Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,711   Posts: 1,548,659   Online: 1153
      
Page 5 of 5 FirstFirst 12345
Results 41 to 44 of 44
  1. #41
    Ed Sukach's Avatar
    Join Date
    Nov 2002
    Location
    Ipswich, Massachusetts, USA
    Shooter
    Medium Format
    Posts
    4,520
    Images
    26
    Photo Engineer,
    There seems to be something of a "shifting sea" in this exchange. If I discuss one aspect of color papers/ printing, something is introduced to deflect specificity to that particular subject.

    Photo Engineer,
    Going back to the original "set", I'll make a few SIMPLE statements:

    1 (a). Color Negative film is commonly structured with three light-sensitive layers: red-sensitive, producing a cyan image; green sensitive, producing a magenta image; and blue sensitive, producing a yellow image - ALL on a single "negative" base.
    This is not all-inclusive - there are other layers for various purpose - nor necessarily in any order.

    1 (b). Color Paper (I have to be careful here) for use in making "positive" images from negatives, is commonly structured with three light-sensitive layers: cyan sensitive, producing a red image; magenta sensitive, producing a green image; and blue sensitive, producing a yellow image. Again, in no particular order, and other layers may be employed for various purposes.

    2. In my experience, USUALLY only two dichroic filters are necessary in color printing: magenta and yellow. Occasionally more filtration is required, making the use of the cyan filtration necessary. By FAR the most common reason for cyan filtration is the mis-match between the source of illumination and the film color balance (Daylight, Tungsten, Type A, etc.), rather than some anomaly in the processing.

    Now... I may be dense, but one thing you have written makes NO sense to me, from any point that I read it:

    "Film speed for tungsten C<M<Y proportional to tungsten emission. This yields a neutral to tungsten light.

    Film speed for daylight C=M=Y (approximate) to daylight 'neutral white' emission. This yields a neutral to daylight."

    I'm not at all clear of what is happening here - C(yan) is less than M(agenta) is less than Y(ellow) and therefore something suitable for tungsten illumination (??), and C(yan) equal to M(agenta) equal to Y(ellow) is therefore suitable for daylight??? What is the significance of "equal to" and "less than"?

    I am even more lost in the, "Film speed for paper (should this be "paper speed" or "exposure sensitivity?) C<M<Y proportional to tungsten illumination + dmin of film + ~50R. This requires a piece of film (?) and about 50R to achieve a neutral to tungsten enlarger lamps.

    A "piece of film"? - ANY film?
    Carpe erratum!!

    Ed Sukach, FFP.

  2. #42
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    23,070
    Images
    65
    Ed, tungsten illumination is rich in the red region of the spectrum, less so in green and even less so in blue. Therefore, to achieve a so called neutral with nothing else intervening, the red speed is slower than green which is slower than blue. The blue speed must be fastest to make up for the low blue emission of tungsten illumination.

    This is good, because color negative papers have no yellow absorbing layer to protect the cyan and magenta layers from punch through of blue light. You see the cyan and magenta (red and green sensitive) layers are sensitve to blue light as well as to their primary region of the spectrum (red and green of course). But, since there is still a bit of punch through possible, the blue and green speeds are jacked up by the amount of speed equal to the punch through (about 50R worth) so that the filters in the beam remove the last residual element of punch through by knocking back this excess speed.

    In addition, since a color negative is going to be printed, and it has an orange mask, that amount of extra speed must be added to the blue and gree layers to offset the mask. (you can observe this by contact printing a perfectly balanced negative - you will see that the border of the negative reproduces as a light gray due to this effect.)

    In actual fact, the fundamental speed of color negative papers is judged by the speed of the cyan layer and the other layers are adjusted upwards from that point to achieve the goals above, namely 1. Approximate neutral from tungsten light, 2. +50R to remove any vestige of punch through, and 3. B and G speed bias approximaely equal to the dmin mask of average color negative film.

    In practice, the Cyan (red sensitive) emulsion therefore uses a 0.1 - 0.2 micron grain and the Yellow (blue sensitive) emulsion uses a 1.0 - 2.0 micron grain that is nearly film speed. Since we distinguish yellow detail poorly, the grain caused by this size difference is not easily seen.

    To see these effects, look at the wedge spectrograms of color paper published on the Kodak web site. The last time I looked, it clearly showed the Cyan and Magenta contamination of the Yellow due to punch through that is eliminated by appropriate filtration. If this is not done (ie by using cyan filtration) then this punch through can begin to show up in your prints. As you say, there are many reasons that one might need cyan filtration, but this does not mean it is what was intended by the manufacturere for optimum results.

    So, the piece of film is a piece of negative color film, processed but unexposed.

    PE

  3. #43
    Ed Sukach's Avatar
    Join Date
    Nov 2002
    Location
    Ipswich, Massachusetts, USA
    Shooter
    Medium Format
    Posts
    4,520
    Images
    26
    Quote Originally Posted by Photo Engineer
    Ed, tungsten illumination is rich in the red region of the spectrum, less so in green and even less so in blue.
    Please! There is no need to describe the spectrum form a tungsten lamp. I've done a fair amount of color spectrophotometry.

    So, the piece of film is a piece of negative color film, processed but unexposed.
    It would have helped to know that what you were talking about was the sensitivity to given wavelengths of light in the various layers.

    However, If the C<M<Y applies to emulsion layer speed, are you saying that C=M=Y indicates that all layers have the SAME sensitivity to daylight illumination?

    Also, Is Agfa's claim that exposure to naked enlarging lamp emission of 3000K - No filtration or "film" attenuation - resulting in equal exposure of all layers incorrect or --- ???
    Carpe erratum!!

    Ed Sukach, FFP.

  4. #44
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    23,070
    Images
    65
    Ed, the C=M=Y applies only to daylight film, assuming equal energy distribution. (Of course sunlight peaks in the green region at about 530 nm (I just have an approximate figure there) and so there is a slight discrepancy in actual practice).

    As for Agfa or any other color paper manufacturer, I would assume that either they are correct for their paper, or it is a simplification. To print well from the current population of color negatives, the ordering I described is a virtual requirement in order to avoid color contamination.

    The alternative places the yellow layer on top, and adds a yellow filter dye layer, thereby sacrificing dye stability and still begs the issue of printing with tungsten illumination and orange masked negatives. So, in the final analysis, the ordering of color negative paper speeds is C<M<Y to achieve all of the stated goals.

    This could concievably be done with a starting filter pack of zero (0,0,0), but then printing would be ever so much more difficult requiring a lot of calulation and zeroing out of neutral densities in the filter packs. So, all manufacturers have apparently done it the way I describe and you can add the goal of simplifying the printing step by only requiring 2 filters (M and Y).

    PE

Page 5 of 5 FirstFirst 12345


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin