Strange dirt problem

Discussion in 'Digital SLR' started by google.20.jbloggs, May 22, 2005.

  1. I have a D70, about 2 weeks old.

    At very high f-stops, there are 5 or 6 dirt specks on the images, which
    become blurred at lower f-stops. (specks are always in the same place)
    Replacing the lens made no difference, but there is no obvious dirt on
    the sensor, and taking a shot with no lens gives no dirt. Also, if the
    dirt were on the sensor, it would look the same no matter what the
    f-stop, right?

    So it's not the body, and it's not the lens...

    Any ideas???
     
    google.20.jbloggs, May 22, 2005
    #1
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  2. google.20.jbloggs

    DoN. Nichols Guest

    Numerically lower -- as in larger opening?
    The dust on the lens *can't* form an image on the sensor -- it
    is way out of focus, so changing the lens won't do anything for this.
    It is on top of two filters above the sensor, so it is far
    enough away that anything but a very narrow beam of light will reach
    individual pixels through multiple paths -- most missing the dust
    particles. Only when your lens is stopped way down does the light form
    a narrow enough cone that the dust particles do the damage to the image.
    It *is* the sensor. You need to clean it.

    Note that the image is inverted on the sensor, so what may
    appear to be in the upper-right-hand corner of the image will be on the
    lower-left-hand corner of the sensor.

    And it doesn't take a very big bit of dust to show up as
    blocking one or two pixels. You might not be able to see them on the
    sensor without a good long-focus microscope (the stereo-zoom one by
    either B&L or AO would be excellent for this purpose -- but you don't
    need to *see* it to remove it.

    First try a bulb blower -- which may be sufficient for the
    purpose. (The ones sold for cleaning out earwax at the drugstore are
    a nice size -- but use a *new* one for the purpose, not one which has
    already been used for its intended purpose.)

    If that does not work, you may need to get the kit with the
    "eclipse" (alcohol) and the "pec pads" (lint-free cloth around a
    specially made flexible plastic holder. Hopefully, someone else will
    remember the URL which describes (and offers) these products.

    You *could* take it back to Nikon for cleaning -- but it will
    acquire more as you change lenses, so it makes more sense to learn to do
    it yourself, so you won't be without the camera for several days each
    time.

    Best of luck,
    DoN.
     
    DoN. Nichols, May 22, 2005
    #2
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  3. google.20.jbloggs

    Frederick Guest

    DoN. Nichols wrote:

    I agree with you 100%
    The URL is probably this one:
    http://www.pbase.com/copperhill/ccd_cleaning

    I use his method, but use high purity isopropyl alcohol, not eclipse. I
    think eclipse is high purity methanol at a very high price. Methanol
    will evaporate a little faster. Isopropynol evaporates fast enough from
    my experience.

    I made my own "wand" using a piece of plastic kitchen spatula, cut to
    14mm wide, shaped as described on the above site, and clamped firmly in
    the tongs of a stylus knife handle so that I can hold it very easily
    without it rotating in my fingers.
    Results of the two cleans I needed were 100% first time.

    I practised my technique using a microscope slide before tyring the real
    thing. I think that was a good idea.
     
    Frederick, May 22, 2005
    #3
  4. google.20.jbloggs

    Cynicor Guest

    Er...by the way, can anyone tell me how to get earwax off the sensor of
    my D70? Thanks.
     
    Cynicor, May 22, 2005
    #4
  5. google.20.jbloggs

    Alan Browne Guest

    dust specs on the sensor cover. At higher f/ the 'cone' of light is
    narrow and so the spots get silhouetted. At lower f/ the cone is wide
    and light gets 'under' the dust. Note that the dust is on the cover of
    the sensor so at wide aperture there is room for the light to get around
    the spec.

    See your manual for instructions on using an ear syringe or similar to
    blow off the dust w/o touching the sensor cover.

    Cheers,
    Alan.
     
    Alan Browne, May 22, 2005
    #5
  6. What do people think about using the high pressure air canisters sold
    for cleaning keyboards, etc.? Too violent?
     
    google.20.jbloggs, May 22, 2005
    #6
  7. google.20.jbloggs

    Bubbabob Guest

    Let's just say that it would be an act of supreme idiocy.
     
