A&P time for a dumb question, what is the aperture number actually a measurement of?

Discussion in 'Lifestyle' started by e.pie, Feb 6, 2008.

  1. e.pie

    e.pie Active Member

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    :dunno:

    and why are the stops at uneven numbers and intervals, ie 2.8, 4, 5.6, 8, etc

    :dunno:
     
  2. e.pie

    e.pie Active Member

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    I'm sure the answer to this is really simple and I'm going to feel retarded :o
     
  3. Gerbonium

    Gerbonium OT Supporter

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    i dont know. i tried looking it up one do but failed
     
  4. Xtreme2k2

    Xtreme2k2 GTI Crew ಠ_ಠ OT Supporter

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    focal length divided by the diameter of the entrance pupil :dunno:

    [​IMG]
     
  5. e.pie

    e.pie Active Member

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    that's not a simple answer :run:
     
  6. Xtreme2k2

    Xtreme2k2 GTI Crew ಠ_ಠ OT Supporter

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  7. wizeguy4

    wizeguy4 New Member

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  8. JordanClarkson

    JordanClarkson OT Supporter

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    it's a measurement of how much light is going to pass through based on the diameter of the opening. it doesn't actually measure light coming through the lens, which is why you are going to have different exposures when taking photos with different lenses despite using the same settings.
     
  9. Jcolman

    Jcolman OT Supporter

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    To further confuse the issue.....while this is a correct statement, for most practical purposes, you can usually use the same f/stop if you switch lenses during the same shoot as long as the light level remains the same.

    If you REALLY want to get all professional and have an absolute correct "f/stop" you will have to find lenses that are calibrated in "T" stops. "T" stands for "transmission", as in light transmission. These lenses are used by cinematographers who often switch lenses in a given scene and have to match the exposure.
     

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