Pre-flashing colour film

Discussion in 'Color: Film, Paper, and Chemistry' started by Athiril, Jan 7, 2014.

  1. Athiril

    Athiril Subscriber

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    One of the first films I tried with this was Superia 800 XTRA shot at 12800, with a C-41 process time of 6 minutes.

    EI 12800 no pre-flash
    [​IMG]

    EI 12800 + Zone III pre-flash (Zone III for 12800 that is) - lesser pre-flash amounts did nothing.
    [​IMG]


    I had been planning to apply this to Agfa CT Precisa as well (the made by Fuji stuff), I found N+4 development gave horribly bad dMax on a blank strip of film with no exposure though, so I abandoned that and went normal processing.

    The results with Precisa in normal processing is much more mild of a difference, but it is there. I deliberately underexposed the shots to make sure there were some very low values to have something the pre-flash could affect.


    Underexposure + Zone 0 pre-flash (for EI 100) <-- found no real difference without a pre-flash
    [​IMG]


    Underexposure + Zone I pre-flash (for EI 100) <-- found a noticeable small difference, texture on black clothes, detail on black bags, etc.

    [​IMG]



    I suspect a heavy push significantly helps pre-flash, and will improve contrast and detail in that area of the pre-flash, as with the neg results. In order to do that, I would need to use either a custom first developer with less solvent, or a pre-developer using a normal B&W developer before standard E-6 process. Given I have access to an E-6 processor, that is the easier simpler way for me to try it out to see how much I can squeeze out of Precisa.


    easier to see difference:
    [​IMG]

    [​IMG]
     
    Last edited by a moderator: Jan 7, 2014
  2. DREW WILEY

    DREW WILEY Member

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    You can also differentially correct shadow color bias relative to overall color balance by using CC or light balancing filters for just the preflash.
    I've never been particularly fond of preflahsing, but it is useful to know about.
     
  3. pennyf

    pennyf Member

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    would this work if you post flashed?
     
  4. Dr Croubie

    Dr Croubie Member

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    I'm also curious to know, how exactly did you pre-flash? In the camera, with double-exposure or something? And what was the light source, an actual speedlite flash or something?
    Or was the whole film unspooled, pre-flashed with an enlarger or such, then re-wound?

    I'd be interested to try this with something like Velvia (obviously with a lot of experimentation), get some details in them thar shadows, even at stock EI50 with no pushing.
     
  5. Rudeofus

    Rudeofus Subscriber

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    If you read Tadaaki Tani's book, there is a good explanation why this works. As silver halide crystals receive exposure, they will produce silver atoms on their surface. One silver atom alone is unstable and will go away after short time. Two silver atoms in a cluster are stable, but not developable, Tani calls them latent subimage centers. Only with three (sulfur gold sensitized) or four (sulfur sensitized) silver atoms in a cluster will the grain become developable. If your Zone I preflash creates many latent subimage centers, a much lower final exposure will create developable grains and as a result image detail.

    One thing, though: PE has mentioned a few times here, that the most modern films use two electron sensitation, which I interpret as "a cluster of two silver atoms renders the grain developable", which means such films won't benefit from a preflash. Note, that Athiril uses films that may not have two electron sensitation, as they are a bit older than e.g. new Portra 400.

    @pennyf: very low exposures will form only one silver atom on the grain, and this is not only not developable, it is also unstable and will go away in a very short time frame. It is unlikely that you will see a benefit from a post flash, but YMMV.
     
  6. analoguey

    analoguey Member

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    How did you determine the zone for pre-flashing? I thought pre-flashing was only for paper -interesting to see film use of it.
    (Still unsure of how you can actually do it though)

    Sent from Tap-a-talk
     
  7. DREW WILEY

    DREW WILEY Member

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    I've never cared much for the effect of pre-flashing anything, but did learn to do it correctly, and will admit it's a nice analog method for color
    correcting shadows only. In the field the best way is to have a translucent sheet of white diffusion mylar that fits in a gel filter holder. Mount
    this on your lens (out of focus), with an optional color correction filter. Then expose a blank white sheet of matboard, assuming your camera
    has double-exposure capability. It takes a practice round to determine the exact amt of exposure needed. But it will be a number of stops
    less than your primary exposure, depending on the specific film you use, and the combined density of the items in your filter holder.