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  1. #41
    smieglitz's Avatar
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    Quote Originally Posted by Ornello Pederzoli II
    Let me try to untangle this for you.

    CI or G-bar or gamma are all measures of negative contrast using certain reference points of exposure, not density. You measure the density at (exposure) point A and at (exposure) point B (the distance betweent the points differentiates the various systems) and derive a ratio. This can be done only with a calibrated test strip. Once you have measured the developed strip, you can then determine the CI or G-bar or gamma. All film of the same type developed in the same way as the test strip will have the same CI or G-bar or gamma. A blank film or a fogged film, it does not matter, because the CI or G-bar or gamma expresses a degree of development and nothing else. If you develop the TMY test strip for, say, 8 minutes in DK-50 1:1, and you measure the CI as 0.56, then all TMY developed for 8 minutes in DK-50 1:1 will be developed for a CI of 0.56 (aside from emulsion changes).

    What you need to do first is to determine what CI is recommended for your process, and then get some test strips to process. You will need the densitometer to measure these. Aside from this, there is no use for the densitometer.

    OP,

    Having never seen or used a control strip, I have a few questions related to what you've said :

    How could a blank film have any CI or G-bar or gamma other than 0 ? Or do you mean something other than unexposed film when you refer to "blank film"? You later say "...then all TMY developed for 8 minutes in DK-50 1:1 will be developed for a CI of 0.56." OK, granted. However, I don't see how an unexposed TMY sample could be developed to a CI of .56 even though it may have been developed for a CI of .56.

    Aren't these control strips exposed to the same value? I'm assuming they are samples of film stock (e.g., TMY) exposed to a calibrated exposure (e.g., exposed to some standard lux value through a calibrated step wedge). Is that what you mean by "calibrated test strip"?

    I take it you refer to different yet equivalent combinations of film developer dilution, time, agitation, and temperature when you cite the "degree of development." IOW, one could achieve the same "degree of development" with the same control strip developed at Time A + Temperature B or Time B and Temperature A, OTBE. Such an equivolence in development would lead to identical CI values.

    Joe

  2. #42

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    Quote Originally Posted by smieglitz
    OP,

    Having never seen or used a control strip, I have a few questions related to what you've said :

    How could a blank film have any CI or G-bar or gamma other than 0 ? Or do you mean something other than unexposed film when you refer to "blank film"? You later say "...then all TMY developed for 8 minutes in DK-50 1:1 will be developed for a CI of 0.56." OK, granted. However, I don't see how an unexposed TMY sample could be developed to a CI of .56 even though it may have been developed for a CI of .56.

    Aren't these control strips exposed to the same value? I'm assuming they are samples of film stock (e.g., TMY) exposed to a calibrated exposure (e.g., exposed to some standard lux value through a calibrated step wedge). Is that what you mean by "calibrated test strip"?

    I take it you refer to different yet equivalent combinations of film developer dilution, time, agitation, and temperature when you cite the "degree of development." IOW, one could achieve the same "degree of development" with the same control strip developed at Time A + Temperature B or Time B and Temperature A, OTBE. Such an equivolence in development would lead to identical CI values.

    Joe

    1) CI refers to a measure of development. The degree of development is measured using reference points of exposure. Once that is measured, all film of the same kind, developed the same way, will be developed to the same CI.

    2) You could not measure a blank film or fogged film's CI, but if it were developed the same way as the reference strip, yes, it is developed to the same CI.

    3) Yes, you get condtrol strips from the mfr.

  3. #43

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    Quote Originally Posted by Ornello Pederzoli II
    1) CI refers to a measure of development. The degree of development is measured using reference points of exposure. Once that is measured, all film of the same kind, developed the same way, will be developed to the same CI.

    2) You could not measure a blank film or fogged film's CI, but if it were developed the same way as the reference strip, yes, it is developed to the same CI.

    3) Yes, you get condtrol strips from the mfr.
    OP,

    Should you plan to continue discussion of this issue please be more precise with your use of language. If you continue to incorrectly state the facts people will have no choice but to conclude that you don't understand the concepts.

    1. CI is not just a measure of development. It is the result of both exposure and development.

    2. No amount of development will result in CI on a piece of blank film. Joe gave you an opportunity to clear this up but your response above is still seriously flawed.

