Canon 20D / dirty sensor / small circles within image / wait 1min to change lenses ???

Discussion in 'Canon' started by MJL Photo, Jun 3, 2005.

  1. MJL Photo

    MJL Photo Guest

    SITUATION:
    There is small circles with a pin point in the centre of each appearing
    within all images taken.
    Could this be a sign of a dirty sensor?

    RECOMMENDED:
    This friend of mine (i am still using film) uses the 20D and was told by the
    shop owner to wait 60 seconds after taking a photo before changing lenses.
    The reasoning behind this was that the sensor still holds a (possible
    electro magnetic) charge for a short time after taking a photo.
    Could removing the lens directly after the shutter allow dust particles to
    enter and adhere to the sensor?

    If this is truely the recommended way of changing lenses, I think I will
    stick with film until snesor cleaning is more user-friendly.

    This all sounds very odd, but is it possible???

    Any comments?
     
    MJL Photo, Jun 3, 2005
    #1
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  2. MJL Photo

    SimonLW Guest

    Yes, that static charge created by the sensor stuff I keep hearing about is
    utter nonsense. Only very low logic level voltages are used on the CCD. It
    is nothing like the old camera tubes that have a few thousand volts on the
    anode. The dust lands on the sensor as it does other surfaces like the
    mirror or the side of the mirror box. The less time the mirror box is open
    (no lens attached) the better the chances for dust entry. Changing lenses
    outside on a windy day is likely going to get some dust inside. Some Olympus
    cameras us ultrasonics to vibrate the dust off the sensor. I don't know how
    effective it is.
    -S
     
    SimonLW, Jun 3, 2005
    #2
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  3. MJL Photo

    SimonLW Guest

    Yes, that static charge created by the sensor stuff I keep hearing about is
    utter nonsense. Only very low logic level voltages are used on the CCD. It
    is nothing like the old camera tubes that have a few thousand volts on the
    anode. The dust lands on the sensor as it does other surfaces like the
    mirror or the side of the mirror box. The less time the mirror box is open
    (no lens attached) the better the chances for dust entry. Changing lenses
    outside on a windy day is likely going to get some dust inside. Some Olympus
    cameras us ultrasonics to vibrate the dust off the sensor. I don't know how
    effective it is.
    -S
     
    SimonLW, Jun 3, 2005
    #3
  4. MJL Photo

    Mike Guest

    Sensor dust is pretty much a fact of life if you want to use a digital SLR
    (and many non-SLRs as well). However, it would be a ridiculous reason for
    anyone to stick with film (there are plenty of *good* reasons to do so, this
    is not one). Being very fussy about lens changes will help, but you'll get a
    dust speck one day. When you do, there're plenty of products on the market
    to help you (some are much better than others, and all need to be used with
    plenty of care so do your research.) And at the end of the day, if you've
    got a couple of specks on an important image (which, by the way, usually
    only show up in low-detail areas and on images taken with the lens almost
    wide-open) then the healing and clone brushes in Photoshop are your
    friends - nobody will ever know!!

    Cheers, from somebody who *used* to sweat about sensor dust.
     
    Mike, Jun 4, 2005
    #4
  5. MJL Photo

    Skip M Guest

    This may seem like a silly question, but since the sensor is behind the
    shutter, how does dust get to it? If the sensor were that permeable to
    dust, a) wouldn't it be permeable to light, and b) wouldn't we have had dust
    problems with film, too?
    I've wondered this for some time, now...
     
    Skip M, Jun 4, 2005
    #5
  6. MJL Photo

    Skip M Guest

    Then changing a lens wouldn't make any difference, would it? I mean, if the
    shutter is closed when you change lenses, how is changing lenses responsible
    for dust getting in? And if there is a lens mounted, and dust still gets
    in, why is everyon so careful when changing lenses?
    I never had dust get on film in camera, just in the lab. Of course, that
    little fuzzy strip on the canister probably did an admirable job of keeping
    the dust out, now that I think of it...
     
    Skip M, Jun 4, 2005
    #6
  7. SNIP
    In a dSLR, as the mirror swings out of the optical path it creates
    turbulation, and as a result all dust in the mirror chamber gets a
    chance to move to the sensor as the shutter opens (and a fast moving
    shutter curtain will reduce local pressure and suck in dust).

    Bart
     
    Bart van der Wolf, Jun 5, 2005
    #7
  8. MJL Photo

    Skip M Guest

    Ah....
     
    Skip M, Jun 5, 2005
    #8
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