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  1. #1

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    Ilford MG IV RC sensitivity: blue or green?

    So I'm looking at this:

    http://www.interfoto.fi/ilfordphoto/...rit/mgivrc.pdf

    I always hear that b+w paper is "blue-sensitive", but the spectral sensitivity chart here seems to say that while it *is* blue-sensitive, blue is actually in a local trough and that it's *more* sensitive to violet and green, in particular a pronounced hump there at just about the usual range for green LEDs ( ~515nm ).

    Am I just too ignorant to interpret this correctly, or is it true that Ilford MG is more sensitive to violet and green than blue?
    -brian hayden
    http://fed-2.org

  2. #2
    ic-racer's Avatar
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    The blue sensitive emulsion is blue sensitive. The green sensitive emulsion is green sensitive.

  3. #3

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    OK, interesting. I didn't know there were two separate layers. I find the green sensitivity in those charts surprising, because my personal experience with paper negatives and Harman direct positive is that most greens end up almost as featureless as red. Have to ponder why that is, if it's not a feature of the spectral response.
    -brian hayden
    http://fed-2.org

  4. #4
    MattKing's Avatar
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    Brian:

    The variable contrast papers achieve their contrast variation by using two layers - a green sensitive layer and a blue sensitive layer. If the exposing light is low in green and high in blue, contrast will be relatively high. If, however, the exposing light is high in green and low in blue, contrast will be relatively low.

    Most printers effect these changes by using filters with complementary colours - adding yellow ("minus blue") to decrease contrast or adding magenta ("minus green") to increase contrast.

    The green sensitive layers tend to be more sensitive.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  5. #5

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    Could'nt have put it better myself....

    Simon ILFORD Photo / HARMAN technology Limited :

  6. #6

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    Yeah, while I was laying awake last night it occurred to me that I did know, at one point, about the separate green and blue layers wrt VC and the filters. I've gotten so tunnel-visioned on the paper negative, staying away from the enlarger, that my brain is wiped clean. Thanks all! Going to be experimenting with targeted blue and green LED arrays for more efficiently lighting my indoor pinhole work.
    -brian hayden
    http://fed-2.org

  7. #7

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    Quote Originally Posted by Simon R Galley View Post
    Could'nt have put it better myself...
    HI Simon:

    Shouldn't that mean that when prinitng negatives with a blue tinted base with a neutal (2.5) MC filter, there would be proptionaltely less yellow light transmitted and thus more contrast in the final print?

  8. #8

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    It is often helpful to refer to an additive color wheel. The closer together two colors are, the more they allow eachother to "pass". Blue is not as effective at absorbing green light as colors in the magenta range. The blue tint in the film base would also have to be quite saturated/"strong".

  9. #9
    desertrat's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    It is often helpful to refer to an additive color wheel. The closer together two colors are, the more they allow eachother to "pass". Blue is not as effective at absorbing green light as colors in the magenta range. The blue tint in the film base would also have to be quite saturated/"strong".
    I've made contact prints of X-ray film negatives using VC paper and getting contrast filtration from the color head of an enlarger. The X-ray film base is pretty strongly blue, but it seems to have little effect on the contrast I get with recommended filtration. The contrast filters seems to work mostly as normal.
    Happiness is a load of bulk chemicals, a handful of recipes, a brick of film and a box of paper. - desertrat

  10. #10
    Thomas Bertilsson's Avatar
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    If you're referring to the Foma 120 films, there isn't enough blue in that film base to have a noticeable effect. The same is probably true for other films with a blue tinted base, although I personally know of no others.

    Quote Originally Posted by Pauken4 View Post
    HI Simon:

    Shouldn't that mean that when prinitng negatives with a blue tinted base with a neutal (2.5) MC filter, there would be proptionaltely less yellow light transmitted and thus more contrast in the final print?
    "Often moments come looking for us". - Robert Frank

    "Make good art!" - Neil Gaiman

    "...the heart and mind are the true lens of the camera". - Yousuf Karsh

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