Problem When Using Camera ISO Setting to Compensate Effective Film Speed

Discussion in '35mm Cameras' started by narke, Jan 25, 2005.

  1. narke

    narke Guest


    My camera has an ISO setting scaling 1/3 stop, but the shutter speed
    scaling 1 stop and apperture is 1/2 stop. So, I think there is a
    problem when I want to use the ISO setting to compensate the film

    For a given film, if its effetive speed is 1/2 stop above/below the
    indicated value, what do I do? There is no 1/2 stop for the ISO
    setting. On the other hand, if its effective speed is 1/3(or 2/3) stop
    above/below the indicated value, thought I can set the ISO speed
    exactly matching the speed, but this time since the apperture only goes
    up/down by 1/2 stop, so I believe the result given by the metering will
    not be accurate at all.
    How do you think this? (BTW: the camera is Contax Arial)

    narke, Jan 25, 2005
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  2. The same as you would do with a film camera, only you likely have far
    more control over the film speed. I might suggest, if you have the option,
    to use RAW and make any fine tune adjustments in post exposure.
    Joseph Meehan, Jan 25, 2005
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  3. narke

    Peter Irwin Guest

    On many cameras you can use lens openings between clicks.
    You are trying to be more precise than you need to be.
    The nearest 1/3 stop is never more than 1/6 of a stop away
    from any value. There is no possible way for you to determine
    exposures to better than 1/6 stop.
    It isn't as precise as you wish it to be, but if the actual
    accuracy of the system is enough to support this kind of
    precision you are doing pretty well. I do not know your Contax,
    but many cameras and many exposure meters allow in-between
    settings. Manual shutter speeds are normally fixed in whole
    stops, but in-between settings are normally possible for
    apertures and sometimes possible for film speed dials.

    Peter Irwin, Jan 25, 2005
  4. narke

    Alan Browne Guest

    Don't be afraid of over-exposing negative film by a whole stop, so worrying
    about 1/3 stops is not very important.

    For slide film a slight (1/3) overexpsosure will not harm you in most cases, but
    highlights will burn out for sure. Shoot another frame at 1/2 stop under to be
    Alan Browne, Jan 25, 2005
  5. Your question confuses me, I'm sorry to say. I use slide film, and I often
    intentionally set the film speed incorrectly for certain effects. Having a
    1/3 stop increment works better in some circumstance. If my in-camera meter
    is reading a large piece of the sky for example, and I want the land to be
    correctly exposed, I may change the ISO on the camera by a third of a stop
    so that the land is correctly exposed (or very nearly so) wihthout making
    the sky blue sky appear white in the slide after development.

    I use this trick on my Nikonos camera, which has a meter that reads the
    whole scene and does not allow me to selectively meter an area and lock
    that exposure in. I can't meter land separately, then lock in that exposure
    for the whole scene. With the ISO set 'incorrectly,' I just shoot normally
    with the settings indicated by the camera. The land comes in somewhat
    underexpsoed, and the sky is sky blue as it should be.
    Phil Stripling, Jan 25, 2005
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