HD Characteristics for Ilford MGIV RC and FB

Discussion in 'Darkroom Developing and Printing' started by Nicholas O. Lindan, Dec 7, 2006.

  1. I have posted paper speed data - also known as HD curves -
    for Ilford MGIV RC and Fiber base papers at:

    http://www.nolindan.com/da/support/

    Although meant primarily for Darkroom Automation's customers
    the data is of general interest and utility.

    Interesting points I find in the data are:

    o For each paper some contrast filters have almost
    identical effects

    o The paper response is quite different between the
    RC and the FB paper.

    The X-Axis on the curves is in stops of exposure using
    Darkroom Automation's EV system for determining paper
    exposure and contrast.

    stops of exposure = EM1003 Precision enlarging meter reading +
    Darkroom Automation f-Stop Timer setting

    and can be recalibrated to log10 exposure by multiplying by
    0.3.

    More information on the Darkroom Automation EV system can be
    found at:
    http://www.nolindan.com/da/em/eminstructionsi.pdf

    The system can be use with any sufficiently accurate darkroom
    exposure meter.
     
    Nicholas O. Lindan, Dec 7, 2006
    #1
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  2. Very interesting. I have seen manufacturer's published curves for
    someVC papers which showed that highlight contrast varied very little
    or not at all for different filters. Your curves look more like those
    for graded paper, good to know.
    Have you experimented with other surfaces at all? The reason I ask
    is that at one time Kodak published a chart showing the effective
    contrast range for the full range of variable contrast filters for
    three or four surfaces available at the time. On glossy paper (this is
    RC) each filter made a difference. For matt surfaces several adjacent
    filters were exactly the same. It appears that both Dmax and contrast
    can be significantly reduced by surface texture.
     
    Richard Knoppow, Dec 10, 2006
    #2
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  3. Nicholas O. Lindan

    nolindan Guest

    If an HD curve is replotted so that AA's Zones are on the vertical
    axis (The LA graph?) something interesting happens:

    http://www.nolindan.com/da/support/mgivrczones.jpg

    Suddenly the various contrast curves become linear and fan out
    into some sort of sensible equal-interval order. Note the curves
    are normalized to the mid-grey Zone V which is nominally pegged
    at 0.70OD or 20% reflectance.

    I think this explains why the Darkroom Automation exposure system
    works so well: the system works in zones Vs stops of exposure -- the
    system works with the table of data used to generate the
    mgivrczones.jpg
    graph. Just looking at the HD curves for a paper and one's rational
    instinct is to have nothing to do with it when making a print.

    This straightening of paper HD curves is what is to be expected.
    Adams drops the zone system when it comes to printing,.The
    derivation of the zones - ref. page 86 of 'The Negative' 1981
    edition - is by plotting zones on the X-Axis, where zones are one
    step apart and density on the vertical axis and then declaring the
    density of zones to be the HD curve's values at one stop intervals.
    printed at that density. The zones are not placed to be 'visually'
    correct at even intervals.

    There is quite a visual difference at the light end of the scale
    between a reflection density step table and a print of a transmission
    step tablet. In the print there are lots of nice light delicate greys
    with which to make highlite detail. In the reflection tablet things
    go from dead white to medium grey in the first step.

    At the dark end the difference is far less apparent as by the time
    the shoulder is reached in the print everything looks pretty black
    and the difference between 2.0 OD and 2.5 OD is well nigh invisible.

    When the toe end of the curve is straightened by using Ferricyanide
    bleach things get interesting -- the highlights become much more
    brilliant but it seems to take a special negative to maintain detail.
    Adam's "Vernal Fall's" is, to me, the epitome of brilliant highlights;
    I have an original print of it hanging in my office and one day
    I will figure out how he did it.

    One conclusion - you can't get highlight detail by bleaching
    RC paper - the three emulsions in the paper bleach at different
    rates and highlights turn to a warm-beige color. As a result
    the whole thing just looks like a faded print, which in a way it is.
    Yes... You have no idea how much fun it is, exposing step tablets
    and sitting in front of a densitometer all day ... For every paper,
    every surface, every grade, with highlight bleaching, with latent image
    shadow bleaching, with toning.
    That does happen.
    Lots. The old N(?) suede surface is gone. It's purpose was to hide
    wrinkles in portraits of old ladies, as near as I can tell: no
    contrast,
    no wrinkle.

    Posted via google, as netcom/mindspring/earthlink has broken
    it's link with the earth, sprung it's mind and is no longer
    communicating
    with the net.
     
    nolindan, Dec 12, 2006
    #3
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