Densitometer readings?

Discussion in 'B&W: Film, Paper, Chemistry' started by Jim Fitzgerald, Oct 30, 2007.

  1. Jim Fitzgerald

    Jim Fitzgerald Member

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    Let me first say that I do not know much if anything about this machine but I'm willing to learn. I guess I'm more of a Weston type. It works like magic and I don't know how. I have a Xrite 329 densitometer. I read my Pyro negs on the blue channel and here are some of the reading I've gotten. These are my first 8x20 negs and I'm trying to figure out how this relates to my printing paper. I have one neg that is good to my eye. It is Bergger 200 shot at 80 and developed in Pyrocat HD in trays for 12 1/2 minutes at the 2:2:100 dilution. The readings are .87 and 1.92. Is the range DR 1.05? I have no idea how this relates to my paper that I'm trying to contact print this on which is Forte Polygrade V. I know there are many questions the people who know about all of this have for me. So fire away. I know this film is not the best to expand contrast. Would I just increase the development time? I have another test negative that I developed for 16 minutes and the readings are from 1.35 to 1.68? The exposure for this neg was about 2 1/2 minutes and I should have reduced development probably. How do I find the paper curves to match the neg to? Am I backwards in my thinking? Like I said I'm interested in learning but I'm a slow learner so be patient. Help me understand the process. This is something I've always been curious about but I need a simple explanation. Thanks to all.


    Jim
     
  2. gainer

    gainer Subscriber

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    Were I in your shoes I would contact print the two areas you measured with small pieces of the paper you plan to use. The blue channel readings would be more appropriate for graded paper, but sample prints on the Polygrade will help you calibrate your densitometer. OTH, maybe I'm all wet in assuming that Polygrade means variable contrast.

    The problem with the densitometer is that you need to make a print in order to calibrate it! The value of the densitometer is that once you have it calibrated, you can apply some factors that will let you read the DR next time, but if you are using variable contrast paper, the factors will vary with the printing filtration, so you may need a chart of meter factors vs filter setting or filter number.
     
  3. Marc .

    Marc . Member

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  4. Jim Fitzgerald

    Jim Fitzgerald Member

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    Pat, thanks for the response. This has always interested me. The Forte Polygrade V is a variable contrast paper. I have done some Azo prints that I can measure along with some Kentmere graded prints. So, when I measure the prints what channel do I use? Then when I compare the print readings to the negative readings how do they relate? I hope this makes sense? I'm sure I'm confused but that is normal for me.

    Jim
     
  5. Jim Fitzgerald

    Jim Fitzgerald Member

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    Marc, I think reading and research is the answer. Thanks.


    Jim
     
  6. Photo Engineer

    Photo Engineer Subscriber

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    The zone system is only 7 points on a 21 point scale. Each zone is 1 stop from the adjacent steps. The complete 21 point scale is encompassed by a normal film with a range of density from 0.1 to 3.0 under normal conditions. The slope is about 0.6 for negative films.

    Paper has a range of 0.1 to 2.0 under the same conditions and as a negative, it has a slope of 2.5 (grade 2) and 1.5 as a print.

    So, the zone system is a small subset of the H&D curve and a small subset of the full range of a film.

    PE
     
  7. Jim Fitzgerald

    Jim Fitzgerald Member

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    Ron, thanks for this. Let me digest it a bit so I understand. I think a step wedge is in order so I can "see" what is going on and how it relates. Sorry for being thick headed but some of this stuff confuses me. I appreciate your expertise and knowledge in these areas.


    jim
     
  8. Marc .

    Marc . Member

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    Jim,

    Here is also a link to a Kodak workbook on sensitometry (this is the name of the thing...)
    http://www.kodak.com/US/plugins/acrobat/en/motion/education/sensitometry_workbook.pdf

    Phil Davis' book covers the same subject, explaining each concept and suggesting exercises.

    The effort to read these books is well worth it !

    Best,

    Marc
     
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  9. Curt

    Curt Subscriber

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    I have a Macbeth densitometer and a Stouffer calibrated scale so I can make sure the densitometer is reading correctly. In the back of the book "The New Zone System Manual" White - Zakia - Lorenz, is an excellent explanation relating the paper to the film and both to the Zone System. In the Appendix, I, Calibration with Densitometer and Graphs explains step by step how to take measurements and plot the curves, very nice to know for contraction and expansion. Flair, reciprocity and other topics that come into play are also covered. It's a book well worth having.

