Concurrent flashing or the "secret" to real speed increase when push developing

Discussion in 'Exposure Discussion' started by Helge, Aug 20, 2018.

  1. Helge

    Helge Member
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    I know there has been threads on this topic before, but here is a fresh stab at it, with a recap of some the most interesting of the old threads and articles.

    There is a common idea that it's impossible to get a real speed increase of film over rated speed.
    Pushing is just skewing the top of the sensitivity curve, with little impact in the bottom end. Effectively increasing contrast by accentuating the well exposed parts of the film, and leaving the less well exposed parts less affected by more development.

    AFAIK this is a result of films photochemical flavor of hysteresis and part of what is called reciprocity failure.
    RF seems by some people only to be associated with long exposures, but is in fact close to the core of the problem of film speed as such.
    The quantum efficiency of much film is low in part (mostly) because:
    A certain threshold of activating photons need to be overcome before the grain is developable.
    And, grain that is just on the threshold will "fall back" or regress if left, for sometimes even a short moment without additional photons.
    So it is these two combined and connected factors that creates what could be described as the inertia of film.
    That is, at least as far as I understand.

    The most commonly accessible, non development oriented way of getting a real speed boost in motion picture film, is pre or post flashing (often combined with pushing).
    Flashing of paper in still photography is well known but less commonly used with film in still photography (though plate people seem to know and use it).
    This is probably caused by the (perceived) inconvenience, fear of not doing it right (no fast and hard rules or math) and the requirement of the material having to be used shortly after the process, when preflashing.
    Then.
    How about doing it at the same time as exposure?

    In the seventies cinematographer Gerry Turpin came up with a simple devices that would flash the film at exposure. Taking many of the concerns and compromises out of the equation.

    https://theasc.com/magazine/mar98/glory/pg3.htm

    "The Lightflex consists primarily of an oversized filter-hood faced with optical glass. Dimmer-controlled quartz lamps built into the hood reflect into the lens and overlay a controlled amount of light on the scene to be photographed at the time of exposure. The device can be used to adjust the gamma curve of the emulsion, and also extends its photometric range without affecting grain. Francis would come to regularly use the Lightflex, which became an integral part of his photographic process. This acessory was later developed into the Arriflex VariCon. "I found the Lightflex to be an absolutely fantastic tool," the cameraman says. "After Arriflex bought and improved the design, Volker Bahnemann of Arri New York sent me one of my own. I don’t think many people use them, except for students. They’re always ringing and asking me if they can borrow mine!"
    At first it was used mostly for effect and for controlling contrast, but soon Gerry realized that it was actually good for gaining a number of real stops of speed and for getting more shadow detail in high contrast scenes.
    In other words, dynamic range can be traded for speed.
    A bit like how DR goes down with digital at higher ISOs.

    You could view this as an analogy to dolby noise reduction on tape, or perhaps even more apt bias current for magnetic tape heads, only for images.
    You add bias while recording and remove it in post.

    Gerry Turpin did a number of iterations of his original Colourflex, won an academy award in 84 and sold the rights to Arri who made the Varicon. Panavision soon followed with a clone of their own.
    The major difference though, is that both of these (Arri and Panavision flashers) are based on Tiffen light diffusion filters, to be able to make them flat (into a slot on a matte box) instead of the right angle reflector of Turpins original.
    This sacrifices sharpness and makes them more of one trick effects devices, rather than the more general possible applicability of the original Flex.

