Additive colour printing, understanding lamphouse?

Discussion in 'Color: Film, Paper, and Chemistry' started by Ted Baker, Nov 5, 2018.

  1. georgegrosu

    georgegrosu Member
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    I'm talking about the substractive / additive system used at home.
    Here everyone can improvise something to get better results.
    The main problem is the filters, which depending on the type of filter, some light is transmitted and some of the light is retained.
    Another problem is the mirror, not to mention the dichroic.
    Mirrors are as important as filters because they can change the color of the projected light.
    If you look from a projection mirror in strong light (through the not glossy side), you will see a warm color (reddish) or some cool (blue).
    To have two cine projectors with a very similar light the mirrors are chosen by the above method.
    Note - if the mirror seen in strong light (from the back) has a warm (reddish) color when it is placed in the projector it will give a cool (bluish) light.
    AgX - "Basically additive and subtractive filtering are equal in effeciency, but your experience showed that there may be exceptions with
    the spectral characteristics of the filters in use."
    Yes, additive filtration and subtraction filtration give very similar results for the recommended films, developed normal, fresh, .....
    When the film is different from the above categories, using a filter or a mirror with other features can improve or break everything.
    AgX - "Technically speaking, at least when automatisation is involved, the substractive system has its drawback.
    Whereas in an additive system a mere timer is sufficient, making it much more apt for automatisation."
    From a technical point of view you are right.
    From the financial point of view, the exposure devices on each channel - additive (blue, green, red) - electromagnetic valves are so expensive.
    It costs ~ 3,000 £ just to repair 1 light valves.

    George
     
  2. AgX

    AgX Member

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    The basic way of doing additive filtration is just by controlling the exposure time. Here a timer would be sufficient (as far as exposure times are long enough for neglecting heat-up effects of the incandescant lamp).

    Concerning these light valves your are referring to industrial printers, which regulate the exposures by light intensity.
    I would like to know how Philips with their amaateur enlarger regulated the intensity of their lamps.
     
  3. AgX

    AgX Member

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    In the history of colour photography several tri-colour cameras were made, for still and for cine work. As you said three colour seperations were made simultaneously on three films/plates.

    Used were high-speed panchromatic films. Not neccessarily special films.
    The Kodak Panchromatic Separation Film 2238 you refer to, is a low-speed panchro film intended for copy work.
     
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    Ted Baker

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    One thing that is strange is why the gamma is not specified as 1.0. Instead it appears to be specified as 0.9 - 0.95 for green and red and 0.8 -0.85.

    Putting aside the discrepancy between the red, why is this film developed to exactly 1.0?

    I realise these are very detailed technical questions...
     
  5. georgegrosu

    georgegrosu Member
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    AgX - “The basic way of doing additive filtration is just by controlling the exposure time. Here a timer would be sufficient
    (as far as exposure times are long enough for neglecting heat-up effects of the incandescant lamp).
    Concerning these light valves your are referring to industrial printers, which regulate the exposures by light intensity.
    I would like to know how Philips with their amaateur enlarger regulated the intensity of their lamps.”

    I exposed the color negative on paper with the Janol Color lens (substractive) about 2 - 4 - 5 sec.
    When using the three filters (blue, green and red - aditive) the exposures were different for each filter and were around 10 to 15 seconds.
    At this exposures I have no problems of the transient regime - is not importante for light of bulb.
    At Bell & Howell printer - light valves are functional as diaphragms.
    The valves had the values between 0 and 50.
    These values were given in the program band made for the Color Timing.
    A laboratory printing process whereby the negative is graded for color and density. A color timer uses a color analyzer to look at and adjust the colors of every scene in the movie.
    The analyzer has controls for each of the three primary colors: red, green and blue, and overall density.
    The place where an exposure enters is given by the pinch (the cut of the film on the edge) or by another program band where memories the perforations.

    George
     
  6. ic-racer

    ic-racer Member

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    I can't tell if this thread is about making separations from movie film or still, but for still images, no fancy light source or separation film is needed, just three filters and panchromatic negative film. A non-technical introduction to the process can be elucidated by watching this video of how Elliot Porter's images were made with dye transfer. In this case two different contrast masks were used before making the actual separation negatives.
    Screen Shot 2018-11-07 at 7.39.36 AM.png
     
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    Ted Baker

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    As the OP I can say the research is centred about correctly interpreting the Kodak document referred to the OP which is for motion film. So far it has been my experience that detailed technical documentation in much more readily available for motion picture film. AFAIK still print film works the same (probably identical spectral sensitivities) just the detailed information is not as readily available on the internet, I am sure it is buried in some of the expensive texts on the subject.

