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  1. #11
    MattKing's Avatar
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    You don't get any meaningful extra speed when you develop more.

    You get extra contrast, which may make your results more usable.

    Remember, the film's "speed" is essentially a measure of the film's ability to render detail in the shadows, and is mostly independent of the film's highlight behaviour.

    Expansion and contraction are used to adjust the contrast (gamma) and the resultant rendering of highlights but, in the most part, they don't affect whether or not shadow detail is captured.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  2. #12
    cliveh's Avatar
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    When you over develop film you increase density in shadows, midtones and highlights.

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  3. #13
    Bill Burk's Avatar
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    I see where you are going with the graphs. By quirky nature of Zone System film speed rating, you commonly use half rated speed. To illustrate the different natures of the purpose of pull/push, I made two graphs to show what goes on...

    Expose/Develop N-1 N N+1
    Half Rated Speed Adams Contraction Normal Adams Expansion
    Rated Speed ? ? ?
    Double Rated Speed ? ? ?

    Expose/Develop Pull One Stop Standard Push One Stop
    Half Rated Speed Pull One Stop Overexposed ?
    Rated Speed ? Standard ?
    Double Rated Speed ? Underexposed Push One Stop

  4. #14
    markbarendt's Avatar
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    Quote Originally Posted by cliveh View Post
    When you over develop film you increase density in shadows, midtones and highlights.
    True but they don't come up equally... density in the shadows (where film speed is measured) only increases a tiny bit, density in the mid-tones increases more, and density in the highlights increases even more.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  5. #15
    markbarendt's Avatar
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    Quote Originally Posted by jsimoespedro View Post
    As far as I now, when you over-expose or under-expose, you also correct the development time.
    While, yes that is suggested in many instruction sheets and other sources, it is by no means required. It also doesn't change the ISO film speed.

    Most sources also admit there is a corresponding loss of detail (on film) when exposing at, for example, 200 instead of the box speed of 100.

    The zone system and its variants adjust development to match measured scene contrast to a given paper grade.

    Another option though is simply to develop the film normally and then adjust contrast with the paper grade.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  6. #16
    ic-racer's Avatar
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    Quote Originally Posted by jsimoespedro View Post
    Hi all,

    Here go some basic questions regarding push and pull.
    What happens to grain size and what happens to contrast?

    When pushing (increasing ISO) you get more grain and more contrast, right?
    When pulling (decreasing ISO) you get less grain and less contrast, right?

    why does grain size changes?

    thanks.

    Joao
    You can only increase ISO with a different emulsion formula, frequently with larger grains. Contrast, or gamma, is the same (by definition) among all defined ISOs. (Gamma = 0.615)
    Last edited by ic-racer; 12-15-2012 at 09:17 PM. Click to view previous post history.

  7. #17

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    Concerning pushing; no amount of extra development can create shadow detail where none exists.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  8. #18
    Bruce Osgood's Avatar
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    Way back in '06 there was a very informative thread on Push/Pull.

    www.apug.org/forums/forum37/31895-why-would-one-push-pull-film.html

    Roger Hicks was an active member then and added a lot.

    I hope I added the link correctly

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