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  1. #11

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    Whenever the ASA standards were changed in the late 50s, the safety factor went from 2.5 to 1.25, so film speeds really did double at that point from one day to the next. I don't have a copy of my book handy but I refer to the one magazine author who has managed to get all the history right. The papers of Jones, Nelson and Simmonds from 1939 to about 1960 make clear everything one needs to know about speed evaluation, and make superb reading for anyone interested in this matter. It's some of the best and most practical research Kodak ever did. Sorry I don't have the exact citations handy at this moment. For anyone reading through those papers who is confused by the hump in the paper curve issue, Chuck Nelson cleared that up for me: it was due to an error in the measuring equipment, discovered some time after publication of the papers. The error doesn't affect the general validity of the work, which is absolutely solid. I really like those papers!

  2. #12
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    Bill;

    I'm glad you brought in this old but reliable information. Yes, the safety factor was still there and that is an important point. It did not vanish.

    And, film speeds did double due to supersensitization and so the final camera speed brought the actual image back to the same point on the curve.

    PE

  3. #13
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    Quote Originally Posted by Photo Engineer View Post
    Bill;

    I'm glad you brought in this old but reliable information. Yes, the safety factor was still there and that is an important point. It did not vanish.

    And, film speeds did double due to supersensitization and so the final camera speed brought the actual image back to the same point on the curve.

    PE
    Wait a minute, I guess I am confused. You say that the safety factor "did not vanish" and film speeds doubled "due to supersensitization" while Bill says the safety factor "changed from 2.5 to 1.5" resulting in a one stop increase in the ASA rating. It sounds to me like you two disagree with each other.
    Eddy McDonald
    www.fotoartes.com
    Eschew defenestration!

  4. #14
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    Eddy, earlier there were claims that speed doubled due to the fact that there was no safety factor. Bill has shown that there was a 2 stop safety factor that was reduced to 1 stop.

    So, a 100 speed film is now 200 with a 1 stop safety factor instead of 2 stops.

    Now, Kodak introduces supersensitization making it possible to have a 400 speed film (with safety factor). The previous argument would have it that the film had no safety factor.

    What was actually done was this. A 50 speed film became 100 (new measurement method), then 200 (super sensitizer) and then a dye was added to reduce speed to 100 but with much greater sharpness. This was done in both color and B&W products and yielded a big improvement in grain and sharpness both. And, it could be done generally as I stated before simply by changing addenda in the film. All of this retained a generous 1 stop speed safety factor.

    And actually, the supersentizer was far more potent than just 1 stop as I indicated in an earlier post.

    PE

  5. #15
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    Quote Originally Posted by Photo Engineer View Post
    What was actually done was this. A 50 speed film became 100 (new measurement method), then 200 (super sensitizer) and then a dye was added to reduce speed to 100 but with much greater sharpness. This was done in both color and B&W products and yielded a big improvement in grain and sharpness both. And, it could be done generally as I stated before simply by changing addenda in the film. All of this retained a generous 1 stop speed safety factor.
    Gotcha. I remember you talking about the two stop increase coming in two steps, but this last exchange had me confused. Thanks for the clarification.
    Eddy McDonald
    www.fotoartes.com
    Eschew defenestration!

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