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  1. #31
    markbarendt's Avatar
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    Quote Originally Posted by Ian Leake View Post
    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.
    The more I think about this the more I fall bak to this idea.

    The advantage I see is that a classic reading can tell me essentially where to set the camera to get a normally exposed face on the side facing the camera.

    I can then decide how to adjust that reading.

    The idea of following the nose was to "tie" the dome angle to the face angle so that the meter reads the average of the light the subject is getting from the direction they are looking.

    The face is given precedence and everything else is ignored.

    That thought still deserves some experimentation.
    Mark Barendt, Beaverton, OR

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

  2. #32
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    Quote Originally Posted by Steve Smith View Post
    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.
    Western never made a flat incidental light receptor Steve, if you read this link it explains invercones better than I can http://www.johndesq.com/pinhole/invercones.htm, as you will see the invercones for the V and Euro master were bigger than the meters body and were the best incidental light metering receptor ever devised, they had a back leak facility that took into account some of the backlighting and have never been bettered.
    Last edited by benjiboy; 05-15-2011 at 03:35 AM. Click to view previous post history.
    Ben

  3. #33
    Steve Smith's Avatar
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    Quote Originally Posted by benjiboy View Post
    Western never made a flat incidental light receptor Steve.
    I know. It's just in the book they suggest that the earlier invercones are treated in the same way as a flat receptor and the duplex method is used but say that the later invercones already compensate and that one reading pointing at the camera is sufficient.


    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.

  4. #34
    benjiboy's Avatar
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    Quote Originally Posted by Steve Smith View Post
    I know. It's just in the book they suggest that the earlier invercones are treated in the same way as a flat receptor and the duplex method is used but say that the later invercones already compensate and that one reading pointing at the camera is sufficient.


    Steve.
    As you write Steve with the last versions of the invercone the The Duplex Method isn't necessary, but receptor domes on all other light meters that the majority of people use with the conventional dome including even the current top of the line Sekonic, Kenko and Gossen digital meters don't have this back leaking ability in which case Duplexing is appropriate I.M.O. in backlighting.
    Ben

  5. #35
    markbarendt's Avatar
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    I'm still trying to wrap my head around what benefit duplexing or for that matter ever not pointing the dome at the camera might give me.

    Seems to me that both are meant to make a compromise between subject placement and highlight placement and that it normally does that at the "expense" of shadow detail and specific mid-tone placement.

    Also seems to me that that compromise is subjective, surely one based on experience, but still subjective.

    My thought here is that before we choose duplexing, following the nose, or any "split the difference" method, don't we still have to answer the question "where do I want the subject, highlights, shadows to land on the film curve?"

    It seems to me that if I answer that question and take a direct reading, then based on similar experience it would be just as successful and just as subjective to dial in a my own offset, just like I place a zone with a spot meter.

    What am I missing here?
    Mark Barendt, Beaverton, OR

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

  6. #36
    Steve Smith's Avatar
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    Quote Originally Posted by markbarendt View Post
    It seems to me that if I answer that question and take a direct reading, then based on similar experience it would be just as successful and just as subjective to dial in a my own offset, just like I place a zone with a spot meter.
    I don't think you're missing anything here. If you spot meter an area and you know where you want to place the exposure of that area then you have arrived at the exposure settings you want.

    Incident light reading, if done properly, eliminates any errors or adjustments you might normally need to make from 'difficult' subjects (white dresses, black suits, etc.) if using a reflected light reading.


    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. #37
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    I suspect that the 'back leaking' receptors were not adopted by other manufacturers for several reasons. One is probably licensing. Perhaps the most important reason would be the necessity to provide more complex instructions for meter use, because the user would have to learn to stand out of the way of both the incoming backlight and the forward receptor dome/invercone. I can see that being a potential headache given the attention paid to written instructions by many users.

    One thing that is interesting to me in reading Dunn and Wakefield is that they indicate that any reflected light meter can be made into a flat receptor incident meter with a diffuser panel, and that one can construct their own backlight compensating incident dome with half a white table tennis ball if the receptor is small enough. The amount of backlight leakage can be adjusted by increasing/decreasing the amount by which the hemispherical receptor overlaps the meter body. Of course any modifications of a reflectance meter would require some recalibration (an EV or ISO adjustment), but one could calculate that with a few readings compared to a conventional reflected or incident meter. And with a PIC or Arduino, a light sensor, half a table tennis ball, and a little code, one could relatively easily make a back light compensating meter.

    It would be nice if the linked BJP article included the illustrations that are referred to, and the character encoding capable of showing a degree symbol, but it appears he's more worried about theft of his article than disseminating information. (See his page source code.)

    Lee

  8. #38
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    Mark, I see it this way.

