someone please explain ISO and exposure

Discussion in 'Digital Photography' started by Martin Lynch, Oct 10, 2004.

  1. Martin Lynch

    Martin Lynch Guest

    Can someone please explain how adjusting the ISO and Exposure settings
    on my digital camera will affect my pictures?

    By the way, is ISO the same thing as "shutter speed"? My camera's ISO
    ranges from, I think 100 to 400. Is 400 considered the "fast" speed?

    If I'm correct, FAST shutter speed is used for action shots. But
    would you also say that SLOW shutter speed could be used to compensate
    for poor lighting?

    As for exposure, my camera ranges from -2 to +2. Which setting is for
    taking pictures in the dark with no flash? It seems to me that
    "exposure" would be synonymous with "shutter speed/ISO" but maybe I'm
    just confused.

    A novice photographer
    Martin Lynch, Oct 10, 2004
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  2. Take a look at
    which has an explanation for ISO as it relates to film. In digital cameras,
    the thought is the same.

    It is not the same as shutter speed. I shoot with manual cameras a lot, so
    from my point of view here's an explanation. If I have a film rated ISO 50,
    and my exposure meter says I can shoot at 1/60 of a second at f/16, then I
    can vary the shutter speed and aperture and maintain the same amount of
    light hitting the film: 1/30 at f/32 or 1/120 at f/8. If my film speed is
    ISO 100, I can get the equivalent exposure to ISO 50 with half the
    light. So 1/120 at f/16, say, instead of 1/60 at f/16.
    It's a judgment. You may want to use fast shutter speed to freeze action,
    but you may also want a slow shutter speed to blur the action, which may
    create an artistic representation of speed. Look at
    for an example.

    If the light is really low, you may be left with no choice but a wide
    aperture and slow shutter speed. You could try setting your digital camera
    to a higher ISO to compensate. There may be in increase in noise with ISO
    400. Try it and see. Cameras vary in the amount of noise.
    Yeah, you're just confused. The manual which came with your camera will
    explain what the -2 to +2 means. It's probably a way of adjusting the
    exposure so that it comes out more nearly to what you expect. I would not
    use that adjustment to try to get photos in the dark with no flash. Since
    you're shooting digital, let me make a suggestion: try all this stuff and
    then look at the resulting images on your computer to see how it turns
    Phil Stripling, Oct 10, 2004
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  3. Martin Lynch

    Bob Guest

    ISO is the SENSITIVITY of the camera. A high ISO can get more light, so it helps
    in the dark or with fast exposures of sports, but it increases noise. ISO 400
    will give a very 'grainy' picture, no good for quality prints.
    it's the most sensitive setting, and the noisiest.
    yes... but you can get blur if you move the camera during the shot.
    Since you didn't give a qualifier, -2 or +2 doesn't tell me much! It may be the
    compensation if the picture is too dark or light. If you think the picture was
    too dark, go to plus 1 and shoot again...
    'exposure' generally means the combination of all things. High shutter speed and
    high ISO can give the same exposure as low ISO and low shutter speed.

    'exposure' used to refer to how the film was exposed... long time or short, big
    lens or small.
    Bob, Oct 10, 2004
  4. Martin Lynch

    GT40 Guest

    The higher the ISO number the less light you need at the same exposure
    (same shutter and apature setting)

    No, ISO is a mesure of how sensative the image recording metod is
    (film or digital camera sensor) to light. 400 is an medium speed, 800
    and up is fast, some cameras can go to 3200, mine goes to 1600.
    Fast shutter speeds feeze motion, slow ones blur it. How you use it
    depends on your personal style
    GT40, Oct 10, 2004
  5. I'd add a little further note here. IF you push the speed- that is,
    set the ISO higher than standard, then yes you would get more noise.
    However, if the camera already has a higher ISO value, then you would
    not necessarily get more noise.

    However, the ISO of a silicon CCD chip is pretty well fixed by the
    materials and processes. Most of them are ISO 100. If it is a
    different chip technology, on the other hand, then it CAN have a
    different ISO. In that case, if it has a higher sensitivity it can
    get it without a greater noise. Lets hope the chip manufacturers can
    indeed find ways to create faster chips. Hard, as I say, but that is
    one area where film is better than digital currently. There are lots
    of really great 400 films, and even a few 800 films are pretty good.
    Don Stauffer in Minneapolis, Oct 10, 2004
  6. Martin Lynch

    Bob Guest

    Noise is related to the actual size of the sensor, so that large (not
    pixel-number large but physical-size large) sensors are quieter.

    I often shoot with my D70 set to ISO 1000 with no real noise problem. And it
    beats any color film I could ever afford!

