Film Speeds During Development

Discussion in 'Talk About Developing Film' started by Ian-Barber, Oct 29, 2016.

  1. Ian-Barber

    Ian-Barber Administrator Staff Member

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    I keeps reading snippets from various sources which say that things such as ...
    • This developer increases the speed of the film.
    What exactly do they mean ?
     
  2. Stephen Batey

    Stephen Batey Well-Known Member

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    The speed of a film is officially defined in terms of how much exposure will give a certain amount of density (above the density of the film base itself and the inevitable fog level). Increasing development time will give some increase in density in the less exposed parts, which is effectively the same as a higher film speed.

    Except that increased development will normally give high contrast - so a speed increasing developer needs to have some means of controlling the contrast.

    Film speeds are determined with a standard developer, temperature, time and agitation to give a level playing field. Which also means that your own backyard playing field which may not be as flat as a mill pond (in plainer language, your possibly inaccurate thermometer, timing method (start when you pour in or when you've finished pouring etc.) and agitation will give a different result - and hence film speed.
     
  3. Ian-Barber

    Ian-Barber Administrator Staff Member

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    Thanks Stephen, I'm guessing then that this is where Semi Stand and Stand development can come into play, extending the development time to increase shadow density with less or no agitation to prevent contrast building up in the high values
     
  4. Stephen Batey

    Stephen Batey Well-Known Member

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    That's how it works. The active developer is exhausted sooner in the areas where it has most to do (the highlights) and can keep on going in the shadows where it's not having to do a lot. Active developer will only replenish the highlight areas through diffusion or developer movement (agitiation) so it slows down.

    The same effect covers the extra acutance you get - in areas where the developer has a lot to do, the exhausted developer will diffuse out slowing development on adjacnet areas, and developer from ajacent areas (still active) will diffuse across to slow development. Hence an "outline" between the areas.
     

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