Does ISO really mean much in a digital context?

Discussion in 'Digital Cameras' started by Paul Ciszek, Jun 6, 2012.

  1. Paul Ciszek

    Paul Ciszek Guest

    I see that the Olympus OM-D E-M5 doesn't have an ISO mode lower than
    200. What does ISO really mean for a digital camera, though?
    Paul Ciszek, Jun 6, 2012
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  2. Paul Ciszek

    Alan Browne Guest

    But it certainly has quite a bit above 200.

    First off it is part and parcel of the reciprocity equation that
    photographers use when trading between DOF, speed and image quality. It
    used to be 2 degrees of freedom - now there are three (shutter speed,
    aperture and now ISO).

    The other important notion is: gain.

    The 'typical' or 'natural' ISO of most digital cameras is about 150 -
    200. So going below that means artificial compression of the dynamic range.

    Above that, at least for a bit, analog amplification, means no big loss
    in DR to increase the gain, but increasing noise. But as the noise is
    constrained spatially (no big "grain blobs") it looks a lot better than
    high speed film.

    Later DSLR's are truly remarkable in the high ISO's achieved with little
    noise. That means shooting in more difficult conditions where film was
    challenged while getting high quality images without needing a tripod.
    (Add in image stabilization and it's compounded by another 2 - 4 stops).

    When you run out of analog gain (why do they call them digital cameras
    anyway?) then digital gain is applied for the higher end.

    And as A/D depth increases the gains (so to speak) in ISO may rise some

    If you need "lower than 200" ISO you can get some very expensive digital
    cameras (Hasselblad comes to mind) or throw on an ND filter.

    I'm sure others will have more to add.
    Alan Browne, Jun 7, 2012
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  3. Paul Ciszek

    Whisky-dave Guest

    There was always 3 wasn;t there. I remmeber buying HP3 because it was
    400 ASA/ISO
    I wanted to photograph the stars so reciprocity was a slight concern
    to me.
    DOF wasn;t relivant but shutter speed was.

    In the days of film a lower ASA/ISO meant finer grain and usually less
    contrasty images.

    Not sure how the modern DSLR is arrcted by setting a low ISO, btu I
    still assume a lower
    ISO setting is linked to better image quality than a higher ISO could
    produce given the same conditions.
    Whisky-dave, Jun 7, 2012
  4. Paul Ciszek

    Paul Ciszek Guest

    Sigh. I've just been so conditioned to the idea that you *must* use
    ISO 100 for bright, sunny outdoor photography. Heck, maybe I should
    just set ISO to "Auto" and think of it no more. :-(
    Paul Ciszek, Jun 7, 2012
  5. Nikon, maybe. Canon, not so much.

    Wolfgang Weisselberg, Jun 7, 2012
  6. Depends on the specific sensor and how the camera maker has handled
    the lowest ISOs in a particular camera. ISO 50 is often handled as
    Alan suggests, being "bodged" in simply to give you more latitude in
    shutter and aperture selection, but not in all cases. For example,
    according to DXO's tests, the Sony A77 has it's top dynamic range and
    least noise at ISO 50.
    Chris Malcolm, Jun 8, 2012
  7. Canon usually has the native ISO between 50 and 100, as in "50
    does cost dynamic range in the highlights (and is therefore an
    extended ISO setting" and "100 doesn't". Which sorta bites
    the "150-200" claim.

    Nikon, AFAIK, usually start their normal range at 200 ... so
    there the claim may work out.

    Wolfgang Weisselberg, Jun 8, 2012
  8. The Sony R1 had its base ISO at 160, which was where it was at its
    best. The next up was 200, then 400, etc..

    I get the impression the camera makers know what the best ISO for
    their sensor is, but they also know the howls of protest and confusion
    and ignorant criticism and salesdriod superstition that would
    inevitably follow releasing a camera with a base ISO of say 87 or
    163. So they simply stick to the old film-based ISO steps so as not to
    alarm the collective brain of the market.
    Chris Malcolm, Jun 10, 2012
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