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  1. #41
    Bill Burk's Avatar
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    It all seemed so simple back in the day when dad and I made a copystand out of a sheet of plywood, clamped on a couple photofloods, screwed a close-up filter on the Spotmatic II and put a graycard on top of the book to set the exposure before shooting.

  2. #42
    Stephen Benskin's Avatar
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    Quote Originally Posted by Bill Burk View Post
    It all seemed so simple back in the day when dad and I made a copystand out of a sheet of plywood, clamped on a couple photofloods, screwed a close-up filter on the Spotmatic II and put a graycard on top of the book to set the exposure before shooting.
    And a lot of very smart people worked really hard to make it that way. "You push the button..."

    BTW, there's more of that excerpt from Connelly's paper.

    "Equally it should be noted that the geographic mean is a convenient measure for the sensitometric determination of film speed of reversal color films as will be shown later, and as such is of considerable importance. The use of the cadmium sulphide photo-resistive cell has made available much more electrical power than formerly and this, of course, appears as an immediate advantage; but some caution is necessary. If the greater power availability is used to reduce to a small value the area of the scene from which light is received, the measurement made is no longer of the average scene luminance which it has been stated above is that on which the photographic constant P, as defined later, is based. In this case, it would be necessary to know which part of the scene to select to obtain a measurement equal to the average, or alternatively, a measurement of either the maximum or the minimum luminance could be made, but then a different value of the constant P would have to be determined and used."

    That last part is a little unsettling.

    Bill, instead of eventually retyping the whole article, I've decided to upload a pdf version of it. Now you don't have to read it in installments.

  3. #43
    Bill Burk's Avatar
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    Found the omission that made this paragraph hard to grasp...

    Quote Originally Posted by Stephen Benskin View Post
    The large majority of exposure determining devices make a measurement proportional to this arithmetical average and in consequence it is this quantity which is used in exposure determination.
    It may be noted here that it has been stated that the geometric average of the scene luminance is the better measure for the purpose of exposure determination

    Quote Originally Posted by Stephen Benskin View Post
    , but because this quantity is no more closely related to the ratio of the extremes of luminance than is the arithmetic average, and moreover is not easily measured, it is not used in exposure determination for ordinary photography.

  4. #44
    Bill Burk's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    ... the measurement made is no longer of the average scene luminance which it has been stated above is that on which the photographic constant P, as defined later, is based. In this case, it would be necessary to know which part of the scene to select to obtain a measurement equal to the average, or alternatively, a measurement of either the maximum or the minimum luminance could be made, but then a different value of the constant P would have to be determined and used.
    I think this can be loosely translated... "If we make a spotmeter, then photographers will have to know where to point it."... "and if they point it at a shadow or a highlight, they'll have to know where to set the dial"

  5. #45
    Stephen Benskin's Avatar
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    Quote Originally Posted by Bill Burk View Post
    I think this can be loosely translated... "If we make a spotmeter, then photographers will have to know where to point it."... "and if they point it at a shadow or a highlight, they'll have to know where to set the dial"
    It's the different value of the constant P that makes me wonder, but the paper doesn't discuss spot meters any further. BTW, P is a big part of the answer in the thread about the relationship between film speed and the metered exposure point.

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