Long exposures are noisy

Discussion in 'Digital SLR' started by D.M. Procida, Aug 1, 2007.

  1. D.M. Procida

    D.M. Procida Guest

    The pictures themselves are great - but the camera (Pentax K100D) makes
    an absolute racket.

    There's a bit of noise during the exposure itself, but afterwards, while
    I presume the camera is processing it, it sings and coughs to itself at
    length. Is this normal?

    Also, it seems to take the camera as long to process a 30-second
    exposure as it does to take the picture itself (i.e. before the camera
    is ready for further action). Why should this be the case?

    D.M. Procida, Aug 1, 2007
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  2. D.M. Procida

    John Bean Guest

    IS on or off?
    Automatic "dark frame subtraction". You can Google the
    phrase for explanations.
    John Bean, Aug 1, 2007
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  3. Also, it seems to take the camera as long to process a 30-second
    This is the noise reduction feature (image noise, not audible noise)
    that kicks in for long exposures. You can turn it off if you like,
    either via the setup or custom menu.

    Marc Sabatella

    Music, art, & educational materials
    Featuring "A Jazz Improvisation Primer"
    Marc Sabatella, Aug 1, 2007
  4. D.M. Procida

    DoN. Nichols Guest

    Well ... based on the Nikon D70, the default mode for long
    exposures is "Long exp. NR" mode, which takes a second "non" picture with the same
    exposure time as the actual exposure, but with the shutter closed. This
    gives the camera a reference for the noise patterns for that length of
    exposure at the temperature at which the camera is being used. This is
    then subtracted digitally from the actual image, making for a much
    better image than if you turn the NR mode off (which I do when shooting
    fireworks, since I am more willing to live with the noise than to lose
    the ability to take another shot right away.

    Your camera may also offer a way to turn off the NR mode
    (whatever they call it), and you should experiment with shooting two
    long-exposure shots (one with and one without) just to show you what the
    difference in appearance is, so you can know when you can live with the
    noise as a tradeoff for the ability to shoot another exposure soon after
    the first.

    DoN. Nichols, Aug 2, 2007
  5. D.M. Procida

    Ray Macey Guest

    It's more hot pixel reduction than noise reduction...

    Ray Macey, Aug 2, 2007
  6. D.M. Procida

    Pete D Guest

    And is called dark frame subtraction.
    Pete D, Aug 3, 2007
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