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  1. #101
    Stephen Benskin's Avatar
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    The fractional gradient doesn't have a perfect correlation with the print judgment speed either. All sensitometrically defined speeds are substitute methods for determining film speed. The reason why the fractional gradient method was chosen is because it had the closest agreement over the greatest range of conditions with the print judgment speed.

    Click image for larger version. 

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    I double-checked the paper... Delta-X isn't exactly at the 0.3 Gradient, you don't claim that.
    Ever? Can you point to the specific quote?
    Last edited by Stephen Benskin; 03-15-2013 at 09:59 PM. Click to view previous post history.

  2. #102
    Bill Burk's Avatar
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    Nice chart.

    I just pulled the thought from this quote: ΔX will always equal 0.296. This places the approximate fractional gradient speed point about a stop under the ISO speed point (Hm).

  3. #103
    Stephen Benskin's Avatar
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    Quote Originally Posted by Bill Burk View Post
    Nice chart.

    I just pulled the thought from this quote: ΔX will always equal 0.296. This places the approximate fractional gradient speed point about a stop under the ISO speed point (Hm).
    When adhering to the ISO standard's contrast parameters.

  4. #104
    Bill Burk's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    I have found that long toed cuves have a slightly higher CI index when matching the ISO parameters than straighter curves.
    Me too. I've also found that sometimes I meet the ISO parameters but do not get 0.62 CI.

  5. #105
    Bill Burk's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    When adhering to the ISO standard's contrast parameters.
    Right.

    My emphasis was on the word "approximate" - because for a while in this thread I was trying to get my head around a mistaken concept. I was thinking that ΔX was giving us exact 0.3 Gradient.

    It's OK for me that it's approximate.

    Some things are exact. Like the 0.1 density.
    Some figures are rounded. Like ΔX being 0.296.
    Some things are given tolerance. Like 0.8 density +/- 0.05 in the ISO parameters.
    And some things move around quite a bit. Like the endpoints which you choose to measure CI.

  6. #106
    Stephen Benskin's Avatar
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    Quote Originally Posted by Bill Burk View Post
    Some things are given tolerance. Like 0.8 density +/- 0.05 in the ISO parameters.
    I get the point. Just an FYI. The ISO standard no longer has +/- on the ΔD value. Processing has to be at 0.80.

  7. #107
    Bill Burk's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    ... the closest agreement over the greatest range of conditions with the print judgment speed.

    Click image for larger version. 

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    Again, Nice graph.

    So the 0.1 density is the poorest of all and yet is the basis of traditional Zone System tests.

    This is where I come to the conclusion for myself... I base my EI speed on 0.1 density of the curve that meets ISO conditions closest...

    Then I take Stephen's example in the Delta-X Criterion paper as proof of "approximate invariance of speed" (my quotes), to justify not changing my speed regardless of the developing time I choose.

    I do the tests for any particular film/developer combination - to find the closest ISO curve and take its speed. The rest of the curve family gives me Time/CI which I use to fit development time to shooting conditions.

  8. #108
    AndreasT's Avatar
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    I have a question about the four quadrant reproduction curve graphs. If it is desired that the mid tones in the final print are more contrasty than the shadows and lights how do we choose our films and papers?
    What I mean is it a mistake to look for developer and film combinations which are straight. In combination with paper and developers which are rather straight as well.
    This leads me to a thought which I have been having for a long time now concerning curve shape but I may mention this later.

  9. #109

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    Not an easy thing to answer, Andreas. There is theory, and then there is art (ie one's personal aesthetic preferences). My pictures are of predominantly dark/dimly lit exteriors and interiors, often including light sources in the frame. So I personally want as little compression as possible, especially in the shadows and the longest possible scale in the negative.

    It seems most people respond predominantly to midtone contrast, since that is where most of the "important" information is in most photographic scenes and it is also the range within which out-of-key values and/or local contrast will seem most disturbing or illogical to the average viewer. Does this fit your aesthetic or not?

    Another thing to think about, if you want more contrasty midtones than shadows/highlights, the paper curve does this for you. So if you have shadow and highlight compression in the negative as well, you have a double-hit in the print. Take highlights for example. If they are compressed on the shoulder of the negative, they will likely also fall on the toe of the paper during printing. So they are compressed in the negative and compressed again in printing.

  10. #110
    AndreasT's Avatar
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    Actually I want contrasty shadows and often slightly soft highlights. I do this is my processing since I do flash more than most I expect. Not to save a print but to give me softer warmer lights and colder harde shadows.
    I have just always been looking for films which have straight line. As well as fitting it to my paper a bit. Somehow think that is right. Althought I think it is wrong.
    What I have also thinking about. If we take a straight line from A-B the distance is short, however if we take a curved line from A-B the distance is longer. Translating this to photography the curved line would give us more grey tones. Making it warmer to the emotion.
    Is this the magic of old films.

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