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  1. #1

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    PMK VS Pyrocat-HD Stuff

    (Long and Technical)

    Recently I decided to do some tests with VC papers to provide some concrete information on a couple of issues regarding stained negatives about which there has been considerable speculation but little if any sensitometric data. Two questions were of interest to me.

    1. How will a stained negative that is developed to print on a #2 graded silver paper print on a VC paper using a #2 filter?

    2. Do PMK and Pyrocat-HD negatives print differently on VC papers.


    To answer the first question I selected negatives from previous tests of Ilford FP4+ film developed in Pyrocat-HD and PMK. The negatives selected had a CI of .52, when measured in Blue mode, which is about right for printing on silver graded papers in my conditions.

    To test this I first made contact prints with both the PMK and Pyrocat-HD negatives on a #2 Arista graded paper, exposing with the enlarger. The tests were developed in Ansco 130 1:2 for 2:30 minutes.

    The resulting prints were virtually identical when adjusted for the slightly higher density of the Pyrocat-HD negatives. I concluded from this that 1) when printing on graded silver papers the reading in Blue mode provides a fairly accurate indicator of paper printing scale, regardless of the color of the stain, and 2) there is little if any difference in the print regardless of which of the two developer one uses.

    I then made prints with these same negatives on Arista VC using a #2 filter, same conditions as above. Both prints were very flat and it became obvious that in order to print on the VC papers with the same contrast as on the graded paper I would need to either, 1) use a higher VC filter, or 2) use a negative of much higher CI. After some experimentation I found that a #5 filter was needed with the VC paper to match the result on #2 graded paper. Next I determined how much the CI of the negative would need to be increased so that the #2 graded paper would match a print on VC paper with a #2 filter. Again, after some experimentation I found that a negative CI of .70 was needed to print with the same contrast on VC paper using a #2 filter as a negative with a CI of .52 printed on graded paper.

    The curve for these negatives is attached. As you can see, the curves are virtually identical, even though the EFS of Pyrocat-HD at 125 is slightly higher than PMK, which bumps it up slightly on the y-axis.

    In order to answer the second of the two questions, i.e. do PMK and Pyrocat-HD negatives print differently on VC papers, I measured the densities of the prints made on VC paper #2 paper (using the PMK and Pyrocat-HD negatives with a CI of .70}. I then plotted the curves, which are attached.

    Examination of the curves indicates these differences.

    1. The PMK print has a *slightly* longer toe than the Pyrocat-HD print.
    2. The Pyrocat-HD print has a longer straight line.
    3. The PMK print shows a lot of shouldering, which indicates considerable highlight compression (or compensation).

    Persons who understand how negative curves correlate to print values understand that neither curve is superior to the other, though for a given type of film and/or lighting condition one might give better results than the other.

    Curves are characteristics of film developers. They are there to be used by people who understand them, but they don’t in and for themselves indicate that one developer is superior to another. But they do show important differences that will translate into differences in the tonal values of our prints.


    Sandy
    Attached Thumbnails Attached Thumbnails NegativeCurve.jpg   PrintCurve.jpg  
    Last edited by sanking; 12-31-2004 at 06:46 PM. Click to view previous post history.

  2. #2

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    Very interesting! Thanks, Sandy

  3. #3

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    Sandy,

    Could you label the axis of your graphs? Thanks - Kirk

  4. #4

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    Quote Originally Posted by Kirk Keyes
    Sandy,

    Could you label the axis of your graphs? Thanks - Kirk
    Kirk,

    Plain old H&D curve stuff. The x-axis, along the horizontal, corresponds to values of exposure expressed in relative logE values, which means that the numbers are in correct proportion to each other but do not corresopond to any specific standard of measurment. The y-axis, on the vertical, relates to values of image density, also in log values, that corresond to the common log of opacity.

