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Thread: f-stop trivia

  1. #1
    david b's Avatar
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    f-stop trivia

    In an effort to win a bet with a friend, who can name the stops between:

    f2.8
    f4
    f5.6
    f8
    f11
    f16
    f22

    (ie. what is the stop between f16 and f22)

  2. #2
    Sportera's Avatar
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    In half stops?

    3.5
    4.5
    6.8?
    9.5
    13
    19

  3. #3
    ann
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    how about
    3.5
    4.5
    6.3
    9.5
    12
    18

    between 16 and 22

    18
    20
    Last edited by ann; 07-14-2006 at 09:04 PM. Click to view previous post history. Reason: additon
    http://www.aclancyphotography.com

  4. #4
    ann
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    oops, sam already gave half stops.

    do you want thirds, lol
    http://www.aclancyphotography.com

  5. #5
    Helen B's Avatar
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    If you want to nitpick, the half-stops are

    3.4
    4.8
    6.7
    9.5
    13
    19
    etc

    to two significant figures.

    Suppose you want nth stops (ie n=2 for half stops and n=3 for third stops), then the ratio between the stops is 2^(1/(2*n)). Start at an exact f-stop (ie 0.5, 1, 2, 4, 8, 16, 32 etc) not the rounded-off stops (ie 0.71, 1.4, 2.8. 5.6. 11, 22 etc).

    The ratio for half stops is 1.189207 to seven sig figs.

    Best,
    Helen
    PS Who wins the bet?

  6. #6
    Christopher Walrath's Avatar
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    But for a 250mm Soligor telephoto lens, what would be the diameter of the aperture opening at f11? Think ya know?

  7. #7
    Helen B's Avatar
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    No. You've got me there. I don't know how to tell the diameter of the physical aperture opening from only the focal length and the maximum f-stop.

    Best,
    Helen

  8. #8
    Paul Sorensen's Avatar
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    Quote Originally Posted by flash19901
    But for a 250mm Soligor telephoto lens, what would be the diameter of the aperture opening at f11? Think ya know?
    22.7 mm?

  9. #9
    David A. Goldfarb's Avatar
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    Trick question? Didn't Soligor make a 250mm mirror lens, which probably has a fixed aperture?
    flickr--http://www.flickr.com/photos/davidagoldfarb/
    Photography (not as up to date as the flickr site)--http://www.davidagoldfarb.com/photo
    Academic (Slavic and Comparative Literature)--http://www.davidagoldfarb.com

  10. #10
    ann
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    lol lol lol @david.

    and thanks for helen and her math skills. Sometimes half stops are mind bending let along 1/3rds.
    http://www.aclancyphotography.com

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