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Thread: F1.8 vs F3.2

  1. #1
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    Default F1.8 vs F3.2

    Say I take a 1s shot using F1.8. How many seconds would it take for a F3.2 lens to get the same level of exposure? Are there any formula I could use?
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  2. #2
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    I'm sure there's a complex mathematical formula somewhere, but use the following table until someone coughs it up:

    f1.4
    -- f1.6
    -- f1.8
    f2.0
    f2.8
    -- f3.2
    -- f3.5
    f4

    Each figure on the left column is a full f-stop, while the indicated figures on the right at the universally accepted (for convenience) 1/3 stops.
    So f1.8 is 1 and 2/3 stop faster than f3.2, hence you should use that amount a lengthier shutter speed, or 3s.
    Last edited by Jed; 20th January 2002 at 03:31 AM.

  3. #3

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    f/3.6 will be 2 stops faster than f/1.8, so f/3.2 will be slightly less than 2s?

  4. #4
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    No, two stops away from 1s is 4s (1s, 2s, 4s, 8s, etc.) So it's slightly less than 4s.

  5. #5
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    Thanks guys for enlightening me!

    So, roughly every "1.414" times is one stop loss in light requiring doubling of the exposure time right?
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  6. #6
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    Yes that's right. Cause apertures are measured as a reciprocal ratio of the diameter, area wise. Hence the number is achieved by a root of two, which is 1.414 etc as you point out.

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