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  1. #21
    Steve Smith's Avatar
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    Quote Originally Posted by Lee L View Post
    The duplex method is shown in the book as a correct method with a flat sensor incident meter (or perhaps an invercone), not with a domed meter.
    Yes. I re-read mine recently and realised it was for a flat receptor and that the dome style diffusers automatically carry out the duplex calculation.

    If I get a bit of spare time tomorrow I might do some experiments with my Weston meter with its invercone and a Zeiss Ikophot with it's flat diffuser to see what the variance is as I thought the invercone behaved as a dome rather than a flat receptor as you suggest. I suppose I should go and read that chapter again!.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  2. #22
    markbarendt's Avatar
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    Thanks Lee,

    I just ordered a used book from Amazon, 0.31 + 4.00 for shipping.

    That 130 degree limit and using the flat face actually makes a lot more sense on the duplexing.
    Mark Barendt, Beaverton, OR

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

  3. #23
    Lee L's Avatar
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    Quote Originally Posted by Steve Smith View Post
    If I get a bit of spare time tomorrow I might do some experiments with my Weston meter with its invercone and a Zeiss Ikophot with it's flat diffuser to see what the variance is as I thought the invercone behaved as a dome rather than a flat receptor as you suggest. I suppose I should go and read that chapter again!.

    Steve.
    I haven't read all of the book yet. Discussion of the Invercone appears to be spread throughout the book. My first impression is that they may see the Invercone as having a cardioid response pattern, but that's not based on a complete reading.

    It's a new book to me. I'd heard of it, but haven't seen it locally available or widely discussed in the US. My hardback 1981 copy was ordered through abebooks for US$1 and US$2.99 shipping. It appears to be technically very solid, although a bit dated in areas where some equipment is concerned, but it is based on a 1952 edition with revisions until at least 1981. Well worth a read. They do discuss under what conditions it's necessary to depart from standard metering techniques, and what methods of departure are effective.

    Lee

  4. #24
    Steve Smith's Avatar
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    I have re-read the section on duplex metering but I'm still not sure if they consider an invercone to be equivalent to a flat receptor or a dome.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  5. #25
    Diapositivo's Avatar
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    The original posting shows a particular situation with a very strong lateral light left of photographer and a deep shade on the other side, right of photographer.

    If you point the dome toward the camera, the dome will collect light from both sides and "average" them. If you use the flat receptor and make two measurements and average them, you are going to have more or less the same results. No surprise in that.

    The problem is that, in the specific condition of the picture of the original post, this "averaged" exposure might burn the highlights. When making an incident reading there is no explicit or implicit guarantee that the subject range will fall inside the dynamic range of the film. In a situation like this, where what we are interested in is the face of the subject, which is in the highlights, we want to avoid burning the highlights, and any "average" is a risky choice when using slides.

    The point that was raised is whether, in the specific conditions of the picture of the original posting, wouldn't it be better to point the dome toward the light source, so as to be sure to have a reading which is appropriate for the girl's face, and letting the shadows fall where they may.

    The dome will in any case collect light from its sides, so pointing the dome against the light source is going to give a slightly more open exposure than pointing the disk toward the light source. One can see it as an "average skewed on the highlights" which is IMO the most correct choice for that particular situation.
    Fabrizio Ruggeri fine art photography site: http://fabrizio-ruggeri.artistwebsites.com
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  6. #26
    Steve Smith's Avatar
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    Quote Originally Posted by Steve Smith View Post
    I have re-read the section on duplex metering but I'm still not sure if they consider an invercone to be equivalent to a flat receptor or a dome.
    And now I have read the section specific to invercones and understand it a bit better. The book says that the invercones on the older meters such as the II and III are to be considered the same as a flat receptor and would benefit from the duplex method of averaging between the pointing at the camera and pointing at the light source readings whereas the newer IV and V meters had invercones which compensated for this and only needed the single reading taken whilst pointing at the camera.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  7. #27
    Ian Leake's Avatar
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    It seems to me that there are two ways to skin this particular cat. You can either point the dome at the camera to get a 'proper' reading, then compensate a bit to allow for the bright highlights and let the shadows fall where they may. Or alternatively you can point the dome at the light source (so the meter does the compensation for you), and letting the shadows fall where they may.

  8. #28

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    Pointing the dome at the camera is merely one way of using the tool. You do that if you want to average all of the light sources falling on the subject, on a plane that is parallel with the film plane. My argument is that there are many situations in which that is not the way to get ideal exposures and control; the way I see it, these are most situations (pretty much any situation with shadows). And getting into the habit of following one method for every situation takes away a lot of the control and benefit of using an incident meter in the first place. They are extremely versatile tools. Don't handicap that versatility by blindly following the universally-accepted directions without thinking about why you are doing so, and certainly not without learning exactly how they influence your results. As far as the technical argument for the "meter the light method," I have already explained that ad nauseam.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

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  9. #29
    Ian Leake's Avatar
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    Quote Originally Posted by 2F/2F View Post
    Don't handicap that versatility by blindly following directions without thinking about why you are doing so.
    Wise words

  10. #30
    Lee L's Avatar
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    The reason I point out standard usage and the design parameters of an incident light meter is so that people will have a better understanding of the tool and how it is designed to work. Once that is understood, one understands better what's happening when departing from the method for which the tool is designed (i.e. pointed with incident dome toward camera in the same light as the subject). If a non-standard method of use is portrayed as standard usage, it can prevent that understanding of the tool's design and prove confusing, especially to beginners. Of course everyone is free to use their tools as they see fit. Understanding the design will help with making intelligent departures. See Phil Davis and his incident metering method in Beyond the Zone System for one example, where he shows how and why one can determine subject brightness range with an incident meter in many/most circumstances.

    In practice, under many circumstances there may be less difference between standard readings pointing an incident dome toward the camera and away from it than many people assume, and film latitude (especially negative film) often easily covers many of those departures. The domed incident meter does a great job of integrating a reading in varying lighting circumstances as Dunn and Wakefield (and many others) have mentioned. It's more comprehensive a tool in standard usage than many people give it credit for. The best thing is for people to point their domed incident meters on and off the lens axis under varying lighting conditions and pay attention what happens to the reading.

    The photo linked to by the OP was made with an FA, likely with early matrix metering. If the appearance on screen is indicative of what's on the negative, then I'd say it was underexposed and overdeveloped. The skin goes from blocked up highlights to blocked up shadow in the space of a few inches. To me it looks very much like film that was 'pushed' at least a couple of stops.

    Lee

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