    If sensor technology is anything like solid state technology, it's just a matter
    of time before the sensors become quieter. Look at today's transistors compared
    to the ones made in the 60s. A stereo back then was quite noisy with a S/N ratio
    of barely 50db, now 95db is common. Remember when your stereo hissed when you
    turned it up a bit?
    Bob, Oct 10, 2004
  7. ISO is a measure of the film or sensor speed. Old measure was ASA.
    Digital cameras can adjust the sensitivity usually from 100 to 400
    ISO, with 400 being the higher sensitivity. Higher sensitivity
    introduces more noise (artifacts in the picture) so in automatic
    systems the camera set to the lower sensitivity if there is enough
    Yes, the only problem with slow shutter speeds is that the subject may
    move or the photographer may move the camera and cause blur.
    -2 to +2 refers to stops from the indicated setting or as some cameras
    indicate it is a change of sensitivity of the sensor. Basically it
    means giving more exposure or less exposure than what the camera
    automatically selected. E.g. the camera selects f5.6 and 1/125
    second, if you want more exposure then select +1 which will either
    open the camera to f4 or slow the speed to 1/60 or it will change the
    sensitivity from IS0 100 to ISO 200. +2 is double that of +1 or 4
    times 0 setting and -1 is 1/2 of 0 and -2 is 1/4 of 0.
    George E. Cawthon, Oct 10, 2004
  8. Martin Lynch

    mcgyverjones Guest

    No. ASA is American Standard, ISO is International Standards -- a
    combination of ASA and DIN (German Standard)
    So, ASA 400 is DIN 27*, combined they are ISO 400/27* (with a degree symbol
    not "*" after 27)

    mcgyverjones, Oct 11, 2004
  9. You would do well to get a beginning book on photography. It will explain
    these matters better than what you are likely to get in a newsgroup. It
    doesn't matter if the book is about film or digital photography. The
    answers for all these basic questions do not depend on the medium that
    senses the light.

    Even better, look for an adult education course at you local school or
    Marvin Margoshes, Oct 11, 2004
  10. uhh. Yeah didn't I say that. In the U.S. we don't usually care about
    DIN ratings unless you have a German camera or use German film and
    then we still don't care. ISO is just a newer rating sytem and ASA
    100 and ISO 100 are the same. So what whas your point, are you
    George E. Cawthon, Oct 11, 2004
  11. Martin Lynch

    Ron Baird Guest

    Greetings Martin,

    There are some good pages on the web that will reveal this and help you
    understand the reference.

    ISO (International Standards Organization) relates to an agreed upon
    standard across the industry and world to standards used in the many
    processes used in the creation of products. For film or digital, and how
    ISO effects you, think of how a given film or CCD reacts to light. For
    example, the sunny sixteen rule (an old way of setting your manual camera
    for correct exposure) states that if you set the shutter to the ISO and the
    aperture of your lens to F/16 you will get a good exposure on a sunny day.
    So, if you used Kodak Gold 100 film or set your digital camera to 100, you
    would set the shutter to 100 or - if you have an old camera - the closest
    setting of say 125 (a digital camera would do this for you). Then set the
    aperture to F/16. This would give you a correct exposure on a sunny day.

    The F/Stop in a camera is how light is measured. changing one F/Stop either
    doubles or halves the exposure of amount of light that is reaching the
    film/CCD. Hence going from an F/Stop of F/16 to F/8 increases your exposure
    by a factor of two times (doubles). In the reverse, a change from F/8 to
    F/16 it halves the amount of light. This also works for the shutter in the
    camera. Going from a shutter setting of 1/125th second to 1/250th second
    halves the amount of light reaching the film/CCD while going to other
    direction it doubles it (1/250th to 1/125th). The slower the shutter the
    more light is allowed to reach the film/CCD.

    The ISO then relates to how sensitive the film/CCD may be. So, if it is set
    to 100 and you go to 200 then the film/CCD will be twice as sensitive.
    Knowing this you can control the shutter and aperture of the camera to give
    you the exposure you want. The three together allow you a great amount of
    control over the light reaching the film/CCD. With digital cameras, this is
    done with a computer and sophisticated mechanisms, i.e. electromechanical
    aperture shutter combinations. For single lens reflex cameras you often
    have manual as well as computer controls and specific shutter and aperture

    The greater the sensitivity of film or CCD, the higher the ISO will be. So,
    a 400 speed film is more sensitive. Try the following sites for reviews and

    There are more, and there is publication offered by Kodak that you will have
    to call about. But if you search the web you will find much more on this

    Talk to you soon,

    Ron Baird
    Eastman Kodak Company
    Ron Baird, Oct 22, 2004
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