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  1. #71
    Ian Grant's Avatar
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    Crawley's original definitions.

    In order to discuss present-day films usefully, it is necessary to define four terms - acutance, resolving-power, sharpness, definition. Acutance, as we have just seen. is a scientifically measurable quantity which is directly related to the measurement of density gradients. Now when acutance is high, sharpness will be good; therefore one might say that acutance is the scientific measure of sharpness, which latter is a visual or psycho-visual effect. ' Sharpness' is usually associated with the overall impression of a print or projected image, judged from normal viewing distance for its size; 'definition' on the other hand may have to be judged from a closer viewpoint, and refers to the extent to which fine detail is recognisably rendered. When the acutance with which fine detail is rendered is high, then definition will be pronounced good. Resolving power or resolution refers directly to the ability of a lens, film, or developer, or any combination of these three, to record detail, and like acutance is a scientifically measurable quantity, so long as the conditions and criteria used are stated, Just as acutance is the measure of visual sharpness and efinition, so resolution is the measure of the actual fineness of detail rendered.




    His summary in a later shortened version:


    " Sharpness "-
    the overall impression of a print or projected image, measured scientifically as "acutance ", seen from normal viewing distance.

    " Definition "
    -the extent to which fine detail is recognisably rendered in a print, etc. When acutance of fine detail is good, then definition is good.

    " Acutance "
    -the contrast at the edge of significant detail, a scientific measurement of the density gradient at that point.

    " Resolving Power "
    -the scientific measurement of the actual fineness of detail recordable by a lens, film, or developer, or any combination of these three.

    Ian

  2. #72

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    I have Crawley's articles from which you quote.I suggest that Crawley never stuck to his original definition of acutance as a scientifically measurable quantity.
    For instance in BJP Jan 27 1961 p41 he says of FX-2...."If agitation is reduced to every other minute or third minute with an increase in time up to 1/3 or 1/2, negatives of interesting internal gradation and acutance may be obtained...".
    The acutance he refers to here includes adjacency effects,as Dr Henry explained it is not a scientifically measurable quantity.

  3. #73

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    Quote Originally Posted by Photo Engineer View Post
    ....Then there is the factor that is contributed by edge effects which brings up the topic of macro vs micro contrast. If you design the film to have high micro-contrast, then the contrast of fine objects is higher. This film functions well for 35mm. Actually, most films have graded high micro-contrast, medium contrast wider images and lowest contrast for macro images. Thus the transition from 35mm to 4x5 for example, with one film, may give a different visual result in the same developer, but then again, under good conditions, the images should be identical for detail.

    PE
    This should show up rather strongly in a sine wave MTF test, but I have never seen it.

  4. #74
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    Quote Originally Posted by nworth View Post
    This should show up rather strongly in a sine wave MTF test, but I have never seen it.
    This is a repeat of the micro and macro scans of edge effects and the resultant plots of contrast at each density. You can thus easily demonstrate micro and macro contrast. BTDT.

    PE
    Attached Thumbnails Attached Thumbnails Edge Effects.jpg   Micro Contrast.jpg  

  5. #75

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    And this is in Haist in the same chapter as the Altman/Henn study.

  6. #76
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    Well, this data is from Kriss about 19+ years after the Haist book.

    PE

  7. #77

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    Apologies. I thought this was in the book but going back to check it was a chart specifically on Eberhard effect.

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