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

Discussion in 'Digital Photography' 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
    1. Advertising

  2. MJL Photo

    SimonLW Guest

    "MJL Photo" <> wrote in message
    news:bgTne.1556107$8l.842610@pd7tw1no...
    > 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?
    >
    >

    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
    1. Advertising

  3. MJL Photo

    SimonLW Guest

    "MJL Photo" <> wrote in message
    news:bgTne.1556107$8l.842610@pd7tw1no...
    > 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?
    >
    >

    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

    Alfred Molon Guest

    In article <bgTne.1556107$8l.842610@pd7tw1no>, MJL Photo says...
    > 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.


    Well, there is the Olympus E300 DSLR which every time you switch on the
    camera automatically cleans the CCD (inbuilt supersonic wave cleaner).
    --

    Alfred Molon
    ------------------------------
    Olympus 4040, 5050, 5060, 7070, 8080, E300 forum at
    http://groups.yahoo.com/group/MyOlympus/
    Olympus 8080 resource - http://myolympus.org/8080/
    Alfred Molon, Jun 3, 2005
    #4
  5. MJL Photo

    Jim Townsend Guest

    SimonLW wrote:


    > 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.


    Yes... It's no more than 5 volts on the CMOS sensor in the
    20D.. Probably around 2 or 3.

    Not only that, but the sensor is behind a mirror AND completely
    covered by the shutter. (The shutter stays closed over the
    sensor until it's time to take an exposure, or the sensor
    cleaning function has been activated).

    With the mirror AND shutter in the way, dust would have a tough
    time finding the sensor.
    Jim Townsend, Jun 4, 2005
    #5
  6. "With the mirror AND shutter in the way, dust would have a tough
    time finding the sensor. "

    It gets there, though. Doesn't seem to have a hard time at all. Even
    if you keep your lens changes short, and are fastidious about where you
    do the changes.

    OTOH, I haven't yet seen dust that wasn't easily abated by blowing it
    with a bulb blower.
    James Of Tucson, Jun 4, 2005
    #6
  7. MJL Photo

    Mike Guest

    "MJL Photo" <> wrote in message
    news:bgTne.1556107$8l.842610@pd7tw1no...
    > 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?
    >

    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
    #7
  8. MJL Photo

    Skip M Guest

    "SimonLW" <> wrote in message
    news:42a07ab1$...
    > "MJL Photo" <> wrote in message
    > news:bgTne.1556107$8l.842610@pd7tw1no...
    >> 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?
    >>
    >>

    > 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
    >
    >

    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 Middleton
    http://www.shadowcatcherimagery.com
    Skip M, Jun 4, 2005
    #8
  9. >since the sensor is behind the
    >shutter, how does dust get to it?


    I suppose it wouldn't, if you never opened the shutter.

    >b) wouldn't we have had dust
    >problems with film, too?


    We do! But the dust travels with the film, instead of staying put.
    James Of Tucson, Jun 4, 2005
    #9
  10. MJL Photo

    Skip M Guest

    "James Of Tucson" <> wrote in message
    news:...
    > >since the sensor is behind the
    >>shutter, how does dust get to it?

    >
    > I suppose it wouldn't, if you never opened the shutter.


    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?

    >
    >>b) wouldn't we have had dust
    >>problems with film, too?

    >
    > We do! But the dust travels with the film, instead of staying put.
    >

    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 Middleton
    http://www.shadowcatcherimagery.com
    Skip M, Jun 4, 2005
    #10
  11. "Skip M" <> wrote in message
    news:kijoe.365$Cr.285@fed1read07...
    SNIP
    > This may seem like a silly question, but since the sensor is behind
    > the shutter, how does dust get to it?


    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
    #11
  12. MJL Photo

    Skip M Guest

    "Bart van der Wolf" <> wrote in message
    news:42a24188$0$29628$4all.nl...
    >
    > "Skip M" <> wrote in message
    > news:kijoe.365$Cr.285@fed1read07...
    > SNIP
    >> This may seem like a silly question, but since the sensor is behind the
    >> shutter, how does dust get to it?

    >
    > 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


    Ah....

    --
    Skip Middleton
    http://www.shadowcatcherimagery.com
    Skip M, Jun 5, 2005
    #12
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. Chris
    Replies:
    1
    Views:
    658
    joevan
    May 24, 2004
  2. measekite

    Full Frame Lenses vs Small Sensor Lenses

    measekite, Sep 11, 2006, in forum: Digital Photography
    Replies:
    15
    Views:
    640
    Mueen Nawaz
    Sep 13, 2006
  3. David J Taylor
    Replies:
    4
    Views:
    790
    Anoni Moose
    Aug 15, 2007
  4. Gopi
    Replies:
    1
    Views:
    487
    Abhijit
    Sep 7, 2007
  5. measekite

    Big Sensor FX vs Small Sensor DX - No Diff?

    measekite, Sep 21, 2008, in forum: Digital Photography
    Replies:
    11
    Views:
    1,007
    Böwser
    Sep 22, 2008
Loading...

Share This Page