Re: Detecting dust on a DSLR sensor

Discussion in 'Digital Photography' started by David J Taylor, Jun 28, 2008.

  1. Alfred Molon wrote:
    > I heard of a technique - take a photo at the smallest aperture (F22 or
    > higher) - but I don't know if it works. What is the best way to detect
    > dust, short of opening the camera and inspecting the image sensor?


    Yes, it works, and it may often be the first way you detect dust! I have
    found that a clear blue sky is quite sensitive to dust spots.

    David
    David J Taylor, Jun 28, 2008
    #1
    1. Advertising

  2. Alfred Molon wrote:
    > In article <g45i2h$8on$>, says...
    >
    >> Or a white sheet of paper that is very very out of focus. This means,
    >> at f/22 or greater, like the lens (preferably a tele) is focused at
    >> infinity and the paper is two inches from the lens. Be sure it comes
    >> out gray, not white.

    >
    > Just a question or two - why do you need to set the camera to such a
    > small aperture and why is dust less visible at larger apertures?


    You need to create, as near as possible, a pinhole lens. This is so that
    the divergence of the rays between the dust and the focal plane is
    minimised.

    David
    David J Taylor, Jun 28, 2008
    #2
    1. Advertising

  3. David J Taylor

    Paul Furman Guest

    lid wrote:
    > Alfred Molon wrote:
    >> In article <g45i2h$8on$>, says...
    >>
    >>> Or a white sheet of paper that is very very out of focus. This means,
    >>> at f/22 or greater, like the lens (preferably a tele) is focused at
    >>> infinity and the paper is two inches from the lens. Be sure it comes
    >>> out gray, not white.

    >>
    >> Just a question or two - why do you need to set the camera to such a
    >> small aperture and why is dust less visible at larger apertures?

    >
    > An actual INTERESTING question, with a real answer available!
    >
    > The dust is not on the sensor. Its on the glass in front of
    > the sensor, well in front. If you use a wide-open lens,
    > a large cone of light comes into each pixel on the sensor.
    > Most of that light from the big cone will miss the spot of dust.
    >
    > But if you use f/22 or even better f/32 or f/45, etc. only a
    > tiny pencil of light will come from the lens to each pixel. A
    > tiny dust spot will block a large fraction of that light.
    >
    >
    > This would not apply to a spot of dust sitting right on the
    > surface of film, for example. I should add that it also does apply
    > to dust, spots, and even scratches on the front of your lens. A
    > large numerical f/number makes such spots more obvious.


    And strangely, very small f-number lenses with a point source of light
    out of focus will also work like a pinhole focusing dust specs inside
    the lens and on the sensor.

    --
    Paul Furman
    www.edgehill.net
    www.baynatives.com

    all google groups messages filtered due to spam
    Paul Furman, Jun 28, 2008
    #3
  4. David J Taylor

    nospam Guest

    In article <>, Alfred
    Molon <> wrote:

    > In article <g4627q$dbb$>, says...
    >
    > > The dust is not on the sensor. Its on the glass in front of
    > > the sensor, well in front.

    >
    > Why do then manufacturers recommend not to use a brush to remove the
    > dust giving as a reason that the sensor might be scratched?


    they mean the glass can be scratched.
    nospam, Jun 29, 2008
    #4
  5. David J Taylor

    Paul Furman Guest

    nospam wrote:
    > In article <>, Alfred
    > Molon <> wrote:
    >
    >> In article <g4627q$dbb$>, says...
    >>
    >>> The dust is not on the sensor. Its on the glass in front of
    >>> the sensor, well in front.

    >> Why do then manufacturers recommend not to use a brush to remove the
    >> dust giving as a reason that the sensor might be scratched?

    >
    > they mean the glass can be scratched.


    And I think they exaggerate the danger. A wet cleaning seems just as
    likely to drag a spec of diamond dust across the glass as a clean dry
    nylon brush.

    --
    Paul Furman
    www.edgehill.net
    www.baynatives.com

    all google groups messages filtered due to spam
    Paul Furman, Jun 29, 2008
    #5
    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. Bay Area Dave
    Replies:
    7
    Views:
    371
    Paul Cordes
    Sep 21, 2003
  2. DVD Verdict
    Replies:
    0
    Views:
    486
    DVD Verdict
    Feb 26, 2004
  3. MeMe

    Dust on sensor, Sensor Brush = hogwash solution?

    MeMe, Feb 10, 2005, in forum: Digital Photography
    Replies:
    29
    Views:
    1,092
  4. embee

    Dust detecting software

    embee, Oct 2, 2006, in forum: Digital Photography
    Replies:
    25
    Views:
    704
    ASAAR
    Oct 7, 2006
  5. Replies:
    14
    Views:
    2,010
Loading...

Share This Page