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Thread: Why 160?

  1. #21
    Jesper's Avatar
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    160 Asa as we think of it today may be strange for us, but it is 23DIN.
    Is 23 more or less logical than 21DIN (that is 100Asa) or 27DIN (400Asa)?

  2. #22

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    To make film faster, the sensitivity has to increase exponentially, i.e. one step difference means doubling the sensitivity. In reverse, it decreases logarithmically. A similar thing happens with music. If you look at the neck of a guitar, the frets aren't spaced evenly, they get further apart the further from the body you go.
    100-200-400-800-1600 are the major steps, but each step has half and third steps between it and the next one. Because the scale is exponential, a third of a step isn't 0.33, and changes throughout the step. The difference between 100 and 125 is the same as between (125 and 160) and (160 and 200) and (400 and 500) and (5000 and 6400). These aren't exact figures because the actual figures are horrendous irrational numbers, but 160 is a lot easier to remember than some awful and negligibly different surd.

  3. #23

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    I've always wondered this too...

    And also, I've never (that I can recall) seen ISO 200 120 rolls. Do they exist?

    EDIT: Well explained Mattmoy, makes much more sense to me now!
    Currently shooting: KMZ Horizont and Minox B

  4. #24

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    Quote Originally Posted by Mike1234 View Post
    Wouldn't 141 speed be closer to the middle of 100 and 200?
    It would be the exact middle between 100 and 200. But ISO speeds typically go in 1/3 stops rather than 1/2 stops. So you are more likely going to see ISO125 or ISO160 than ISO141.

    Quote Originally Posted by Chris Nielsen View Post
    If clocks go clockwise because of the sundial and sundials run anticlockwise in the southern hemisphere, then clocks down here should run anticlockwise as well, shouldn't they?
    Maybe if clocks were invented in the Southern Hemisphere.

  5. #25
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    Quote Originally Posted by Blacknoise View Post
    I've always wondered this too...

    And also, I've never (that I can recall) seen ISO 200 120 rolls. Do they exist?

    EDIT: Well explained Mattmoy, makes much more sense to me now!
    What about E200?
    www.EASmithV.com

    "The camera is an instrument that teaches people how to see without a camera."— Dorothea Lange
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    RIP Kodachrome

  6. #26
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    Maybe 160 is a nicer number than 200.
    Since 160 looks more like 100 than 200, it gives a different thinking about the film; Less grain, more sharpness...

    Just like when prices are 9.95/9.99 instead of 10.

  7. #27
    mts
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    To remind you to rate it at EI-125.
    By denying the facts, any paradox can be sustained--Galileo

  8. #28

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    Sixty years ago color films used to be ASA 12. Just be glad you have 160.

  9. #29

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    The Kodak portrait color negative films have slowly gained speed through the years. Ektacolor Professional S (C-22) and Vericolor S (C-41) were ASA 100. Vericolor II Professional S was ASA 125. Vericolor III was 160, as is Portra 160NC (of course). So it gained speed a third-stop at a time over the last 35 years.

    Of course, with Portra, they also added 400 speed films, and later an 800 speed.

  10. #30

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    Box speeds are based on log density vs exposure etc. , but they are still basically ballpark figures and the shooting speed depends on the look you want and the way you meter the scene. With colour neg film it's best to lean towards overexposure rather than under exposure. Combine that with most in camera meters being optimized for slide shooting, and 160 allows you to to comfortably rate the film at 100 -125 and have a good margin for exposure error and reasonable sharpness when hand holding. Whereas at 100, you might want to rate your film at 64 which is getting a little slow for taking pictures of people which is what the 160 speed portrait films are primarily intended for.

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