    Stouffer site: http://www.stouffer.net/TransPage.htm

    Curt
     
  10. Photo Engineer

    Photo Engineer Subscriber

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    The Kodak reference is excellent. It explains the whole thing in detail.

    I used to think (with no derogatory thoughts intended) that the zone system was densitometry and sensitometry for dummies.

    Sorry. My failing entirely!

    PE
     
  11. gainer

    gainer Subscriber

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    We have two different considerations. I do not remember from what I have seen of BTZS that the problem of relating densitometer readings to paper response was addressed for pyrogallol or catechol stained negatives printed on VC paper, where the ratio, so to speak, of blue to yellow has an effect on the contrast of the paper response. I have not found, after considerable effort, a way to go from densitometer readings of stained negatives to choosing the proper VC filtration to fit the scale of the negative. I have designed and built my own projection densitometer with two adjustment dials, one for slope and another independent one for level. I should be able to set those two scales to match any filter from a set or any dial setting on a color head, but there is still the unknown of the ratio of stain image to silver image and how that ratio interrelate the color sensitivity of the densitometer with the response of the paper. Sooner or later you will have to make up some tables, and there will be at least one for each developer, each film, each filter or filter setting of the enlarger, and all this to take the place of some simple test strips, which you will either have to do for corroboration or risk a large sheet of printing paper on the basis of a densitometer reading.
     
  12. Jim Fitzgerald

    Jim Fitzgerald Member

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    Pat, I see that my curiosity could get very time consuming with testing. Maybe I'm better off just wondering about this stuff and be more concerned about exposing negative and just printing them! Thanks for your help.

    jim
     
  13. gainer

    gainer Subscriber

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    P.S.
    IIRC, the Zone system was a musician's (and a very fine one's) way of comparing the visual tone values in a scene to an octave from no sound to inaudibly high sound. Most fine musician's I have known have some innate mathematical sense. Some have been professional mathematicians as well, and others in other technical fields. Some of them would say I was one of them. The complexity of Zones in fractions other than half tones is, I think, the product of other than musical minds.
     
  14. Jim Fitzgerald

    Jim Fitzgerald Member

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    Pat, this is a good analogy. I can relate. Although I'm challenged with math my three sons are not. They are all three very fine pianists. They have performed with symphony orchestras as soloists. My oldest and most gifted was told by a conductor during a rehearsal for a performance of Beethoven's Emperor Piano Concerto how precise his timing was. It was just part of who he is. It is a very demanding piece for a 17 year old and thankfully I have the CD of this astounding performance. I do believe math and music go hand in hand. Must be why I turned to photography! Could not get the music thing going.

    Jim
     
  15. Jim Fitzgerald

    Jim Fitzgerald Member

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  16. Jim Fitzgerald

    Jim Fitzgerald Member

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    Curt, the book seems to be what I'm looking for . Thanks.

    Jim
     
  17. Ray Heath

    Ray Heath Member

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    hey Jim
    why not just make a print and visually appraise the result

    Ray
     
  18. Photo Engineer

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    There are two important difference here that must not be forgotten.

    1. Density is always in a visible range, not from invisible (0) to infinitely high. This is not within the reach of todays films (or digital) products. The lowest finite density is about 0.1 and the highest film value is about 3.0, both well within the visible capability of a single scene.

    2. Half tones or less than half tones are not used in film. The 21 step scale is measured in stops and half stops which are real speeds on the camera. These steps attain in any image and the only variable is the shifting of the ISO range of a given film within which something is photographed. Thinking in less than stop or half stop changes is not common, but thinking in a continuous density scale is quite within the range of common practice in analog photography, if not in digital.

    PE
     
  19. Photo Engineer

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    I should amend the above regarding tones and half tones to exclude the dot processes of halftone images which are not within the scope of this. It is an entirely different matter than should not be misconstrued to be included in either my comments or Patricks.

    PE
     
  20. Jim Fitzgerald

    Jim Fitzgerald Member

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    Ron, I am truly amazed by the depth of knowledge that you and Patrick and others on this forum have and are willing to share. You give me a lot to think about and ponder. Thank you so much for that.

    Jim
     
  21. gainer

    gainer Subscriber

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    Yes indeed. I was thinking of the fact that we might read the densitometer to 0.01 or less density increment which might translate on the calculator or slide rule to a small fraction of a Zone. Some who slip into that usage should remember that when you encounter less than half a tone in music it is a serious mistake, a passing tone in a glissando on a stringed instrument, or some soon to be forgotten experiment in modern music. Not in any case any sound that would come out of Ansel Adams' well tuned piano.