What is the difference between "Aperture" and "F-Stop"

Discussion in 'Digital Photography' started by Gary Edstrom, May 9, 2005.

  1. Gary Edstrom

    Gary Edstrom Guest

    In looking at the EXIF headers of my pictures, I notice separate entries
    for "Aperture" and F-Stop". Sometimes these entries are the same, and
    sometimes they are different. I have tried looking it up in several
    glossaries, but haven't found anything that really explains the
    difference.

    Thanks, Gary

    --
    Gary Edstrom <>
    Visit my Midway Island home page at http://gbe.dynip.com/Midway
    My reality check bounced!
    The above tagline is number 328 in a series of 547. Collect them all!
     
    Gary Edstrom, May 9, 2005
    #1
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  2. Gary Edstrom

    Jim Townsend Guest

    Gary Edstrom wrote:

    > In looking at the EXIF headers of my pictures, I notice separate entries
    > for "Aperture" and F-Stop". Sometimes these entries are the same, and
    > sometimes they are different. I have tried looking it up in several
    > glossaries, but haven't found anything that really explains the
    > difference.


    F stop and aperture are essentially the same thing.. The aperture is
    measured in stops. The more stops, the smaller the opening.

    Many cameras have duplicate fields in the EXIF info.. For example, my
    Canon 10D has both "Exposure Time" and "Shutter Speed".

    I don't know why they do this :) I'm guessing it's done to maintain
    backwards compatibility with earlier EXIF standards.
     
    Jim Townsend, May 9, 2005
    #2
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  3. Gary Edstrom

    Paul Furman Guest

    Gary Edstrom wrote:

    > In looking at the EXIF headers of my pictures, I notice separate entries
    > for "Aperture" and F-Stop". Sometimes these entries are the same, and
    > sometimes they are different. I have tried looking it up in several
    > glossaries, but haven't found anything that really explains the
    > difference.



    Aperture is the diameter of the opening, f/stop is aperture divided by
    focal length.

    But I think what you are looking at is "maximum aperture of the lens"
    and "f-stop used for this photo".


    --
    Paul Furman
    http://www.edgehill.net/1
    san francisco native plants
     
    Paul Furman, May 9, 2005
    #3
  4. Gary Edstrom

    Backbone Guest

    Aperture and F-Stop are fundamentally the same i.e. the higher the number the
    smaller the lenz diaphragm inside the lens.

    I believe what your seeing is the actual lenz aperture and the aperture setting
    depicted at the cameras end. your camera may have a different reading than your
    lenz may represent. lenz aperture will be the true aperture!

    --
    There are no words that can be heard unless someone listens....
    Remove *flaps* to reply

    "Gary Edstrom" <> wrote in message
    news:...
    > In looking at the EXIF headers of my pictures, I notice separate entries
    > for "Aperture" and F-Stop". Sometimes these entries are the same, and
    > sometimes they are different. I have tried looking it up in several
    > glossaries, but haven't found anything that really explains the
    > difference.
    >
    > Thanks, Gary
    >
    > --
    > Gary Edstrom <>
    > Visit my Midway Island home page at http://gbe.dynip.com/Midway
    > My reality check bounced!
    > The above tagline is number 328 in a series of 547. Collect them all!
     
    Backbone, May 9, 2005
    #4
  5. Gary Edstrom

    peter Guest

    Another way to explain is:
    aperture vs. f-stop is like
    length vs. inches

    "Gary Edstrom" <> wrote in message
    news:...
    > In looking at the EXIF headers of my pictures, I notice separate entries
    > for "Aperture" and F-Stop". Sometimes these entries are the same, and
    > sometimes they are different. I have tried looking it up in several
    > glossaries, but haven't found anything that really explains the
    > difference.
    >
    > Thanks, Gary
    >
    > --
    > Gary Edstrom <>
    > Visit my Midway Island home page at http://gbe.dynip.com/Midway
    > My reality check bounced!
    > The above tagline is number 328 in a series of 547. Collect them all!
     
    peter, May 9, 2005
    #5
  6. Paul Furman <> writes:

    > Gary Edstrom wrote:
    >
    >> In looking at the EXIF headers of my pictures, I notice separate entries
    >> for "Aperture" and F-Stop". Sometimes these entries are the same, and
    >> sometimes they are different. I have tried looking it up in several
    >> glossaries, but haven't found anything that really explains the
    >> difference.

    >
    >
    > Aperture is the diameter of the opening, f/stop is aperture divided by
    > focal length.
    >
    > But I think what you are looking at is "maximum aperture of the lens"
    > and "f-stop used for this photo".


