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Thread: Incident light reading

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    Incident light reading

    Just browsing through my Minolta flashmeter VI manual and came across this section which is completely the opposite of what I've always considered was an incident reading.

    The section appears to indicate that an incident reading is from light REFLECTED from the subject as opposed to FALLING on the subject

    Have I mis-interpreted this?

    It's not a typo either as far as I can see

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    Re: Incident light reading

    I think that it is correct, but not written very clearly. The figures are certainly correct.

    If you set your camera exposure based on an incident meter reading, then elements of the scene that have 18% reflectance will be exposed so as to result in an 18% grey (or colour of equivalent luminance). Lighter elements will be brighter and darker elements darker.

    If you set your camera exposure based on a reflected meter reading, let's say a spot meter reading for this example, then the element of the scene that you metered will be exposed so as to result in an 18% grey.

    So if you use incident metering, you get a 'natural' tonal range, but depending upon the latitude of your medium, you may lose highlights, or shadows, or both, and this may be a particular problem if the point of interest of the scene has a reflectance much higher or lower than 18%. Of course you can always take an incident reading and then apply a compensation when setting the camera.

    With reflected metering, you can choose where on the range of luminance levels in the scene you want to put the latitude of your medium, by choosing which part(s) of the scene to meter.

    Hopefully this is not just some more unclear words.

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    Re: Incident light reading

    It's a poorly written piece.

    - An incident light meter measures light falling on the subject and is calibrated to give you the exposure value for an 18% gray reflectance average. The exposure setting will be correct for an 18% reflectance gray subject regardless of the subject's actual reflectance.

    - A reflected light meter is calibrated to measure light being reflected from the subject and provide an exposure setting with the assumption that what it is measuring is 18% reflectance gray on average. If the subject measured is actually NOT 18% gray, the exposure setting will be incorrect.

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    Re: Incident light reading

    Thanks for the input and very well explained.

    My meter has the capability to average out incident and reflective reading with additional settings to ensure highlight or shadow detail is preserved. I guess with the extreme brightness and contrast range over here I'll need to apply all facets.

    This wasn't something I'd previously considered

    The meter is new to me and needs a bit of learning but that initial statement was confusing me.

    Thanks again guys, that's helped a lot

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    Re: Incident light reading

    Quote Originally Posted by ReeRay View Post
    Thanks for the input and very well explained.

    My meter has the capability to average out incident and reflective reading with additional settings to ensure highlight or shadow detail is preserved. I guess with the extreme brightness and contrast range over here I'll need to apply all facets. ...
    You're welcome.

    Remember that a light meter is just that: a device for metering light. If the dynamic range of the subject fits within the dynamic range of the recording medium, then the light meter's reading should provide an accurate guide to proper exposure of that subject.

    However, if the subject's dynamic range is larger than the dynamic range of the recording medium, you .. the photographer ... have to decide based on what the light meter tells you which area of the scene is important and bias the exposure suggested by the meter to capture the scene as best possible.

    The meter's reading is always just a guide to proper exposure!

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    Re: Incident light reading

    Quote Originally Posted by Godfrey View Post
    You're welcome.

    Remember that a light meter is just that: a device for metering light. If the dynamic range of the subject fits within the dynamic range of the recording medium, then the light meter's reading should provide an accurate guide to proper exposure of that subject.

    However, if the subject's dynamic range is larger than the dynamic range of the recording medium, you .. the photographer ... have to decide based on what the light meter tells you which area of the scene is important and bias the exposure suggested by the meter to capture the scene as best possible.

    The meter's reading is always just a guide to proper exposure!
    Thanks Godfrey - it's that bit I keep forgetting!

    Just to conclude - The DR on slide is 5/6 stops?
    And on B+W neg how much?

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    Re: Incident light reading

    Quote Originally Posted by ReeRay View Post
    Thanks Godfrey - it's that bit I keep forgetting!

    Just to conclude - The DR on slide is 5/6 stops?
    And on B+W neg how much?
    In either case, the dynamic range varies both by the film and by the way it is processed, moreso in the case of B&W film.

    My recollection of shooting slide film (mostly Kodachrome 64) was that you had about that range, biased mostly to underexposure.

    For B&W films, development chemistry and process methodology is so great an influence that it's difficult to give an accurate number. Anywhere from 7 to 12 stops is achievable, but the latter takes pretty extreme development processing. Most traditional B&W films are likely in the 7-9 stop range. C41 process B&W films are at the higher end of that scale. Negative films, particularly C41 process, have most of their latitude biased on the overexposure side.

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    Re: Incident light reading

    Thanks Godfrey - you're a star.

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