    Sandy

  5. #5

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    Thanks Sandy. Always useful to see something in concrete!
    Tom

  6. #6
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    Sandy, thanks for posting these tests. Would the toe of the PMK print be one relative difference in the "muddiness" of a PMK print (like comments on the azo forum) when compared to Pyrocat, with respect to shadow detail? That extra little bit of speed in Pyrocat formula seems to be one factor in the shadow detail being more open and full.

  7. #7

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    Thanks Sandy. Trying to get my head around this by putting this in real life situations; I would assume that both PMK and HD are equivalent for low contrast situations where there are mostly middle tones (ie caucasian portraits or a cloudy day in the woods where shadow contrasts are lacking).

    Where these two seem to differ is where the contrast and range of tones at the ends need to be more separated (example slit canyons at mid morning, where sunlight is strong at top of slits, yet still dark at bottom). IT would also appear that HD would not have as much pure black or pure white in a print compared to the PMK print which may or may not be desirable.

    PS Thanks for continuing to share your knowledge here and elsewhere.
    Eric
    www.esearing.com

  8. #8

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    Sandy,

    Thank you for your work on this. The contrast difference graded to VC materials is of particular interest and parallels my actual printing difference in the darkroom. My results have indicated that the densities Ansel Adams proposed in "The Negative" no longer apply in my printing with my materials (Forte and Oriental graded, and VCFB).

    As I read your curves they indicate that Pyrocat does offer better tonal separation throughout it's curve by virtue of the shorter toe and the absence of the shouldering indicated with PMK.

    Did you do any work on the issue of stain color in the compression of highlight tonal scale between PMK and Pyrocat when used with VC materials and the effects of the stain color as it effects the colors of VC filters?

  9. #9

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    Hello Sandy,

    From this observation...

    "Again, after some experimentation I found that a negative CI of .70 was needed to print with the same contrast on VC paper using a #2 filter as a negative with a CI of .52 printed on graded paper."

    Would I be foolish to now make the assumption that this would be similar for all VC papers?

    I am also curious as to why there is such a dramatic difference in the CI required when printing on VC paper. Would you be able to explain this in simple terms or perhaps at least speculate on the possible reasons?

    When you printed on the graded paper would it be correct to assume that you were using your enlarger light source without any VC filters in play and as such used that as your baseline for a #2 graded paper?

    If so... how different would you speculate that the color output of your enlarger is without filters, is in relation to your enlarger with a filter in place to print a #2 VC paper?

    My personal experience with my enlarger (Saunders 4500) is that with VC paper I print approximately one grade harder without a filter as I do with a #2 Ilford filter in play. In other words...I must use a #3 filter to closely approximate a print that would otherwise print the same (time adjusted of course) without any filter being used.

    I am just surprised by the the extreme difference that you are reporting in CI from a graded paper to a VC paper.

    Kind Regards,
    Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

  10. #10

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    Quote Originally Posted by GreyWolf
    I am just surprised by the the extreme difference that you are reporting in CI from a graded paper to a VC paper.

    Kind Regards,


    I was not especially surprised by the very large difference for the CI requirements of graded and VC papers because it is consistent with observations and examples made by Barry Thornton in the Edge of Darkness, which also show a difference of 2-3 grades. However, since some people have reported less of a difference there may be a variety of factors in play that need to be explored in more detail, including the type light in the enlarger, type of VC filters used, different spectral response of papers, etc.

    So in that respect it may be useful to state all of the factors in play in my testing. Here is what I used for the test. My exposing light is a Beseler 23-C enlarger with the standard incandescent bulb (Wiko PH/111A, 125V75W). When I printed on the graded paper I did not use a filter. For the VC tests I used the Kodak Polymax filter set. The #2 filter is amber in color, while the #5 is strongly magenta.

    As previously noted, the papers that I used were Arista, a graded #2 paper, and Arista VC paper. I did not verify if there was any difference in contrast with the VC papers in printing with a #2 filter and without it, though from past experience I know that if there is any difference it is quite small.

    Sandy
    Last edited by sanking; 01-01-2005 at 03:01 PM. Click to view previous post history.

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