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Thread: Platinum Dmax

  1. #11
    Photo Engineer's Avatar
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    Loris;

    After thinking about this, I was wondering if you were aware of a measurement called Goniophotometry. With this measurement, you can examine Dmax and tone scale as a function of viewing angle. You can observe many changes in Dmax or scale just by tilting the measuring angle.

    In another case, you can use a spot meter and a standard viewing method to measure the curve shape of a print of any kind. When you step back to viewing distance, a print with a Dmax of 2.0 can often fall to 1.8 just due to the way the spot meter sees the print and this is related to the reflectance as a function of viewing angle. It is, in simple terms, Goniophotometry.

    A densitometer gives you idealized results, but a spot meter reading a print as you would view it gives a human's eye view. Much of the time, these two results are quite different.

    PE

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    A meter with gonads... (?)

    Quote Originally Posted by Photo Engineer View Post
    Loris;

    After thinking about this, I was wondering if you were aware of a measurement called Goniophotometry. With this measurement, you can examine Dmax and tone scale as a function of viewing angle. ...

    When you step back to viewing distance, a print with a Dmax of 2.0 can often fall to 1.8 just due to the way the spot meter sees the print and this is related to the reflectance as a function of viewing angle. It is, in simple terms, Goniophotometry.

    A densitometer gives you idealized results, but a spot meter reading a print as you would view it gives a human's eye view. Much of the time, these two results are quite different.

    PE
    Does this mean a common 'spot meter' is a type of Goniophotometer?
    and that
    Goniophotometers read "angular" density
    while
    Densitometers reads "diffuse" density
    ?

    Do you have a picture of a Goniophotometer (?)

  3. #13

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    Quote Originally Posted by Photo Engineer View Post
    My own coatings, without overcoats and on Strathmore Smooth only achieve about 1.9.
    BTW,
    Which type of meter did you use to get a density of 1.9 with?

    As long as we are on this subject, can you clarify something for me?

    How can having a more reflective base (undercoat)
    and/or
    a more reflective surface (overcoat)
    increase D-Max?

    It would seem that the less light that got reflected... the higher the "density" would be... To me this is anti-intuititive.

    What am I over looking?

  4. #14
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    Yes and no.

    A spot meter can be used as a Goniophotometer if you can vary the angle of light or the angle of view.

    A densitometer can read several types of density but usually at only one angle (or group of angles) according to its design.

    There are some very good articles on Wikipedia on this Ray.

    I used Goniophotometry at one time to examine various tricks that could be played in surface reflection. I had 3 types of surface density as a function of angle, depending on tricks played. One was a rough ellipse, one was a rough circle (this is ideal BTW) and another looked rather like an onion with a pointy tip and a rounded body. It gave very high density when looked at straight down, but low densities off that angle.

    PE

  5. #15
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    Ray;

    I own a Kodak and a TRX densitometer.

    A more reflective undercoat implies a heavier and less penetrable undercoat with more imaging material on top thus giving more internal reflections and thus raising dmax to a point at which it is clipped.

    If the support is too thin or the white material is too thin, then light from the back can reduce Dmax, but if the surface is very impenetrable, then everything is on the surface with strong back lighting which gives (with ultra high gloss) a high dmax, as is seen in some very thin digital papers which are almost translucent but have everything essentially on the surface.

    Hold up a sheet of Endura or CA that has been fixed next to a sheet of almost any digital paper with backlighting and you will see how more translucent the digital paper is.

    They have less TiO2 or other whitener, and it is close to the surface with glazing materials incorporated and there is little paper in the RC sandwich. FWIW, they may not use TiO2 or RC. IDK, just that the sandwich is rather thin.

    PE

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    Quote Originally Posted by Photo Engineer View Post
    Ray;
    A more reflective undercoat implies a heavier and less penetrable undercoat with more imaging material on top thus giving more internal reflections and thus raising dmax to a point at which it is clipped.
    PE
    Maybe it's just too early for me, but all I was able to grasp was that with a more refelective base, more light is reflected, and this leads to more internal reflection which leads to more loss of light able to escape the photograph and reach our eyes... thus darker and greater densities.

    However, it would also seem that greater reflectivity would not only boost the amount of internal reflection (and thus light loss) but also at the same time the amount of light that does actually escape; The two would seem to counter balance each other.

    Rather than layers,
    are there are additives that can be added to an emulsion that,
    by increasing internal reflections, might increase density?

    As far as I know, matting agents at least, tend to reduce both contrast and density.
    Last edited by Ray Rogers; 07-13-2010 at 06:51 PM. Click to view previous post history.

  7. #17
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    Ray;

    If all of the emulsion is on the surface, less is reflected from the paper support. If it is half on the surface and half in the Baryta, then the dmax goes down, otherwise it goes up. But, it is a bell shaped curve so it goes up then down.

    Greater reflectivity can lower dmax and an example would be a very reflective RC paper in which the emulsion could not be absorbed.

    Additives are available to increase internal reflections. These are normally trimmer dyes to adjust speed and acutance dyes to adjust sharpness by reducing internal reflections. They are removed during the process.

    Matting agents do reduce contrast and density, but they are usually on the surface in an overcoat.

    PE

  8. #18

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    On Reflection...

    Quote Originally Posted by Photo Engineer View Post
    Additives are available to increase internal reflections.
    These are normally trimmer dyes to adjust speed and
    acutance dyes to adjust sharpness by reducing internal reflections.
    PE
    There may be additives to increase internal reflections,
    but I don't think they would be trimmer and acutance dyes

    As far as the rest goes however, I will just have to give it time to sink in I guess!

    Ray

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    The silver halide and silver metal formed during development are very effective materials that cause (or form the basis for) increases in internal reflection both before and after exposure.

    PE

  10. #20
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    Quote Originally Posted by Photo Engineer View Post
    If all of the emulsion is on the surface, less is reflected from the paper support. If it is half on the surface and half in the Baryta, then the dmax goes down, otherwise it goes up.
    Quote Originally Posted by Photo Engineer View Post
    If the support is too thin or the white material is too thin, then light from the back can reduce Dmax, but if the surface is very impenetrable, then everything is on the surface with strong back lighting which gives (with ultra high gloss) a high dmax...
    These two comments have got me thinking...

    With platinum there are no layers other than the Pt/Pd coating and the paper. Some of the coating soaks into the fibres of the paper whilst the rest remains on the surface; the amount that soaks in depends on the absorbency of the paper. And, of course, different papers have different thicknesses and degrees of whiteness.

    From what you're saying then, in order to get maximum Dmax one would need to use thick paper which doesn't absorb too much coating into its fibres. Am I understanding you right?

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