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  1. #31
    CBG
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    Quote Originally Posted by JPD View Post
    ... Green has some yellow in it.
    True if one is adding paint colors but, but here we are talking about adding light and that is rather different. The primaries that matter for film are red, blue, and green. So, with the light impinging upon film, the green light is not the product of adding two other colors.

    For light
    Primaries are red, blue, and green
    Adding primaries gets you the secondaries, cyan, magenta and yellow.
    Red and blue = magenta,
    red and green = yellow,
    green and blue = cyan.
    Red and blue and green (in the right proportions) = white

    In a darkened room if you put the bright spot a strongly gelled red spotlight on a white wall, and then direct the spot from a strongly gelled green spot on top of it, the light you get is yellow. Not intuitive at all.

    But...

    For paint - things are more inutitive:
    Primaries are red, yellow, and blue.
    Adding primaries gets you the secondaries.
    Red and blue = purple,
    red and yellow = orange,
    blue and yellow = green.
    Red and blue and green (in the right proportions) = black

    Weird, huh?

    So, flipping your sentence around - yellow has some green in it.

    So... For film and filters (and I am talking about strong filters):
    Primaries - the blue filters pass only blue,
    red filters pass only red,
    green filters pass only green.
    Secondaries - magenta filters pass red and blue,
    yellow filters pass green and red,
    cyan filters pass green and blue.

    Among other consequences, all that means that to mimic a plain emulsion with a pan film and filters, use a blue filter. To mimic an ortho emulsion, use a cyan filter which passes blue and green.

  2. #32

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    Quote Originally Posted by JPD View Post
    Old german photography books tells about orthochromatic, panchromatic, orthopanchromatic and superpanchromatic emulsions.
    Yea.

    They discovered it and did a lot of the early work.
    Early names later needed to be amened/extended....

  3. #33
    RobertV's Avatar
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    How much red light
    Yes, you can develop by dark red light (used for X-ray development) this TONAL Orthopan film.

  4. #34
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    Rollei Retro 100 TONAL (E.I.80) in AM74/RHS 1+9.
    Last edited by RobertV; 02-01-2011 at 11:34 AM. Click to view previous post history. Reason: resolution example changed

  5. #35
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    CBG;

    When talking about spectral sensitivity, we should forget the concepts of "primary" and "secondary" colors or color mixing. They are relevant when talking about human vision or color products, but when talking about pure sensitivity, the only thing that matters is wavelength - how the emulsion responses to different wavelengths.

    To make this clear, I say "yellow wavelength" instead of just "yellow".

    "Yellow" can be many different things; it can be a mixture of two distinct spikes of red and green wavelengths, or it can be a broad, continuous range of wavelengths from green to red, or it can be a single spike between the red and green wavelengths - this is "yellow wavelength". The point is, the last case (monochromatic yellow) does not record on BW film that is sensitized from blue to green, but the two former record on the very same film; and still, we see all of these yellows EXACTLY the same with our eyes. Color films, or digital cameras, would also render them same, as they are designed to somewhat match human vision by having overlapping spectral responses in emulsions. But, once we are talking about BW emulsion's spectral characteristics, we can forget all that. It's just the wavelength content that counts.

  6. #36
    JPD
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    So green doesn't always contain yellow. A book could be written with all the knowledge from this forum.

    Quote Originally Posted by Photo Engineer View Post
    You also have to remember that the German chemists came up with very "non technical" descriptions for their sensitization which we in the US called by name as short and long red for example, replacing the qualitative names assigned by the Germans. This was probably advertizing, as usually, the US companies didn't mention sensitization except in technical articles.
    Advertizing perhaps, or words invented by writers to simplify things. After all, "ortho-" and "panchromatic" are also words that were invented to fit the sensitizations. Trivial names are often convenient. "Metol" isn't a very good technical description, but is easier to use than... Darn, I can't remember.

    The word "Pan-" was registered to AGFA until 1937.

    Another name for "super-panchromatic" is "ultra-panchromatic":

    http://oi52.tinypic.com/z3m9i.jpg

    (Das Rolleiflex Buch, 1938)
    J. Patric Dahlén

  7. #37
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    Quote Originally Posted by Ray Rogers View Post
    If in addition you also sensitize for red,
    the material can be called "panchromatic"
    (There used to be a few panchromatic b/w papers
    for printing b/w prints from color negs.
    Total darkness was the best safelight.)
    And while the earlier Panalure wasn't very good, by the time I used the later Panalure RC in the late 90s it was quite handy. I wish someone would make such a paper (maybe in FB in a couple of grades) again. I used my Duka 50 sodium safelight set the same as I used for RA4. It was far from bright but did make handling it a lot easier than no safelight, and tested safe for normal times.

    Anyone else miss Panalure? Any chance of pursuading one of the European paper makers to make something like it again?

    /digression.

  8. #38
    Photo Engineer's Avatar
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    To me, Panalure looked a bit like Kodabromide with the curve shape tweaked a tad. It would be possible to make one today provided one could get the right sensitizing dye.

    PE

  9. #39

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    Quote Originally Posted by JPD View Post
    So green doesn't always contain yellow.
    Green never contains yellow.

    The impression of green you get when mixing blue and yellow paints is because green light is not absorbed by those paints.
    It's green, because it does not contain yellow (and blue, etc.) anymore.

  10. #40
    JPD
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    Quote Originally Posted by Q.G. View Post
    Green never contains yellow.

    The impression of green you get when mixing blue and yellow paints is because green light is not absorbed by those paints.
    It's green, because it does not contain yellow (and blue, etc.) anymore.
    So one can say that a yellow-green shade is just that, and is not a mix of anything?
    J. Patric Dahlén

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