Pushing C-41

Discussion in 'The Darkroom' started by Marctwo, Oct 15, 2005.

  1. Marctwo

    Marctwo TPF Noob!

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    Does anyone know how to work out the dev time when pushing C41? I've found a bit written about it but there's a lot of conflicting advice:
    • +1 min per stop?
    • +30 sec per stop?
    • +30% per stop?
    Also, I've read that to push E6 you just increase the first dev as you would C41. Is this true?
     
  2. Hertz van Rental

    Hertz van Rental TPF Noob!

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    Pushing colour film is not recommended as it tends to affect contrast and colour saturation - but you can get away with up to a stop.
    For colour reversal film:
    1 stop under exposed = 130% first dev time.
    Correct exposure = 100% first dev time.
    1 stop overexposed = 70% first dev time.
    All other processing times remain the same.
     
  3. photogoddess

    photogoddess TPF Noob!

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    I've pushed both C-41 and E-6 but have done so in the automatic developing machines (Noritsu), not by hand. That entailed turning the machine off for 1 minute during the time the film was in the developing rack. It's possible that's not exactly one stop so I'd just listen to Hertz on this one. He's a smart one. ;)
     
  4. Marctwo

    Marctwo TPF Noob!

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    Thanks for the response, guys.

    I can't argue with that. :thumbup: BTW, how did the films turn out?

    Everything I've read say's not to pull C41 at all but most say push upto 2 stops - which means I'll want to try a film pushed by 3 stops just to see the results first hand. ;)

    Would I simply add 30% for each stop (190%) or compound it (220%) or am I splitting hairs?
     
  5. Hertz van Rental

    Hertz van Rental TPF Noob!

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    The development guide I gave was for E6 processing (clour reversal).
    But for C41 uprating the film by 1 stop (effectively underexposing 1 stop) a 30% increase in first dev time should work as well.
    For uprating more - which I wouldn't recommend - you increase the exposure time by 30% for each stop.
    +1 stop = dev time D + 30% = new dev time D2
    +2 stop = D+30% = D2* then D2 + 30% = D3**
    and so on. I hope that's clear.
    This is only a rough guide and you will need to do a few tests first.

    *compensation for first stop
    **compensation for second stop
     
  6. Marctwo

    Marctwo TPF Noob!

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    Testing is exactly my intention at the moment. ;)

    Cheers Hertz.
     
  7. Marctwo

    Marctwo TPF Noob!

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    Well, I got round to trying this so I thought I'd post an example. I've done standard processing on it as I think it gives a better comparison to a normal finished image than a raw scan. ;)

    The film was ISO 200 shot at ISO 1600 and developed at 220% of normal time.

    [​IMG]
     
  8. Marctwo

    Marctwo TPF Noob!

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    As I sit here scanning another pushed film, it occured to me that maybe this is a bit pointless. :lol: I mean, by pushing the developement I'm just moving the dynamic range to a darker position - I'm not actually enhancing or extending it.

    So I thought why not just develope it normally and adjust the exposure on my scanner to compenstate? I've done so with underexposed shots before with similar results - and it would be far more convenient to underexpose on a frame by frame basis rather than a whole film at a time.

    I'm obviously going to mess about with the idea but I'd be interested in any thoughts you guys may have about it.
     
  9. Hertz van Rental

    Hertz van Rental TPF Noob!

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    By pushing you are under-exposing and then compensating by over-developing. Although this affects grain and contrast it keeps the exposure range in roughly the same position on the curve.
    If you under-expose but process normally then you loose a lot of information in the shadow region - that is, the toe or heel of the curve. This information cannot be recovered by scanning and use of PS because it isn't there to start with. You will also find that the colour and contrast suffer.
    The best course is to buy the fastest speed film possible and if necessary push it. That way you will retain maximum information and quality will not suffer anywhere near as much.
     
  10. Marctwo

    Marctwo TPF Noob!

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    Let's see if I can explain what I mean a bit better.

    Suppose that a film has a dynamic range of say 10 stops (??? just suppose) from 0 (film base/shadow) to 10 (highlights). Most images would use the dynamic range between 2 and 8. Anything above or below starts to infringe on the dynamic limits of the film so it loses detail to the grain or blowouts.

    If you underexpose by 2 stops then your normal image will sit between 0 and 6 but the shadows will now be grainy as they're encroaching on the film base. However, your highlights have been extended by 2 stops which may or may not be useful.

    If you push the developement by 2 stops then the image will be pushed back to the range 2 to 8; But the film base will also be pushed by 2 stops which now makes the dynamic range of the film 2 to 10. The shadows will still be pushing the limit of the film so you'll gain no extra detail but you'll lose the extra 2 stops in the highlights.

    I can scan beyond the dynamic range of the film so I can choose to have my black point at 0 or 2 and my white point at 6 or 8 or 10.

    Now... did you understand a word of that. :lol:

    Is this theory flawed? If so, how so?
     
  11. Hertz van Rental

    Hertz van Rental TPF Noob!

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    Of course.
    Unfortunately the shadow detail normally sits right down on the toe of the curve - at about 0.1 above base fog. If you under-expose, the shadow detail drops below this threshold and is not recorded.
    Pushing the film under-exposes the neg, but extending the development time increases image amplification and moves it back up to a useable position - in effect you are 'fooling' the film into thinking it has a higher ISO.
    The increased dev time increases the size of the silver grains formed in the first development which results in a grainier (noisier) film. The slope of the curve is also affected to reduce shadow contrast and increase highlight contrast.
    Base level fog is increased slightly but as this is in the shadows the effect is minimal. Some extreme shadow detail will be masked a little - but the information is still there and recoverable if you scan it.
     
  12. Marctwo

    Marctwo TPF Noob!

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    Cheers, I'll be trying this out in the next couple of days so I'll post some comparitive results.
     

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