purpose of increasing ISO?

Discussion in 'Photography' started by Mr.Bolshoyhuy, Feb 17, 2006.

  1. I am confused as to why a high ISO is needed at all.
    ISO800 is grainier than ISO100.
    When shooting stationary objects in low light, why use it instead of
    increasing exposure compensation, or decreasing the shutter speed
    Is it better to shoot at 4sec/ISO100 than 1/4sec ISO400?

    The shutter speed is increased with higher ISO; thus
    making it useful only for action shots only.
    Mr.Bolshoyhuy, Feb 17, 2006
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  2. Mr.Bolshoyhuy

    Beach Bum Guest

    Longer exposure on digital camera also creates noise. I've never
    experimented to see if long exposure vs. higher ISO is noiser (assuming in
    camera noise removal is turned off).

    You might want to hand hold your camera in low light - a high ISO comes in
    handy here too. BTW, low light doesn't have to mean dark - it might just
    mean indoors under tungston lighting.
    Beach Bum, Feb 17, 2006
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  3. Mr.Bolshoyhuy

    Whiskers Guest

    To accomodate circumstances that are outside the range of adjustments
    available with aperture and shutter-speed. Or to achieve particular
    aperture and shutter-speed with the available light. Or perhaps the
    photographer wants the 'noisiness' or 'grain' (or lack of it) or relative
    colour balances or saturation of a particular ISO setting on a particular
    A reasonable assumption.
    Exposure compensation isn't for that; it's to make a photograph 'lighter'
    or 'darker' than the camera wants to make it - if you tell the camera to
    use "-1 stop compensation" it will possibly use a faster shutter speed (or
    possibly a smaller aperture), but the photograph will be 'darker' - with
    less detail in the shadows, perhaps none at all, and perhaps with no real

    It is certainly possible to get a 'correct' exposure by adjusting the
    shutter, aperture, and ISO, settings - in accordance with the 'reciprocity
    rule'; so yes, instead of using a higher ISO you could use a slower
    shutter speed - but that often creates more 'noise' in a digital image,
    and the longer the exposure the more chance there is of camera movement
    introducing unwanted blur - no camera support is wholly immune to
    vibration, although a really secure fixing to bedrock is pretty good.
    (Image stabilisers are not infallible either; some can even make things
    worse in some circumstances).
    Unless you change the aperture settings as well, one or the other of those
    will be 'wrong'; the equivalent shutter speed at ISO 400 would have to be
    1 second, not 1/4 second, to get equivalent 'brightness' in the two
    No; you could keep the same shutter speed but use a smaller aperture, to
    get greater 'depth of field'. Depth of field is already pretty extensive
    on a digital compact anyway, thanks to the small image sensor used, but the
    aperture can still be significant in 'close-ups' or when 'zoomed in'.
    Whiskers, Feb 17, 2006
  4. You've restricted yourself to "stationary objects", but many
    good photographs are of non-stationary objects. That would then
    require higher ISO because slower shutter speeds are not usable.
    Assuming all other things are equal, it makes no difference.

    However, all things are *never* equal, and the balancing act
    required to choose is what makes one person an artist with a
    camera, another person a technician, and a third person can only
    take snapshots.

    At ISO 400 there will be more noise. How much more depends on
    which camera. How much difference the noise makes depends on
    the scene (a high key scene with low contrast might not be bad;
    a low key scene with high contrast might be really ugly; and
    either might be okay if the grain pattern just happens to be

    The type and character of the noise might be very different too,
    between a 1/4 second and a 4 second exposure. (Probably not
    significant at ISO 100, but that might apply to the difference
    between shooting at ISO 400 and ISO 1600.)

    At 1/4 second the stability requirements for the camera and
    lense are different than at 4 seconds. Vibration from mirror
    slap might show up at 1/4 second, and not at 4 seconds.

    Obviously some of the manipulations are merely technical, while
    some might be artistic or technical...
    Restate that: it might be required only for actions shots.
    Floyd Davidson, Feb 17, 2006
  5. Mr.Bolshoyhuy

    Rutger Guest

    If you want a very narrow DOF at low light, you need a high sensitivity
    setting to get a wide opening.

    Rutger, Feb 18, 2006
  6. Well, one reason why you use a faster ISO is so that you can possibly
    take a picture that you couldn't with a slower ISO. ISO 800 is 3 stops
    faster than 100, so you can get away 3 stops slower shutter speed. Instead
    of having to shoot at 1/30, you can shoot at 1/250. Better to deal with the
    noise than the blur. Plug-ins like Noise Ninja can do a pretty darned good
    job of reducing noise.
    William Oertell, Feb 18, 2006
  7. Four times better -- or four times worse, depending on the
    definition of "better" :)

    Now, if you asked 1sec at ISO400, then it would be the same :)

    Carlos Moreno, Feb 18, 2006
  8. Mr.Bolshoyhuy

    editor Guest

    Higher shutter speed - VERY important if the subjects can't (or
    won't) stay still for the photo! (Things like sports, animals,
    crowds.) Ability to take indoor photos without flash and distraction -
    and without range limits of flash; the ability to avoid range limits of
    flash is very important for some news, indoor sports, and education
    photos. Cancels out hand shake.

    No $4 to park! No $6 admission! http://www.INTERNET-GUN-SHOW.com
    editor, Feb 18, 2006
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