    When you use a spot meter, you let's say measure the highlights, read the value, place this 3EV above middle grey, and you know it's going to land, in the film curve, 3EV above middle grey. No matter how contrasted is the scene, you know where that spot lands on the film curve. You also use the spot meter to "scan" the scene and see where other parts of the scene "land" on the film curve. You'll have an idea of where shadows will begin to block. But you will know that your highlights will not burn (supposing you know that in your film 3EV above middle grey give the detail you want).

    Now let's imagine you use an incident meter. An incident meter, whatever you put in front of it (disk, sphere, or any other contraption) gives you an exposure that is:
    - certainly right for a middle grey object;
    - certainly right for any other darker of lighter object, provided that they fall within the capabilities of your film.

    The normal way of thinking is that, when you use incident metering, everything will fall right on film: grey will be grey, dark grey will be dark grey, bright white will be bright white. And that's true, until you reach the shoulder and the toe of your film. In shoulder and in toe you will have less tones, less "description" of the subject. After that, you will have blocked shadows and burned highlights.

    When you take a picture of, let's say, some flour and you want to maintain the flour texture, if you just use your incident meter you place the flour on the upper part of the curve. You might have a very flat rendering of the flour. If you want the "texture" of the flour to be more visible, you close the exposure a bit so that the flour is described by a "more linear" portion of the film curve. The same for the black cat on a coal carpet (you open this time).

    Dome, disc.

    We saw that when using a spot reflected meter, if you know the film curve, you know you will have no surprises on where the highlight fall.
    When using an incident meter on a very contrasted subject (as in the case of extreme lateral lighting of the OP), and pointing the dome toward the camera you are averaging the luminous side and the dark side. Whatever this average is, it is not guaranteed not to burn your highlights or to place them where you will have enough detail.
    If your goal is, as in this case, not to burn the highlights, you don't care how dark shadows will be and you don't want the shadows to skew your calculation. An "average" makes sense only until you know that all your subject is contained in the film curve. If the film curve is not broad enough to contain all your subject, "averaging" might just lead to have both blocked shadows and burned highlights. You place the center of your blanket just over your navel, and you have both your head, and your feet, in the cold.

    In this case, you point the dome toward the light source, so that you know that your exposure will be right in the sense that your highlights will not be burned.

    The rule of thumb is:
    If the subject range is within film dynamic range, point the dome toward the camera. It will nicely average the light values, and you will place your exposure where both highlights and shadows will be correct.

    If the subject range is larger than dynamic range, forget about averaging. Choose what you really want to salvage. If it's highlights you want to preserve, point the dome toward the light source, so that you'll be certain that you will not block the highlights.

    IMO

    Fabrizio
    Fabrizio Ruggeri fine art photography site: http://fabrizio-ruggeri.artistwebsites.com
    Stock images at Imagebroker: http://www.imagebroker.com/#/search/ib_fbr

  9. #39
    markbarendt's Avatar
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    What I'm trying to get at is that turning the incident meters head toward the light source seems to be just as much of a guess as reading the meter normally and closing down a stop to protect the highlights.

    With regard to placement with the incident meter I know that a face will be placed normally if I use a classic reading. If I want what the camera sees to be darker or more dramatic like the example in the OP then I can just close down a stop.
    Mark Barendt, Beaverton, OR

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

  10. #40

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    I would set up a hair stylist's mannequin, or even a basketball or something similar, with two hot lamps on either side. Take pictures at various lighting ratios from 1:1 to as contrasty as you can. For each ratio, make an exposure 1) for the brighter lamp, 2) toward the camera, 3) for the darker lamp (or no lamp) 4) for an averaged reading of the bright and dark sides, and 5) for a duplex reading – and averaged reading of the bright side and the side toward the camera. Let the results inform your decision making in the future.

    You should see that for the exposures numbers 1 - 5 above, respectively speaking: 1) The bright side of the face is well exposed in ratio lighting. In 1:1 lighting, everything is well exposed. 2) The bright side of the face is overexposed in ratio lighting, but if using negative film, there is more on the neg to dodge out of the shadows if you print the bright side down to the "normal" print density. In 1:1 lighting, everything is well exposed. 3) The shadow side is well exposed and the bright side overexposed in ratio lighting. In 1:1 lighting, everything is well exposed. 4) The bright side of the face is overexposed by half the difference between the two readings in ratio lighting. In 1:1 lighting, everything is well exposed. 5) The bright side of the face is overexposed by one-quarter the difference between the two readings. In 1:1 lighting, everything is well exposed.

    You will see that 1) in 1:1 lighting, you can meter with any one of these methods and get good exposures. 2) In ratio lighting, the only way to place the skin in a place on the negative such that it prints to the "right" tone when making a "normal" print (i.e. the only way to get the "correct" exposure for the skin) is to point the dome in the direction of the light. This does not mean, however, that you will have enough shadow detail to suit your taste. In cases in which the lighting ratio is wide, one of the averaging methods (down the middle, average dark/light, and duplex) will compromise the proper exposure for the bright side and the one for the dark side.
    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."

    - Rob Tyner (1944 - 1991)

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