    Sandy King
    Last edited by sanking; 04-06-2005 at 07:04 PM. Click to view previous post history.

  4. #44

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    Quote Originally Posted by sanking
    OP,

    Should you plan to continue discussion of these issue please be more precise with your use of language. If you continue to incorrectly state the facts people will have no choice but to conclude that you don't understand the concepts.

    1. CI is not just a measure of development. It is the result of both exposure and development.

    2. No amount of development will result in CI on a piece of blank film. Joe gave you an opportunity to clear this up but your response above is still seriously flawed.

    Sandy King

    If I place a test strip in a tank along with a blank piece of film, they receive exactly the same development, right? The blank film is developed to the same CI as the test strip, I just can't measure that is it so because there is no exposure on it.

  5. #45

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    Quote Originally Posted by Ornello Pederzoli II
    If I place a test strip in a tank along with a blank piece of film, they receive exactly the same development, right? The blank film is developed to the same CI as the test strip, I just can't measure that is it so because there is no exposure on it.
    Ahh, waffling a little are we? By your very words you now acknowledge that in order for CI to be measured it requires both exposure and development. Which side of your mouth will you speak from next? Or will you continue to keep flatulating in lieu of communicating in a clear and concise manner?

  6. #46
    smieglitz's Avatar
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    Quote Originally Posted by Ornello Pederzoli II
    If I place a test strip in a tank along with a blank piece of film, they receive exactly the same development, right? The blank film is developed to the same CI as the test strip, I just can't measure that is it so because there is no exposure on it.

    OP,

    They do receive the same development.

    As I stated before, the two films would be developed for the same CI, but not to the same CI.

    There is no density difference, nor contrast, in an unexposed but developed film and hence no value for CI in that sample other than zero. Zip. Zilch. Flatline. Nada. Nothing. Naught. Nil. Nix. None.

    The precision in language your (presumed) alter ego seems to insist upon is seriously lacking in this thread.

    Joe

  7. #47

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    Quote Originally Posted by Donald Miller
    Ahh, waffling a little are we? By your very words you now acknowledge that in order for CI to be measured it requires both exposure and development. Which side of your mouth will you speak from next? Or will you continue to keep flatulating in lieu of communicating in a clear and concise manner?

    I thought I was clear enough. CI is a measure (indirect) of development by means of measured contrast, which, once established, can be used as reference. CI can be measured directly only on tests strips. Kodak describes the procedure in their literature. CI is a target value.

  8. #48
    smieglitz's Avatar
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    OP

  9. #49

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    Quote Originally Posted by smieglitz
    LOL....

  10. #50
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    First of all Michael /OP isn't totally wrong on his concept of blank film and CI. He is just being extreme in the example. People shouldn't be so quick to jump on the trash OP wagon. Sandy's reprimand of OP's use of proper technical terms can be applied to himself. SBR is an out of date and inappropriate term. Brightness is a subjective term and has not been used since the 1950s or 60s. The correct term is Luminance Range which is psychophysical. The abbreviation is generally LSLR. You can also us log-H Range when referring to the characteristic curve.

    If anyone is interested in an authoritative discussion of Contrast Index, there is a paper, Niederpruem, C.J., Nelson, C.N., and Yule, J.A.C, Contrast Index, Photographic Science and Engineering, Vol. 10, N. 1, Jan-Feb 1966.

    Davis is also mistaken as to Ilford's average gradient. There isn't an arc. It is a perpendicular line rising from the 1.50 log-H line emanating from 0.10 over film base plus fog. Ilford established this approach in the early 50s. The log-H range of the line comes from the range used in the fractional gradient method. Kodak's CI "floating" toe anchor point is also related to the fractional gradient method.

    The range of the log-H line is designed to reflect the useful log-H range of the curve. It reflects either the average LSLR - flare or in the case of CI, the arc basically reflects the changing effective log-H range as the contrast increases. The 1.50 range of Ilford was accurate with the old non coated lens and the higher flare factors. Today, average flare is lower, so CI is the most accurate approach. The difference is mostly seen with long toed curves. It also becomes more apparent with film developed to higher contrasts.

    It took me a little while to figure out the discrepancy between Adams target 1.25 to 1.35 DR for a grade two paper and ANSIs 0.95 to 1.15 DR until I realized it was all about flare. Think about it.

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