Overdeveloping & contrast film vs paper

Discussion in 'B&W: Film, Paper, Chemistry' started by jernejk, Mar 27, 2013.

  1. jernejk

    jernejk Member

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    It's common knowledge that overdeveloping film will increase contrast, right? But why and how does that happen exactly?
    And maybe even more interesting, why doesn't paper show the same effect?

    I never time paper development. But even if I leave the paper soaking for some extra time in developer, I notice nothing like increased contrast. Maybe the whole image gets a tad darker, but that's it.

    Why is film different? What happens when you develop it for 5, 10, 20% extra time?
    Do just midtones turn darker on the negative? I can't imagine shadows (light areas on the negative) become lighter on the negative with longer development, which would really mean the contrast has increased...?
     
  2. Doremus Scudder

    Doremus Scudder Member

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    Film development is, in essence, stopped early in order to achieve the desired density range and contrast. Film is formulated to take advantage of this. If you developed film until it stopped changing density, you would have an unusable negative.

    Increasing development for film increases the density range (up to the max possible, that is) and increases image contrast, moving the mid-tones and the highlights up the curve and making them more dense. Reducing development has the opposite effect. Changes in development time also affect film speed; more development = a bit more speed, less development = a bit less speed. This is a less pronounced effect, but careful workers take film speed changes into account when changing development, especially when reducing development time. I add extra exposure for those cases to compensate for the loss of effective film speed and to preserve shadow detail.

    Read up on the Zone System if you are interested in more.

    Paper, on the other hand, is almost always developed just about as much as possible. In fact, usually extending development of paper simply moves the curve, in effect, increasing the effective paper speed, but does little to the contrast. Papers are formulated to work this way.

    Really, although film and paper both rely on the development of exposed silver halides, they are very much different beasts.

    And, do time your paper development!

    Best,

    Doremus


    www.DoremusScudder.com
     
  3. markbarendt

    markbarendt Subscriber

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    Black and white papers do show the same effect, that's why consistent time and temperature or judgement based on inspection is valuable. Color papers are closer to "develop to completion" and have less wiggle but some does exist.

    Assuming a specific grade of paper developed a certain way, an image is created within a specific range exposure, outside that range you get either black or white even when there is more detail available on the negative. So for example in normal circumstances maybe 2/3's of the info available on the negative will fit in the paper's range.

    The enlarger controls general paper exposure. Typically we pick a specific point to peg that exposure to, like the highlights or the shadow point or a skin tone. For clarity I'll stick with simple one-shot exposures. In this normal usage we only get to pick one peg point.

    The negative controls all the local exposures within that general exposure.

    A film that has had extra development has a steeper curve and crosses the paper's range quicker so will only print say 1/2 the detail from the negative. A film that gets less development as a flatter curve and takes longer to cross the papers range and prints maybe 7/8ths of the detail from the negative.
     
  4. jernejk

    jernejk Member

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    Ahh, so film is capable of much higher Dmax, but at max Dmax the negative is impossible to print even on the lowest grade paper?

    And paper, on the contrary, has relatively low Dmax and we want to achieve it to have pure blacks anyway?

    So proper developed film is developed just enough to get shadow detail (shadows develop the last, right?) and highlights in the usable range?
     
  5. jp498

    jp498 Member

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    I consider the paper to be already high contrast, and dektol is fairly high contrast. developer. You could manipulate paper development more finely with very dilute developer, but there's little practical reason to do so.
     
  6. DREW WILEY

    DREW WILEY Member

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    Film and paper behave in an analogous manner, though film typically has a lot more flexibility for time/contrast development control. Some silver-rich papers do allow a fair amt of tweaking in this respect, though underdevelopment per se is likely to affect image tone. Nowadays variable-contrast
    papers are really more engineered to accommodate the contrast variable via the color of exposing light,
    but some of them still have a degree of contrast flexibility simply due to length of development, a fact
    which I routinely capitalize on. But you still need to be well within the ballpark, so it's best if your
    original negative is reasonably matched in contrast to the parameters of your chosen paper and its developer.
     
  7. ic-racer

    ic-racer Member

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    Film development adjusts highlights, not shadow detail. Film exposure adjusts shadow detail. Your 'usable range' will be determined by many factors including flare on enlarger lens, type of enlarger, type of paper and paper developer etc.
     
  8. Vaughn

    Vaughn Subscriber

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    Shadows develop first, then pretty much stop as all the exposed silver gets developed.

    I 'over-develop' because I use a printing process that can handle just about all the contrast a negative is capable of generating.
     
  9. markbarendt

    markbarendt Subscriber

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    Nope. A negative film's D-max and D-min is IMO the wrong way to think about this, while D-max & min can be measured, they are not truly relevant as those points are normally well outside the range that the paper will print detail from. (Slide film D-max and D-min are very relevant, as is a print's.)

    Negatives are normally a low contrast rate (flatter) medium. Paper a higher contrast rate (steeper) medium.

    Film and paper have a fluid relationship, adjusting the exposure of both and the steepness of both of their curves by film development or changing paper grade, controls the range of detail that "straight" prints.

    As a mental exercise, matching all the variables is more like dancing than lab work for me.
     
  10. DREW WILEY

    DREW WILEY Member

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    I'm glad I learned the tricks when graded paper was the norm, because it made you conceptually aware
    of the film/paper relationship. Today's VC excellent papers do offer quite a bit more flexibility, and not
    just in terms of pretending what hypothetical grade the pertain to at a given color of exposure - they're
    adaptable to all kinds of technique. But I still think it's worthwhile for a beginner to get ahold of what's
    left of graded papers just for the learning experience.
     
  11. Michael R 1974

    Michael R 1974 Subscriber

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    This question borders on tone reproduction, but to keep things simple, perhaps a helpful way to think about it is that the film is used to record information from the original scene. In that sense, you only need to use enough of the film's potential density range to record the desired detail in the original scene. Whereas when it comes to the paper, one is usually trying to use the maximum density range the emulsion/paper has to offer (white to maximum black). Of course this is a great oversimplification and there are no rules, but for the sake of generalization it may (or may not) help to think about it in this way.
     
  12. Gerald C Koch

    Gerald C Koch Member

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    Papers are usually considered to be developed to completion. When developing prints development is continued until there appears to be little change in density or contrast with time. In a print you are trying to obtain good blacks. This is not true of film. So trying to compare film and paper is like comparing apples to oranges.

    Studying a good book on the Zone System will go a long way to explain your questions.
     
    Last edited by a moderator: Mar 27, 2013