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  1. #11
    Lee L's Avatar
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    As Brian Shaw mentions, the Dunn and Wakefield book is an excellent guide. Here is an excerpt on incident metering and the use of flat disc vs hemispherical (Norwood style) diffusers with incident meters. (The Exposure Manual, 4th edition, page 131, column 1)

    As will be seen, the salient feature of these meters is the hemispherical type of translucent receptor employed, whose object is to effect automatically and with a single (camera-direction) reading the necessary correction for most conditions of lighting.

    The claims made for this meter were investigated by practical testing under carefully controlled conditions, and by comparison with the Duplex method using a flat-receptor meter. These comparative tests confirmed that under all lighting conditions except backlighting beyond about 130 degrees from the subject to camera line the exposure indications for a given film speed setting agree within one-third of a stop with those given by the flat-receptor Duplex method.

    The application of the Norwood-type meter is quite simple, and consists of merely pointing the meter's hemispherical receptor directly towards the camera from the subject position, irrespective of the type of lighting employed or its direction up to a lighting angle of about 130 degrees from the subject-to-camera line.
    What's implied here is that the Duplex method is mainly for flat-receptor incident meters, and that domed incident meters compensate in the same way as the flat-receptor Duplex method until the light source is more than about 40 degrees behind the plane of the subject.

    Lee L

  2. #12
    markbarendt's Avatar
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    Quote Originally Posted by Lee L View Post
    As Brian Shaw mentions, the Dunn and Wakefield book is an excellent guide. Here is an excerpt on incident metering and the use of flat disc vs hemispherical (Norwood style) diffusers with incident meters. (The Exposure Manual, 4th edition, page 131, column 1)



    What's implied here is that the Duplex method is mainly for flat-receptor incident meters, and that domed incident meters compensate in the same way as the flat-receptor Duplex method until the light source is more than about 40 degrees behind the plane of the subject.

    Lee L
    I have the third edition of this book, and it is a really great reference.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  3. #13
    Lee L's Avatar
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    I found my copy of Dunn and Wakefield on Abebooks for about US$4, including shipping. It was printed in the UK, and so appears to be more common there. Abebooks.com typically has dealers with copies of the 4th edition (1981) for around $5-$6 including shipping, even shipping from the UK to the US.

    Well worth the money.

    FWIW, I worked in perhaps a dozen professional studios in the 80's, and never saw anyone point an incident meter dome anywhere but at the camera lens from the subject position (or equivalent). Dean Collins advocated pointing at the key light (in artificially lit portraits on low contrast negative portrait films VPS and VPL) and was the first and only pro I knew of advising this. I think his popular portrait training videos were widely viewed and his unorthodox and special-case incident metering advice propagated on the internet and elsewhere by people who didn't have wider training or experience as the correct method for all situations.

    You can, of course, use any light meter in any way that works for you, but the design of the hemispheric receptor incident meter is made to replicate a three dimensional object as seen by the camera, which means pointing the meter at the camera from the subject position (or in the same direction, i.e. parallel to that line, in the same light).

    Lee

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