new to digital - ISO

Discussion in 'Digital SLR' started by Harry Weiss, Dec 1, 2004.

  1. Harry Weiss

    Harry Weiss Guest

    I' thinking of getting into digital. I'm not sure of something.
    I looked at some camera specs and saw
    "ISO range (from 100 to 1600 plus ISO 3200 in extended mode)"
    Can I assume that the change in speed in fact changes how the image is
    stored in some way so that the image when taken will require more or less
    light, and when printed/viewed will consequently appear more or less grainy?
     
    Harry Weiss, Dec 1, 2004
    #1
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  2. Yes. To be more precise. Digital ISO correspond to ISO film speed
    so that a digital camera set to a specific ISO setting should be set
    to receive the same exposure (i.e. aperture and shutter speed) as a
    film camera loaded with a film having the same ISO. (YMMV - but my
    experience is that "sunny 16" works pretty much the same with digital
    as it does with film).
    Noisy. Increasing the ISO speed of a digicam increases noise.
    It is a bit like film grain, but IMHO - it looks worse. Take
    a look at the tests at dpreview.com to see how noise at high
    ISO values look like - they usually test dSLRS up to their
    highest possible ISO setting.
     
    Gisle Hannemyr, Dec 1, 2004
    #2
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  3. Harry Weiss

    Alan Browne Guest

    The ISO setting goes to the sensitivity of the sensor. The sensor itself is a
    constant gain sensor, but in between it and the analog-> digital converters is
    a gain section.

    1) It sets the amplification of the signal received on the sensors prior to
    conversion into digital

    2) Its setting is what the metering systems uses along with aperture and shutter
    speed to determine if the exposure is correct. In "auto" modes, the camera will
    evaluate the light and choose the optimal ISO/shutter speed/aperture. In semi
    auto modes such as aperture priority, it will set the shutter speed based on
    your choice of ISO and aperture.

    Digital sensors have constant "grain" regardless of the ISO. But the noise in
    each pixel may be higher as the ISO goes up resulting in 'speckles' due to the
    difference in noise in adjacent sensors.

    Cheers,
    Alan
     
    Alan Browne, Dec 1, 2004
    #3
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