    Also the inherent need for multi generation duplication process required in the motion arena, is or was until DIs started to be used very important. The fact that this film still exists highlights this.

    If I could find this stuff for still print film, I would study that instead.
     
    Last edited: Nov 7, 2018
  8. ic-racer

    ic-racer Member

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    https://125px.com/docs/techpubs/kodak/E80.pdf
     
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    Ted Baker

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    Yeah that's the sort of detail. Unfortunately it is for making images from slides or from real-life not for when the source is as negative and the output is another inter-negative/positive etc as generations progress which is what the first document is about.

    I am particularly interested in the negative/positive relationship of traditional negative and print film. In the motion picture arena this is or at least was, something they could do in very repeatable fashion. AFAIK 10 generations could be used with acceptable quality.

    I understand still film is engineered the same, however it rarely needs more than 1 generation.
     
    Last edited: Nov 7, 2018
  10. DREW WILEY

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    I'd be surprised if any Kodak Sep Film is still fully usable. It hasn't been made in a long long time. Dye transfer separations were generally made with Super-XX instead. Nowadays TMax100 is an excellent choice for tricolor separations. A lot of the old specifications relative to both specific film, filters, and developer are now obsolete, though still informative in a general sense. You can still use 29 red, 58 green, and 47B filters under an enlarger lens, but most enlargers are going to have
    a hard time punching through that kind of density, especially the 47B; so a plain 47 is often substituted. Adding a 2B is just for sake of eliminating some UV potentially affecting older enlarger; and you can ignore a 2E too. True narrow-band additive colorheads suitable for this kind of work are not commercially available, though I've built a couple of them for personal use. It's a daunting task. With regular subtractive colorheads, you just set everything to zero and use RGB glass separation filters below the lens. The old Phillips enlarger was basically a toy reliant on common rheostats - absolutely primitive and hopelessly weak compared to modern options. Likewise, the flashtube Minolta RGB colorhead is too weak to be taken seriously for this kind of application. Most professional CMY halogen subtractive colorheads are powerful enough light sources to be used in the manner I just described, with RGB filters below the lens. Under tightly controlled circumstances,
    simultaneous RGB additive printing can yield notably better hue accuracy than ordinary CMY subtractive printing. But one has to have a serious reason and a lot of patience to print RGB in register SEQUENTIALLY, each color at a time.
     
    Last edited: Nov 7, 2018
  11. AgX

    AgX Member

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  12. DREW WILEY

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    That particular product is for making archival interpositives from movie neg film. This thread has gotten a bit confusing with respect to application. I was referring to sheet Separation Film used for making registered black and white internegatives from color chromes, related to dye tranfer printing etc. And true Technicolor was a form of dye transfer printing, in which PRINTS desired from individual frames required intermediate RGB separation on black and white negative pan film.
     
  13. AgX

    AgX Member

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    But the films as such are similar be it 35mm or sheets: panchromatic copy films.
    (Unlees they themselves have to form the matrix for an imbibition process.)
     
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  15. ic-racer

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    From what I can tell the 2238 does not come as sheet film. I'd just do the interpositives. Have you seen the Ctein article?
    http://www.daviddoubley.com/Documents/MakingDyesFromNegatives/E-81NDyePrintsFromNegatives.pdf
     
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    Ted Baker

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    Thanks again, interestingly that same document calls for gamma of 0.8-0.9 instead of what I would imagine should be 1. Could this be as result of the the callier effect. i.e. the gamma as measured by a densitometer is different than the effective gamma when printed with normal light source expected for this use. i.e. diffuse light source?

    If this correct could the wavelength of light be also a variable i.e a shorter wavelength have a greater discrepancy between a densitometer reading and the effective contrast when printed?

    Interesting this document is nearly 20 years old and the motion picture one is current.
     
  17. DREW WILEY

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    AgX - the films aren't similar at all. And Ice-racer, Ted, that old Kodak document was never actually tested in practice! - it was purely hypothetical. I was told that in person by its author. Having recently gone through analogous attempts with modern film, I can confirm that it takes a LOT of fuss and testing to get precise results; and very few people have the kind of precise registration gear and special instruments like I do. But that fact still leaves room for a lot of experimentation potentially
    leading to interesting if not accurate prints.
     
