to imply that the
    low voltages of camera sensor operation were enough to *attract*
    dust. *Attracting* dust through air requires at least some hundreds of
    volts, and it doesn't matter how they're produced. Stroking a cat (or
    your camera) is just as good a way as connecting up to a high voltage
    power supply such as you can find in a CRT based monitor or TV.

    You're now talking not about dust *attraction* but dust
    *adhesion*. There is a huge difference between those two. If the very
    trivial dust adhesion forces (easily broken by a puff of air) is all
    you ever meant to be talking about then forget my argument.
    Considerable care is taken in the engineering of digital cameras and
    their sensors to prevent the problems of electrostatic dust
    *attaction* which do involve hundreds of volts, but if you only meant
    to refer to normal contact adhesion potentials then that's all
    irrelevant.

    Note however that that kind of *adhesion* potential difference between
    dust and the sensor protection surface is low and local enough that it
    has no connection with the electricity involved in sensor operation.
     
    Chris Malcolm, Jan 13, 2008
    #11

  12. ROTFL!

    1. Static charge is measured in Jules, not volts.

    2. Attracting dust through air only requires static charges in the
    millionth of a Jule range.

    3. You, are an idiot.
     
    Cyberiade.it Anonymous Remailer, Jan 13, 2008
    #12
  13. You're quite right, that's how charge is measured. But you won't get
    any attraction without an appropriate potential difference. A very
    large charge at a low potential won't do any attracting.
    Given appropriate potential differences. Maybe the reason you couldn't
    look this up on the web to check it out properly is because you can't
    spell it :)
    It's such a relief to be able to say that in a newsgroup when you
    never get any opportunities in real life, isn't it? :)
     
    Chris Malcolm, Jan 14, 2008
    #13
  14. I'm actually very good at reading and learning. It's one of the
    professional skills which I've been employed to teach postgrad
    students.

    I suspect that what's confusing you is that I'm not learning anything
    from your particular posts. There's a number of possible explanations
    for that observation :)
     
    Chris Malcolm, Jan 14, 2008
    #14
  15. Guest

    Dave Guest

    Sorry but charge is measures in Coulombs.

    Joules (note the correct spelling) is the SI measurement for energy. At
    least this was the case when I studied physics at Cambridge University.

    As you say...ROTFL. :)
     
    Dave, Jan 14, 2008
    #15
  16. Guest

    Dave Guest

    No problem, ???????.
     
    Dave, Jan 14, 2008
    #16
  17. Guest

    Guest Guest

    In message

    Energy measured in Joules

    Charge measured in coulombs
     
    Guest, Jan 14, 2008
    #17
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