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  1. #41
    ic-racer's Avatar
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    After reading through this thread I think the title might be better phrased as "Enlarger -> Control Strip Maker"

    I think the work 'sensitometer' is too vague for the discussion. The word sensitometer includes a variety of instruments from the enlarger PE uses to a mammography department's control-strip maker to a Harvard-Smithsonian tube sensitometer calibrated to an Eppley standard lamp powered by an Eppley standard precision power supply wired in series with a precise 0.1ohm resistor.

    The majority of sensitometers on the market are basically control-strip makers. They are very useful tools used to answer common practical questions about processing and used to provide important relative speed information.

    The utility of a device for determination of absolute film speed in a home darkroom is zero as far as I am concerned. I can read the number on the film box just as well as anyone. Even if one did have such an instrument and appropriated calibrated lab in which to use it, how would you interpret your results if, for example, Ilford Delta 100 came out faster or slower than 100? Bad film? bad film company? bad calibration? bad day in the lab ?

  2. #42
    Stephen Benskin's Avatar
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    Any good precision testing device tends to be very expensive, and there's always something better for an exponentially higher price. I have what I believe to be an expensive scientific testing device. I'm very proud of my sensitometer, but some guy at Kodak saw it as a toy. My point isn't that people need to use precision equipment or strive for absolute accuracy with their testing. It's that they should be aware of limitations of any test. Go ahead and do a film test with an enlarger, but be aware of the variables, tolerances, and variance. Don't assume the results are absolutely correct (not that they need to be) just because you call what you did a test. Like for example some of those who do Zone System testing and believe they've found the "true" film speed and their results are superior to the manufacturer. The key is understanding the reason for the test. Don't just follow some step-by-step instructions without question. Ask and understand why. Know your theory.

    If Leigh B is raising the question I believe he is (which would make for a great discussion), I would have to say if I had to make a choice between a test that would produce only one of two possibilities either an accurate film speed or a characteristic film curve that eliminates as many variables as possible so that it can best represent the way the film responds to exposure and development, I would pick the curve without hesitation.

  3. #43
    Photo Engineer's Avatar
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    Well, I have been using my enlarger for several years now.

    I have first calibrated it in terms of exposure (time, f stop and color balance) and then I embarked on a project to make internegatives from my slides using Portra nC in a pulled process. The results are quite good and quite repeatable. So, I have no quibblles with my enlarger, once calibrated.

    PE

  4. #44
    Leigh B's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    Maybe you should explain how you test.
    I shoot a step tablet against a neutral gray background, using a camera and a lens.

    I don't take pictures with an enlarger. Why would I test film using one?

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  5. #45
    Stephen Benskin's Avatar
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    Quote Originally Posted by Leigh B View Post
    I shoot a step tablet against a neutral gray background, using a camera and a lens.

    I don't take pictures with an enlarger. Why would I test film using one?

    - Leigh
    Just to be clear. You shoot the step tablet in front of the lens using a gray background as the background light source. Is the tablet masked in anyway?

  6. #46
    Leigh B's Avatar
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    I don't understand "background light source". The tablet is illuminated from the front, about 45°, with diffused lighting.

    What do you mean by "masked"?

    The purpose of the neutral gray background is to produce a negative of average density so the developer activity is normal,
    not overly concentrated nor exhausted during development.

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  7. #47
    Stephen Benskin's Avatar
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    So you are shooting a reflection gray scale then?

  8. #48
    Leigh B's Avatar
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    Yes. My photographic subjects are reflective, therefore my test subjects are reflective.

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  9. #49
    Stephen Benskin's Avatar
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    Thanks.

  10. #50
    Bill Burk's Avatar
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    When the EG&G first arrived I read the manual and started marking corrections where I was right and the manual was wrong...

    Where it said ASA 133 was -3.78 MCS I scratched out and wrote -2.22

    Took me a while to realize how bar notation works: characteristic -3 and mantissa .78

    We were both right, in traditional log notation "bar 3.78" is the same as calculator notation "-2.22"

    ---
    Now I am not looking to keep a 1 metre bar of platinum in my garage for reference.
    ---
    But I do have a puzzle to work out where I need to know absolute speed "of something".

    Assuming fresh TMY-2 gives me 400 speed in D-76 1:1... relatively speaking, I get 50 to 64 speed from expired Panatomic-X in D-76 1:1

    So my puzzle is:

    Am I not really getting full speed from TMY-2? (Perhaps D-76 isn't the prescribed developer).

    My D-76 was mixed 4/19/12 - maybe it is "more active" now?

    Or the counter-intuitive, but possible, reality... Does slow film get "faster" when it ages?



 

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