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Thread: Slide sharpness

  1. #81
    Rudeofus's Avatar
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    Dear Henning,

    so what it basically comes down to is we want insanely high resolution for 1:4 or 1:1000 contrast ratios so we get acceptable resolution for 1:1.5 and 1:1.2 contrast ratios. Wouldn't it be more meaningful to measure resolution for 1:1.5 contrast to begin with? This may be the main problem of the term "film resolution", that it strongly depends on subject contrast yet is often named as universal film property ("Tech Pan is 200 lp/mm!").

    PS: Does anyone know a formula how to calculate the resolution for different contrast ratios of the resolution is know for one? Or is this behavior different for every film (type)?
    Trying to be the best of whatever I am, even if what I am is no good.

  2. #82

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    Quote Originally Posted by Rudeofus View Post
    Dear Henning,

    so what it basically comes down to is we want insanely high resolution for 1:4 or 1:1000 contrast ratios so we get acceptable resolution for 1:1.5 and 1:1.2 contrast ratios. Wouldn't it be more meaningful to measure resolution for 1:1.5 contrast to begin with? This may be the main problem of the term "film resolution", that it strongly depends on subject contrast yet is often named as universal film property ("Tech Pan is 200 lp/mm!").
    Well, yes and no. It is a bit more complicated.
    First of all we have chosen 1:4 object contrast at our last big comparison (so far tested almost 90% of all films on the market) because it is a rather moderate / low contrast.
    In almost all scenes you photograph you have details with such a contrast ratio.
    Therefore the results are valid for most cases.
    We were very happy to find an excellent test chart with this lower object contrast, because almost all other available on the market have higher contrast, most in the 1:6 to 1:16 range.
    So far we have not found a quality test chart with an object contrast of 1:1,5. We have some ideas of making one by our own, but that is not trivial. But we will try it in the future.
    Of course we did tests with objects with an object contrast of 1:1,5 or 1:1,3. But then you can only compare two films and say, that one is doing better than the other.
    But it is impossible to quantify the results.

    Quote Originally Posted by Rudeofus View Post
    PS: Does anyone know a formula how to calculate the resolution for different contrast ratios of the resolution is know for one? Or is this behavior different for every film (type)?
    There is no such formula, because
    - the films behave in a different manner, therefore one formula can not work with all films
    - the relationsship between object contrast and resolution is not completely linear: With most films you have a almost linear relationsship from 1:1,3 up to 1:5, 1:6. But then the curve often significantly flattens.

    Or simplyfied: If you double your object contrast from 1:1,5 to 1:3, you will get almost double resolution with most films.
    But if you increase your contrast from 1:16 to 1:1000 (full six stops) you will increase resolution with most films only by 5 - 10%.

    Best regards,
    Henning

  3. #83
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    Quote Originally Posted by Henning Serger View Post
    Well, yes and no. It is a bit more complicated.
    ,,,,,,,,,,,,,
    But it is impossible to quantify the results.
    ,,,,,,,,,

    There is no such formula, because
    - the films behave in a different manner, therefore one formula can not work with all films
    - the relationsship between object contrast and resolution is not completely linear: With most films you have a almost linear relationsship from 1:1,3 up to 1:5, 1:6. But then the curve often significantly flattens.
    And this says a lot!

    In this thread and the one on Ektar resolution / sharpness, much ado is made about this type of comparison when it is really virtually impossible to do due to the differences in contrast and other effects (such as the Kodachrome relief image referred to above).

    You cannot compare positive with negative films for just the reasons above, and you have great difficulty comparing pos with pos and neg with neg across product lines due to sensitometric differences based on dye types and interimage along with the cited Kodachrome effect.

    I myself am wading through "Photografische Informationsaufzeichnung" by Prof. Dr. Hellmut Frieser (Photographic Information Recording), with thanks to Bill Troop who sent me a copy. I may have more to say later on this, but my German is very rusty.

    PE

  4. #84
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    Quote Originally Posted by Henning Serger View Post
    There is no such formula, because
    - the films behave in a different manner, therefore one formula can not work with all films
    - the relationsship between object contrast and resolution is not completely linear: With most films you have a almost linear relationsship from 1:1,3 up to 1:5, 1:6. But then the curve often significantly flattens.

    Or simplyfied: If you double your object contrast from 1:1,5 to 1:3, you will get almost double resolution with most films.
    But if you increase your contrast from 1:16 to 1:1000 (full six stops) you will increase resolution with most films only by 5 - 10%.
    I would expect such behavior for all films: at first you have linear resolution increase because it takes less and less grains to express the contrast, until to some point where single grains (or lack thereof) represent the contrast and further increase in contrast will no longer increase the resolution. I would describe this with the same formula as first order high pass filter responses (in our case resolution over contrast instead of magnitude over frequency). If we could describe film resolution with key parameters max resolution and cut off contrast we should have a much more meaningful description of film resolution.

    Needless to say: my approach neglects any effects from different grain sizes over contrast compensation of the orange mask all the way to neighboring effects, but it would still be interesting how well my approach can model measured results.
    Trying to be the best of whatever I am, even if what I am is no good.

  5. #85

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    Maybe this is clarified in another 50 posts or so, but why doesn't this graph have a label for the x-axis?! Bad form!

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