Film speeds- arbitrary numbers?

Discussion in 'B&W: Film, Paper, Chemistry' started by joshverd, Jan 20, 2007.

  1. joshverd

    joshverd Member

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    Hello,

    I'm interested to know if there is any mathematical relationship between film rating and f/stop / shutter speed combinations. Why is 200 speed film called 200?

    We all know how to expose them, we just punch numbers into our light meters. But, are these numbers arbitrary or do they give insight into film sensitivity in some way other than our accepted conventions? I imagine there is some historical reason.

    Also, how does one find the "actual" speed of the film? Is it just by visual assesment, or is there some way to do it with densitometry, etc...
     
  2. jstraw

    jstraw Member

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  3. jim appleyard

    jim appleyard Member

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