    I'm sure it varies a lot by camera. With my Fuji S2, I get:

    ExposureTime: 1/125
    ShutterSpeed: 1/125
    ShutterSpeedValue: 1/128

    Aperture: 13.0
    ApertureValue: 13.5
    FNumber: 13.0

    (actual values from my photo at
    <http://www.dd-b.net/perl/picpage/dd-b/SnapshotAlbum/data/2005/05070-MCPPA-rally?id=ddb%2020050507%20010-029;IPTC=no;EXIF=raw>).

    I'm interested in the pattern of two the same, one slightly different,
    with the different one having the word "value" in the name. But I
    don't know what, if anything, it means.
    --
    David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
    Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    Dragaera/Steven Brust: <http://dragaera.info/>
     
    David Dyer-Bennet, May 9, 2005
    #6
  7. Gary Edstrom

    Ron Hunter Guest

    Jim Townsend wrote:
    > Gary Edstrom wrote:
    >
    >
    >>In looking at the EXIF headers of my pictures, I notice separate entries
    >>for "Aperture" and F-Stop". Sometimes these entries are the same, and
    >>sometimes they are different. I have tried looking it up in several
    >>glossaries, but haven't found anything that really explains the
    >>difference.

    >
    >
    > F stop and aperture are essentially the same thing.. The aperture is
    > measured in stops. The more stops, the smaller the opening.
    >
    > Many cameras have duplicate fields in the EXIF info.. For example, my
    > Canon 10D has both "Exposure Time" and "Shutter Speed".
    >
    > I don't know why they do this :) I'm guessing it's done to maintain
    > backwards compatibility with earlier EXIF standards.


    Moreover, they aren't always exactly the same, at least on my camera.


    --
    Ron Hunter
     
    Ron Hunter, May 9, 2005
    #7
  8. Gary Edstrom

    Jim Townsend Guest

    Ron Hunter wrote:

    > Jim Townsend wrote:


    >> Many cameras have duplicate fields in the EXIF info.. For example, my
    >> Canon 10D has both "Exposure Time" and "Shutter Speed".
    >>
    >> I don't know why they do this :) I'm guessing it's done to maintain
    >> backwards compatibility with earlier EXIF standards.

    >
    > Moreover, they aren't always exactly the same, at least on my camera.
    >


    Yes, I've noticed that too.. But they are usually very close.

    It seems at least one value is the 'raw' value (with decimal places) and
    the other is nicely rounded.
     
    Jim Townsend, May 9, 2005
    #8
  9. Gary Edstrom

    Gary Edstrom Guest

    Ok, I think I have found the answer to my own question:

    And it involves MATH!

    Take the square root of 2.

    Raise it to the power of the aperature.

    The result is the F-Stop.

    I have tried this on several of my pictures and it works very precicely.

    Example: Aperture=6.9189 F-Stop=11

    (Sqrt(2))^6.9189 = 11.00014

    I have tried it on other pictures and it seems to work.

    On Mon, 09 May 2005 02:59:22 GMT, Gary Edstrom <>
    wrote:

    >In looking at the EXIF headers of my pictures, I notice separate entries
    >for "Aperture" and F-Stop". Sometimes these entries are the same, and
    >sometimes they are different. I have tried looking it up in several
    >glossaries, but haven't found anything that really explains the
    >difference.
    >
    >Thanks, Gary
     
    Gary Edstrom, May 9, 2005
    #9
  10. Gary Edstrom

    Guest

    The problem is that there ate 2 kinds of aperture!

    Linear aperture is the size of the opeinging that the light passes
    throught.
    Relative aperture is F/stop which is focal length divided by linear
    aperture.

    Astronomers use aperture (casually) to mean linear aperture
    Photographers use aperture (causually) to mean F/stop
     
    , May 9, 2005
    #10
  11. Gary Edstrom

    Jack M Guest

    Jack M, May 9, 2005
    #11
  12. Gary Edstrom

    Neil Ellwood Guest

    Gary Edstrom wrote:

    > Ok, I think I have found the answer to my own question:
    >
    > And it involves MATH!
    >
    > Take the square root of 2.
    >
    > Raise it to the power of the aperature.
    >
    > The result is the F-Stop.
    >
    > I have tried this on several of my pictures and it works very
    > precicely.
    >
    > Example: Aperture=6.9189 F-Stop=11
    >
    > (Sqrt(2))^6.9189 = 11.00014
    >
    > I have tried it on other pictures and it seems to work.
    >
    > On Mon, 09 May 2005 02:59:22 GMT, Gary Edstrom
    > <> wrote:

    That is a little more complicated than what I had always understood.

