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Thread: How To Understand Densitometer Readings

  1. #11

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    Re: How To Understand Densitometer Readings

    Quote Originally Posted by Greg View Post
    Highly recommend the following book:

    Photographic Sensitometry: The Study of Tone Reproduction
    by Hollis N. Todd, Richard D. Zakia | Hardcover

    You can easily find a copy up for auction for $5-10.00. When I was at RIT, became good friends with Hollis Todd. The book at first seems overwhelming at first but once you skim its contents, it becomes easy reading.
    +1!!!

  2. #12

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    Re: How To Understand Densitometer Readings

    Quote Originally Posted by IanBarber View Post
    Are there any charts that map densities to zones ?
    Here's a screenshot of a table from Way Beyond Monochrome Ed.2:

    Click image for larger version. 

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  3. #13

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    Re: How To Understand Densitometer Readings

    Quote Originally Posted by IanBarber View Post
    Are there any charts that map densities to zones ?

    First see here pare 10 and 11 of the file pointed byMichael file:///C:/Documents%20and%20Settings/P.PC6/Escritorio/PS/US_plugins_acrobat_en_motion_education_sensitometry_workbook.pdf

    In ISO conditions (standard development for ISO), if ISO Speed is 100 then Zone V has a density Base density of base + 0.72, every zone you move up or down it has a constant density shift, an exposure step (a zone) is twice the light, so in the Hor log scale it moves 0.3 units, the density increase/decrease it would be 0.3 * curve stepness this is 0.3 * 0.6 = 0.18, so (with standard ISO development) every additional zone moves 0.18D.

    It also happens with other ISO speeds, curve is has the same stepness, so ISO norm says that Zone V has a density = 0.72D + film base density. Film base density is the one of the areas that received no light. Add/Substract aprox 0.18D for each additional zone.


    But this depends on your development (that cannot be the same than ISO norm)... and it is related to Scene Zones, not to print zones. In fact you can place a Zone of the scene in another zone of the print...

    I think I'm not mistaken, other users should review that.


    Regards


    PD: edited to replace 0.9D by 0.72D, it was a great mistake
    Last edited by Pere Casals; 20-Oct-2017 at 06:22.

  4. #14

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    Re: How To Understand Densitometer Readings

    Quote Originally Posted by Jerry Bodine View Post
    Here's a screenshot of a table from Way Beyond Monochrome Ed.2:


    [/COLOR]
    Click image for larger version. 

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    PD: here I was is wrong.

    Hmmm, I don't understand why Z-V do not says 0.9D + base (This is Way Beyond Monochome book !!!)




    https://en.wikipedia.org/wiki/Film_speed


    "Speed point" is at 0.9D over base (0.8+0.1), since year 1960.

    This table shows speed point in Z-VI, instead Z-V ....

    Until I know photometers aim "n" point in the graph...

    Do the photometers aim to "n" point ?

    Do the photometer aim to Z-V ?
    Last edited by Pere Casals; 20-Oct-2017 at 06:19.

  5. #15

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    Re: How To Understand Densitometer Readings

    Pere - point n is not the metered exposure and is not Zone V.

  6. #16

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    Re: How To Understand Densitometer Readings

    Quote Originally Posted by Michael R View Post
    Pere - point n is not the metered exposure and is not Zone V.
    Hello Michael,

    You are right... I was mistaken.

    Please look this chart:



    We dicussed that in this thread: http://www.largeformatphotography.in...=1#post1395912


    Point (4) is the ISO Speed point.

    Point (5) is at 10x more lux than Point (4), at it is the point where meters are calibrated for the rated speed resulting from the graph.

    So 10x is 2.3 stops or zones, and +1H

    IMHO Zone V is at point (5) ,

    Then... where "n" point is? It should be at +1.3 H, at the right of Point(4).

    So "n" point is 0.3H at the right of Z-V point, and this is an stop.

    So the "n" calibration point is one stop overexposed from the meter reading point.


    In the past (before 1960) n point and meter point were the same point, but norm changed in 1960, ASA PH2.5-1960 simply mutiplied speed of all existing films by 2.

    Is because this that there is exactly one stop from n point to the meter point.

    Regards.

  7. #17

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    Re: How To Understand Densitometer Readings

    The metered exposure is 1 log H (3 1/3 stops) to the right of Hm. Point n is 1 stop higher.

  8. #18

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    Re: How To Understand Densitometer Readings

    Quote Originally Posted by Michael R View Post
    The metered exposure is 1 log H (3 1/3 stops) to the right of Hm. Point n is 1 stop higher.
    This is, exactly 1 stop. I was wrong.

  9. #19

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    Re: How To Understand Densitometer Readings

    Quote Originally Posted by IanBarber View Post
    Thanks Michael, I shall investigate that link you sent.

    At this stage, I guess I am more interested to make sure I have enough density in the shadow areas to reveal some texture. I have read that Zone 1 is 0.1 above film base and fog so I am guessing that Zone 3 should be about 0.9 above film base and fog but I could and are probably wrong there
    I don't think it necessarily works out that way. Zone 3 film density is the negative density that results when the film receives a Zone 3 exposure and then developed at "Normal" development.

    Determining "Normal development" requires some testing. Indeed, you first determine THE ASA that places a Zone 1 exposure on the film at 0.1 density units above fb+f. Then based on my past testing, Normal development becomes that length of development time such that a Zone 8 exposure on the film yields a negative density of 1.35 density units with the light meter set at the above ASA.

    Just to clarify, a Zone 1 exposure is 4 stops darker than the light meter reading, a Zone 3 exposure is 2 stops darker than the light meter readings, and Zone 8 exposure is 3 stops brighter. (e.g. determine the aperture and shutter speed on an area to expose using a light meter, and before exposing, open the aperture by 3 stops.
    Last edited by neil poulsen; 26-Oct-2017 at 05:47.

  10. #20

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    Re: How To Understand Densitometer Readings

    There's little interesting information in Zones 1-3, I'd be more concerned with getting the Zone VII exposure (1.15 above fb+f) correct. There are entire books written on photographic sensitometry, it may be worthwhile reading. One was referenced above. Also I assume that Neil's post above supposes that you are using a spot meter, otherwise, all bets are off. If you haven't already done so I'd get the Zone VI Workshop by Fred Picker.
    Last edited by Luis-F-S; 25-Oct-2017 at 16:10.

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