    Last edited: Nov 8, 2018 at 7:53 PM
  18. OP
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    Ted Baker

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    I am using the motion picture document as the definite source for a number of reasons. But I appreciate the documents ice-racer posted.

    Would i be correct in saying that status-m measurements would be taken with a densitometer that has a collimated light source?
     
  19. DREW WILEY

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    Well, yes, a color transmission densitometer reading from a color negative would have to take in account the orange mask. But for actual interpositive and internegative masks and separations on panchromatic film, all you really need is a good black and white transmission densitometer. I am unfamiliar with the motion picture roll product, but assume it's designed with very different gamma and curve characteristics than classic color separation sheet films. Yet it is always useful to read the old related literature too; you can discover at lot of useful tips that way, even though current products and devices have largely changed. But there was a time when skilled workmen held secrets concerning exact methods, which often differed from simplified formal publications.
     
  20. ic-racer

    ic-racer Member

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    Not sure. Here is a quote form OCTOBER, 1934 J. . S. A. VOLUME 24 Densitometry and Photographic Printing. Illumination of the Negative and Its Effect upon Density*, CLIFTON TUTTLE, Kodak Research Laboratories

     
  21. DREW WILEY

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    Quoting a 1934 article on densitometry makes about as much sense as reading about space flight in 1934. Some concepts might remain similar - rockets have been around as long as gunpowder - but the technology has vastly changed. I'm not
    implying old articles are wrong just because they're old; but I wouldn't take things for granted either.
     
  22. Lachlan Young

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    Is this about trying to work out how to remove the mask from colour neg in scanning?
     
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    Ted Baker

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    No that is a fairly trivial issue.

    Perhaps, however I think it still up to date according to this on page 4... :smile: http://www.autex.spb.su/download/wavelet/books/sensor/CH57.PDF

    this goes on to cover the collier effect so perhaps I confer correctly about the gamma in the kodak document referred in the OP.
     
  24. DREW WILEY

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    It gets a lot more complicated. Back then it was nearly impossible to make a sharp color print. I won't go into details. And most color work today involves dye clouds with respect to both chrome and color neg film, which responds or scatters light differently than silver clusters. Then, let's say you next logically bring up the pan film involved in a color separation. Even the classic products available in the heyday of dye imbitition printing had huge harsh grain structure compared to present films, esp T-grain. Yet another issue is how step tablets were made using these same kinds of films. Take a look at an old step tablet and compare it to a new one. All these seemingly minor variables add up. Cumulative gamma itself can be affected, for example by base or emulsion staining sometimes characteristic of old thick emulsion films, even on step tablets themselves. For these reasons, and many many others, there is simply no substitute for doing your own testing with your own equipment, filters, and materials. That being said, I have collected quite a few old Kodak Graphic Art Guides, photo publications, and old sensitometry etc texts. They're highly interesting in their own right. But I've also spoken to a number of old-timers who wrote some of the official Kodak whatevers, and the inside story, as I've already suggested, is sometimes a bit different. It's all fun and informative; but life is short, and one can only master a few specific media.
     
  25. Bill Burk

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    14635695-154B-4B8A-B918-E20E55217039.jpeg Suppose anyone interested in using TMAX 100 to make archival color separation intermediate positives from C41 35mm could make use of this discussion. And then you would use the 2B

    Or anyone who wants to separate a transparency they have on cinema print film (all the slides I had made from 5247 negatives are faded now except one I mounted in glass... and I have the original negs anyway but if that’s what you have...) Then you use the 2E

    But I can answer the nagging question about why not gamma 1... I found a formula... in the 1940 booklet that came with my densitometer... see phot attached
     
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    Ted Baker

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    That's not the correct answer I think Bill, its the correct answer for a different question. The document in the OP is for making duplicates of colour negatives or interpositives where the gamma of the original is correct for the target which is the print film. The gamma needs to have an effective gamma of 1 otherwise contrast will increase or decrease. This should not be allowed to happen otherwise you are no longer making a duplicate. I am guessing there is an allowance for the collier effect.
     
    Last edited: Nov 8, 2018 at 9:43 PM
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