    Now the basic idea of concurrent flashing has been done and used in two instances for still photography that I am aware of.
    Once in an enlarger, for contrast control, in much the same setup as Turpins flasher, and more importantly in this device:

    https://books.google.dk/books?id=LAEAAAAAMBAJ&pg=PA49&lpg=PA49&dq=concurrent+photon+amplification&source=bl&ots=_oYlSIc7DK&sig=c0KbkVXYi79IwU2bsw3mUXWbtYY&hl=en&sa=X&ved=2ahUKEwjBwYG2vfvcAhUR_qQKHUHiAgAQ6AEwAnoECAgQAQ#v=onepage&q=concurrent photon amplification&f=false

    http://www.dtic.mil/dtic/tr/fulltext/u2/a151831.pdf

    https://books.google.dk/books?id=qUZnDwAAQBAJ&pg=PR72&lpg=PR72&dq=concurrent+photon+amplification+film&source=bl&ots=PzYuozch3y&sig=bc6s-NH5jnPEop78vPrJQP1IZls&hl=en&sa=X&ved=2ahUKEwi-roz4vvvcAhWByKQKHQcnDHUQ6AEwAnoECAgQAQ#v=onepage&q=concurrent photon amplification film&f=false

    I don't know if the Concurrent Photo Amplification (quite a bad name BTW) was developed in response to Gerry Turpins Flex, but it works in fundamentally exactly the same way, only inside the camera.

    This technique seems to really have worked and be very simple to implement, in or outside the camera,
    Why hasn't it been used more, or been built into cameras as a standard feature or sold as a separate powered filter?

    Could this be combined with various other kinds of hypering (flashing is often described as a type of simple hypering). I.E gas hypering?
    Forming gas, ammonia and mercury (bad for health, of course) hypering has been shown to be good for general applicability for speedups outside of long astronomical exposures.
    Combining pushing, concurrent flashing and gas hypering of some kind could potentially get us at, or close to the quantum efficency of electronic sensors?

     
    Last edited: Aug 20, 2018
  2. darkroommike

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    It's all been done, of course. One of the photo magazines even had an article on a camera mod to add light to the film chamber using a "grain of wheat lamp" (pre LED very small incandescent lamp) for a concurrent flash exposure. (Probably Petersen's Photographic sounds right up their wheelhouse). Several slide duplicators also used either pellicle mirrors or fiber optic cables in the bellows to add the concurrent flash also, though here it was more about contrast reduction, by boosting shadows, than for film speed. The advantage of a concurrent flash for film speed boost is that with a switch you can selectively apply it only when needed. Press photographers used to "shoot the sky" to pre-flash plates and film for the same reason. Post flashing or pre flashing in the darkroom can also be done with a very dim bulb behind a Wratten No. 3 safelight filter.

    Hypering also works as does more energetic film developers like Microphen. In the end, no matter which method you you or even if you combined methods you will get about 2/3rds to one stop true boost in film speed; even if you combine methods, end result, is one stop boost.
     
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    Helge

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    Yeah the grain of wheat lamp is the original article from the early seventies, that was in a version in various publications. It involved gutting a Nikon camera or having it done at considerable expense and with a massive battery attached. No wonder it never succeeded.
    It was also mostly only good for black and white, the colour temperature being much too warm for anything else. Something not improved by the the red LED version a few years later.

    About only one stop:
    Is that something you know out of personal experimentation, or are you paraphrasing others?
    While one stop is nothing to be sneezed at if you need it, I have read of better results. Sadly with no images or bad ones (photocopies, raster prints and such).

    Pushing film like Portra and Cinestill 800 three to five stop seems to yield good, or at least interesting results. The main problem being the lack of shadow detail.
    Concurrent flashing would help that.
     
  4. darkroommike

    darkroommike Subscriber

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    The folks that "push" film 3-5 stops and are happy with the results don't look at the negatives or transparencies (or own densitometers).
     
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    Helge

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    Of course Athiril did some very impressive stuff with preflashing and pushing Superia 800 at 12800 some years ago.
    https://www.photrio.com/forum/threads/fujifilm-400h-pushed-to-iso800.109873/#post-1452876
    Check his other posts including the one with Rodinal predevelopment.

    This could be accomplished "in the wild" with a concurrent flasher, without the bother of a suitable reflector, diffusor and lag associated with and distraction of preflashing.
    Of course also making the effect of the flashing as "fresh" as can be.

    It goes without saying that you needn't go that crazy, but the extreme case clearly shows the potential.
     
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    Helge

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