    Bubbabob, May 22, 2005
    #7
  8. google.20.jbloggs

    Frederick Guest

    Yes. Don't use them on your camera. Use them on your keyboard etc.
     
    Frederick, May 22, 2005
    #8
  9. well, I just used a foot pump for blowing up air mattresses with
    perfect results - thank you all for your help.
     
    google.20.jbloggs, May 23, 2005
    #9
  10. google.20.jbloggs

    Zed Pobre Guest

    Not only are they too violent, but they may become too cold, and most
    cannisters contain components that will actually add sticky dirt to
    the sensor and make the situation worse. Do not attempt this.
     
    Zed Pobre, May 23, 2005
    #10
  11. google.20.jbloggs

    Frederick Guest

    Okay - I suggest that probably wasn't a great idea, but you got away
    with it. Pumps with rubber components, and the air mattresses
    themselves are likely to have lots of powders that are used as
    anti-blocking (to stop the surface sticking to itself) and anti-oxidants
    floating around in liberal quantities. (Talc, Zinc Stearate, etc) The
    right pump, with good clean hoses, and never used to inflate a real
    rubber lined air mattress might be okay.
     
    Frederick, May 23, 2005
    #11
  12. google.20.jbloggs

    Cynicor Guest

    Cool, but what are you going to use for your camera sensor? :D
     
    Cynicor, May 23, 2005
    #12
  13. good point - so should I get one of those little brush-blowers (and use
    it without the brush on)?
     
    google.20.jbloggs, May 23, 2005
    #13
  14. google.20.jbloggs

    Cynicor Guest

    Cynicor, May 23, 2005
    #14
  15. google.20.jbloggs

    r Guest

    Maybe a lima bean or two?
     
    r, May 23, 2005
    #15
  16. google.20.jbloggs

    Gaderian Guest

    The propellant in high pressure air canisters contains an inert gas that
    will leave a slight film (pardon the pun) on your CCD. Not good.
     
    Gaderian, May 23, 2005
    #16
  17. google.20.jbloggs

    DoN. Nichols Guest

    It depends on the type of canister. I've got some made by
    Leland Co. "Power Clean" which works from screw-in CO2 cartridges. The
    aperture at the end of the nozzle is quite small, so at any reasonable
    distance, the airflow is quite reasonable. However, if you hold it so
    the cartridge is above the valve, you will get liquid CO2, which will
    freeze the surface which it hits. When it evaporates (very quickly), it
    will leave nothing behind, but the thermal shock -- especially to
    a silicon device as large as the sensor, could cause significant damage.

    Enjoy,
    DoN.
     
    DoN. Nichols, May 23, 2005
    #17
  18. google.20.jbloggs

    Bubbabob Guest

    When the sensor freezes, it's freezing water vapor out of the air onto
    the sensor. This is not usually pure water and when the ice sublimates
    it leaves behind dissolved salts and minerals.
     
    Bubbabob, May 23, 2005
    #18
  19. google.20.jbloggs

    Sonrise Guest

    The latest issue of Photoshop User has an article that recommends a
    variation with compresed air. The author states that a blast of compressed
    air across the tip of a fine bristle brush will provide enough electrostatic
    charge to attract dust from the sensor when brushed lightly. Seems much
    simpler than wiping the sensor filter.

    Has anyone else tried this technique, and is there risk that the static
    charge could damage the sensor? I ask because I need to clean my 20D.

    Sonrise
     
    Sonrise, May 23, 2005
    #19
  20. google.20.jbloggs

    Alan Browne Guest

    Do not aim inside your camera. The blast is strong enough to cause
    mechanical damage (mirror assembly, shutter blades, etc.).

    If you do use such canned air:

    1) point away from anything valuable, give a couple short blasts to
    clear propellant.

    2) Always hold the can vertical to prevent propellant from getting into
    to the works and out onto any surfaces.

    I use canned air to blow off film before scanning, but always with the
    two points above observed. I'd never point it at equipment.

    Cheers,
    Alan
     
    Alan Browne, May 23, 2005
    #20
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