Push/Pull basic questions

Discussion in 'B&W: Film, Paper, Chemistry' started by jsimoespedro, Dec 15, 2012.

  1. jsimoespedro

    jsimoespedro Member

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    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
     
  2. Bill Burk

    Bill Burk Subscriber

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    I'd say you are right on both statements.

    When you develop longer, more metallic silver grows... thus more grain.

    Literally ISO never changes, but that's just a nerd's fact. Call it exposure index when it's not "standard"... EI can be set higher on your camera if you develop longer. That's pushing.

    When you develop less time, the difference between the clear and the darkest parts of the negative isn't as great - because of the same reason... the metallic silver hasn't developed as much.

    The difference between dark and light is contrast, so that's why less development is less contrast.
     
  3. jsimoespedro

    jsimoespedro Member

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    Thanks.
     
  4. cliveh

    cliveh Subscriber

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    Why do you need to push/pull? Why can’t you use the correct film, exposure in the first place? Be aware that when you increase development you also increase base fog.
     
  5. kreeger

    kreeger Subscriber

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    It depends... on many factors. If you are talking about box rated film speed then here is some observations.

    Pushing
    If you are using medium format, regardless of Box rated ISO speed, depending on the illumination of the subject matter, when pushing, you will see less shadow detail, which may appear as high contrast.

    Grain
    If you are using medium format, slower ISO 100 and below film, you will not likely see a grain difference except under enlargement over 8x10 when pushing.
     
  6. MattKing

    MattKing Subscriber

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    For clarity, "pushing" and "pulling" refer only to modifications of your development time. The reason that one decides to modify the development time is that one wants to modify the contrast of the film.

    A "push" development increases the contrast. It also tends to push the area of the curve near the toe up into the straight part of the curve. By doing this, we make flat subjects appear more contrasty. We also improve slightly the appearance of the shadows and near shadows in films that have been underexposed. A "push" development is often used when we are forced to underexpose film (i.e. meter using a higher than box speed EI). For negative film, a "push" development gives little or no improvement to the underexposed shadows. It may help though with shadows on transparency film.

    A "pull" development decreases the contrast. It also tends to push the area of the curve near the shoulder down into the straight part of the curve. By doing this, we make contrasty subjects appear less contrasty. We also improve slightly the appearance of the highlights and near highlights in films that have been overexposed. A "pull" development is often used when we are forced to overexpose film (i.e. meter using a lower than box speed EI). Most negative film has a lot of latitude for over-exposure, but even so a "pull" development may make it easier to print over-exposed highlights. For transparency film, a "pull" development may be very helpful with overexposed highlights.

    C41 negative films tend to decrease graininess when you overexpose them. Other films tend to increase their graininess when you depart from the recommended development.
     
  7. cliveh

    cliveh Subscriber

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    + density and base fog.
     
  8. jsimoespedro

    jsimoespedro Member

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    But what happens if:

    1) Expose at 100, develop at 200.
    2) Expose at 100, develop at 50.

    vs.

    3) box speed 100, expose at 200, develop at 200.
    4) box speed 100, expose at 50, develop at 50

    Makes sense?
    As far as I now, when you over-expose or under-expose, you also correct the development time.

    This is relevant because some manufacturers plot different density curves, keeping E.I. constant, according to development time. The difference you get is a steeper curve as development time increases. For instance check this link, but there are many others available online.
    http://www.maco-photo.de/files/images/Retro80S_aviphot_pan80_en.pdf

    For instance, check the curve "Gevatone 66, G 74 c, 30 °C."
    It seems you can get about 1 stops of extra speed (log exp from -1.8 to -2.4) when you increase development time from 20 to 70 seconds. This comes at the expense of increased contrast - the gradient of the curve gives you the Gama contrast. In this developer and temp combo, it goes roughly from 0.75 to 1.9 at the shadows to mid-tones for the longer development times.

    This tells me it is not the same to "+1 push" to 200 and develop at 200 or expose at 100 and develop as 200.

    As far as I can recall, and I might need to check again, Ansel Adams N+1 meant expose at N and develop as N+1. Right?

    There should be as many options as in the table below. Anyone care to comment?

    [TABLE="width: 500"]

    Expose/Develop

    N-1

    N

    N+1


    N-1

    Published

    ?

    ?


    N

    Adams contraction

    Ok

    Adams expansion


    N+1

    ?

    ?

    Published

    [/TABLE]
     
  9. cliveh

    cliveh Subscriber

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    Can you please return to the real world of observation and reality?
     
  10. Bill Burk

    Bill Burk Subscriber

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    1) Your negative will be relatively "contrasty" - This is like (but not exactly) N+1
    2) Your negative will be relatively "flat" - This is like (but not exactly) N-1
    3) This is the definition of "push one stop"
    4) This is the definition of "pull one stop"

    Push/Pull and N+, N, N- development are different vocabulary used to describe exactly the same thing... But importantly to achieve different goals.

    I am oversimplifying to make a dramatization, don't anyone who shoots in the dark take this as a character attack. When you have to shoot in the dark you have to push...

    Most people "push" film to get a faster shutter speed in a dark bar, in careless or sloppy shooting conditions under pressure where you can't control light. The idea is to get a negative that you can use from an otherwise hopeless situation.

    The Zone System is used to give a negative of a carefully measured and exposed scene, just the right amount of development so that it gives the best quality negative.
     
  11. MattKing

    MattKing Subscriber

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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.
     
  12. cliveh

    cliveh Subscriber

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    When you over develop film you increase density in shadows, midtones and highlights.
     
  13. Bill Burk

    Bill Burk Subscriber

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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...

    [TABLE="width: 500"]

    Expose/Develop

    N-1

    N

    N+1


    Half Rated Speed

    Adams Contraction

    Normal

    Adams Expansion


    Rated Speed

    ?

    ?

    ?


    Double Rated Speed

    ?

    ?

    ?

    [/TABLE]

    [TABLE="width: 500"]

    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

    [/TABLE]
     
  14. markbarendt

    markbarendt Subscriber

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    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.
     
  15. markbarendt

    markbarendt Subscriber

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    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.
     
  16. ic-racer

    ic-racer Member

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    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 a moderator: Dec 15, 2012
  17. Gerald C Koch

    Gerald C Koch Member

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    Concerning pushing; no amount of extra development can create shadow detail where none exists.
     
  18. Bruce Osgood

    Bruce Osgood Membership Council Council

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