One Quick Question...

Discussion in 'Beyond the Basics' started by kalindafarmer, Nov 9, 2005.

  1. kalindafarmer

    kalindafarmer TPF Noob!

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    I was wondering if anyone could tell me EXACTLY what the shutter speed does and what the f-stops do...
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Try a search for 'basic exposure'...you should be able to find some good reading.

    Basically shutter speed it how long the exposure is...and F-stops represent the size of the aperture (hole) through which the light comes into the lens & camera.

    So, if you make the shutter speed longer...you get more light....more exposure. Faster is less exposure.
    If you make the aperture (hole) bigger...you get more light...more exposure. Smaller is less exposure.

    Together the aperture and shutter speed work together to let in a specific amount of light to the film or sensor.
     
  3. KMac

    KMac TPF Noob!

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    Shutter speed is the length of time (usually in seconds) that the shutter is open during the exposure.

    f/number is the focal length of the lens in mm divided by the apeture opening in mm.

    f/stops are special f/numbers that allow exactly 2x and half as much light through the lens as the f/stop above and below it respectively.

    Big numbered f/stops allow a lot of light through the lens to the film so you can use faster shutter speeds (e.g. 1/1000). Small numbered f/stops allow only a little light through so you need slower shutter speeds (e.g. 1/30).

    Big numbered f/stops have a shallow depth of focus.
    Small numbered f/stops have a deep depth of focus.

    I hope this helps,
    Kevin
     
  4. Unimaxium

    Unimaxium TPF Noob!

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    Correction. You have it backwards. Big numbers mean small holes, which mean deep DOF. And small numbers mean large holes, which mean shallow DOF. For example, f1.8 is a very wide opening and creates a very shallow DOF, while f32 is a very small opening but creates a very deep DOF.
     
  5. Hertz van Rental

    Hertz van Rental TPF Noob!

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  6. KMac

    KMac TPF Noob!

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    Doh! Thanks Unimaxium. You are absolutely correct. Must get more sleep. I guess in my mind I think of f/2 etc. as big numbers and f/16 etc as small numbers since they are actually fractions (i.e. 1/2 of the FL or 1/16 of the FL). Differently logic eh?

    Best regards,
    KMac
     
  7. Hertz van Rental

    Hertz van Rental TPF Noob!

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    Wrong again. :lol:
    Not fractions but ratios.
    The f-number is the product of dividing the lens focal length by the diameter of a given aperture.
     
  8. eydryan

    eydryan TPF Noob!

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    i look at this and fail to see how it is a quick question; it's like half the book on photography :lol:
     
  9. KMac

    KMac TPF Noob!

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    Hmm! No. :meh:

    Fractions and ratio are the same thing.

    You get a product when you multiply two numbers. You get a ratio/fraction when you divide two numbers.

    I agree that the f/number is obtained by dividing the focal length by the diameter of an aperture but that doesn't make what I said wrong.

    i.e. the aperture opening represented by f/16 is 1/16th of the focal length. e.g. if you have a 100mm lens and set the aperture to f/16, the aperture opening will be 1/16th of the focal length or 1/16 * 100mm = 6.25mm.

    I think we are both trying to say the same thing. In summary a big number (in the denominator) of the f/number is a small aperture opening. A small number (in the denominator) of the f/number is a big aperture opening.

    Best regards,
    Kevin
     
  10. DocFrankenstein

    DocFrankenstein Clinically Insane?

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    No.

    A fraction is 2 numbers divided by each other. 50/2 and 100/2 are both fractions.

    A ratio is a number... like 2 or 8
     
  11. Hertz van Rental

    Hertz van Rental TPF Noob!

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    And a product is the result you get from any mathematical operation.
    f-numbers are ratios because they stay the same across all lenses.
    f-8 on a 28mm lens will give exactly the same illumination level as f-8 on a 50mm, 100mm, 200, 500mm even though the aperture diameter changes. And they have a ratio sequence with each other as each f-stop is a doubling or halving of illumination level from the previous one.
    The mistake is in seeing f-numbers as f/8 or f/16 (fractions themselves). Although they can be expressed like that to indicate aperture diameter, it has fallen into disuse because it is confusing.
    The true relationship is:
    focal length/aperture diameter = f-number.
    This means that you can have f-numbers with decimal places (eg: 1.2, 1.8, 2.8, 5.6...). You can't have proper fractions with decimals in there.
    We are saying basically the same thing - it's just that you are doing it the hard way ;)
     
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  12. eydryan

    eydryan TPF Noob!

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    fraction :
    1. mathematics number that is not whole number: a number that is not a whole number, e.g. 1/2 simple fraction or 0.5 decimal fraction, formed by dividing one quantity into another

    ratio:
    1. proportional relationship: a proportional relationship between two different numbers or quantities
    [​IMG][​IMG]The ratio of teachers to students at that school is 1 to 27

    2. mathematics one number divided by another: a quotient of two numbers or expressions arrived at by dividing one by the other

    EDIT: product
    4. mathematics result of multiplying: the result of the multiplication of two or more quantities

    so... here are the dictionary definitions now stop fighting about dumb stuff! :hug::

    and yes that is the definition with the illumination :D oh, yeah let's search the dictionary :lol:

    f-number

    camera lens setting: the ratio of the focal length to the effective diameter of a camera lens.
    Symbol f

    [Abbreviation of focal]

    sorry for the big f-number but i copied and pasted it.
     

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