Incident readings with a digital camera

Discussion in 'Digital Cameras' started by John, Oct 30, 2004.

  1. John

    John Guest

    I have a Nikon 5700. I also use a Minolta IV F incident meter.
    At an ISO setting on both camera and meter, I notice much overexposure if I
    use the Minolta incident reading and the camera on manual setting. Does
    anyone know why, or how to correct.
    Thank you,
     
    John, Oct 30, 2004
    #1
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  2. You may know this already, but the meter in the camera is a relected light
    meter, not an incident light meter. The camera's refected light meter
    measures the light reflecting off the object the camera is pointing at. You
    will get different meter readings if the object is black, white or a neutral
    color. An incident meter only measures the light falling on the object.
    You will get the same incident meter reading whether the object is black,
    white, or a neutral color. Therefore, the two meters can give different
    results.
    If you choose an object that is neutral color, such as a neutral gray test
    card, the results from the two readings should be similar. Remember to
    point the incident meter at the camera. Hope this helps.
     
    Donald Patrylow, Oct 30, 2004
    #2
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  3. John

    Alan Meyer Guest

    How to correct is easy. If the behavior is consistent, you
    can calibrate for the difference by setting the ISO indicator
    on the meter at some fixed multiple of the one on the
    camera.

    You'll have to run some tests, but they should be easy to
    do. Take an incident reading at, say ISO 50. Then shoot
    the scene at various settings on the camera. Also shoot
    it at automatic setting on the camera and check the camera's
    choice in the EXIF data. You'll soon learn how to correlate
    the incident meter readings with the camera behavior to
    get the correct exposure.

    As to why this happens, that's an interesting question.

    It could be that your meter is wrong, but I assume you've
    used it with film cameras and ruled that out. You might
    compare it to other meters owned by friends or at a
    camera store, just to be sure.

    The other explanation is that your camera is reporting
    incorrectly.

    I can see why that might happen. In a film camera, the
    camera manufacturer has to get his ISO settings
    accurately calibrated because he is imaging film. The
    film is not made by him and not matched to the camera.
    He's got to match his camera to the film if he wants a
    proper exposure.

    But in a digital camera there is no independent reference.
    If the photos come out right, the "ISO" sensitivity reported
    by the camera is an irrelevant number that plays no role
    in the camera's internal calculations. Maybe Nikon was
    a little sloppy in computing the number. (I admit though,
    "sloppy" is an odd thing to say about Nikon.)

    Maybe Nikon is just being very conservative. Maybe they
    claim ISO sensitivities of 50-400 when in fact they've got
    100-800, or even 200-1600, because they know that
    people want high ISO ratings and the Nikon engineers,
    no doubt against the wishes of the salesmen, wanted to
    be sure that people got at least as much or even more
    sensitivity than they think they got.

    In any case, this "flaw" isn't anything to be worried about.
    It just means you got a better camera than the specs
    said you got.

    One last thought. The dynamic range of CCD sensors
    is typically less than that of film. I have read that film
    can tolerate more overexposure and still give a good
    image. So it may be that your light meter reads lower
    than it should but the error was not so noticeable when
    you were shooting film with it.

    Alan
     
    Alan Meyer, Oct 30, 2004
    #3
  4. John

    Justin Thyme Guest

    This is what I suspect is the case too. With film, especially B&W negative
    film, the old rule was expose for the shadows and develop for the
    highlights. Your spot meter is most likely calibrated with this in mind.
    However, exposing in this manner on digital is a sure guarantee of blowing
    your highlights. With digital you pretty much have to expose for the
    highlights, and hope that the shadows turn up.
     
    Justin Thyme, Oct 31, 2004
    #4
  5. John

    JPS Guest

    In message <gJ6hd.49558$>,
    I brought this up before, with my Canon 10D. Using sunny f16, or my
    Sekonic meter, the images were exposed much darker than the camera would
    expose at with AE.

    Sure, you can take dark pictures with a separate meter, and make them
    brighter in software, but you are getting a lot more noise and
    quantization. If I used my sekonic more, I'd have to enter 1/2 the ISO
    for JPEGs, and even less for RAW shots where I want to use the full
    dynamic range.
    --
     
    JPS, Nov 1, 2004
    #5
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