    That the f no. = the number of tomes that the diameter of the aperture
    will divide into the focal length of the lens.
    --
    neil
    delete delete to reply
     
    Neil Ellwood, May 9, 2005
    #12
  13. Gary Edstrom

    Gary Edstrom Guest

    Here is a conversion table to convert from Aperture to F-Stop. This
    seems to match the EXIF data generated by my Canon EOS 20D. Fractional
    apertures would of course fall somewhere between 2 F-Stops. The term
    "Aperture" as used in the EXIF header seems to be a much different
    aperture than we would normally think of. It is a logarithmic scale.
    Each increase of 1 unit on the aperture scale results in a cutting in
    half of the light to the CCD.

    Gary

    Aperture F-Stop

    0 1
    1 1.4
    2 2
    3 2.8
    4 4
    5 5.6
    6 8
    7 11
    8 16
    9 22
    10 32
    11 45
    12 64

    On Mon, 09 May 2005 15:47:41 GMT, Gary Edstrom <>
    wrote:

    >Ok, I think I have found the answer to my own question:
    >
    >And it involves MATH!
    >
    >Take the square root of 2.
    >
    >Raise it to the power of the aperature.
    >
    >The result is the F-Stop.
    >
    >I have tried this on several of my pictures and it works very precicely.
    >
    >Example: Aperture=6.9189 F-Stop=11
    >
    >(Sqrt(2))^6.9189 = 11.00014
    >
    >I have tried it on other pictures and it seems to work.
    >
    >On Mon, 09 May 2005 02:59:22 GMT, Gary Edstrom <>
    >wrote:
    >
    >>In looking at the EXIF headers of my pictures, I notice separate entries
    >>for "Aperture" and F-Stop". Sometimes these entries are the same, and
    >>sometimes they are different. I have tried looking it up in several
    >>glossaries, but haven't found anything that really explains the
    >>difference.
    >>
    >>Thanks, Gary
     
    Gary Edstrom, May 9, 2005
    #13
  14. Gary Edstrom

    Nostrobino Guest

    "Paul Furman" <> wrote in message
    news:...
    > Gary Edstrom wrote:
    >
    >> In looking at the EXIF headers of my pictures, I notice separate entries
    >> for "Aperture" and F-Stop". Sometimes these entries are the same, and
    >> sometimes they are different. I have tried looking it up in several
    >> glossaries, but haven't found anything that really explains the
    >> difference.

    >
    >
    > Aperture is the diameter of the opening, f/stop is aperture divided by
    > focal length.


    Other way around. Focal length divided by size of aperture.

    For example, f/8 says the aperture size is f (the focal length) divided by
    8.

    N.
     
    Nostrobino, May 12, 2005
    #14
  15. Gary Edstrom

    Nostrobino Guest

    "Gary Edstrom" <> wrote in message
    news:...
    > Ok, I think I have found the answer to my own question:
    >
    > And it involves MATH!
    >
    > Take the square root of 2.
    >
    > Raise it to the power of the aperature.
    >
    > The result is the F-Stop.
    >
    > I have tried this on several of my pictures and it works very precicely.
    >
    > Example: Aperture=6.9189 F-Stop=11
    >
    > (Sqrt(2))^6.9189 = 11.00014
    >
    > I have tried it on other pictures and it seems to work.


    I'm not sure what you're doing there, but the standard f-stop series is
    based on multiples of the square root of 2, such that each higher number
    represents half the *area* of the aperture opening and thus passes half as
    much light in the same period of time. (If it were half the *diameter* it
    would have only one-fourth the area and thus pass one-fourth the amount of
    light.)

    Starting with 1, the series is 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 and so on.
    Thus f/2.8 passes half as much light as f/2 but twice as much as f/4, four
    times as much as f/8 and so on. There are in-between stops of course.

    N.
     
    Nostrobino, May 12, 2005
    #15
  16. Gary Edstrom

    Paul Furman Guest

    Nostrobino wrote:
    > "Paul Furman" <> wrote in message
    >>
    >>Aperture is the diameter of the opening, f/stop is aperture divided by
    >>focal length.

    >
    >
    > Other way around. Focal length divided by size of aperture.
    >
    > For example, f/8 says the aperture size is f (the focal length) divided by
    > 8.



    Ah, thanks, that explains the fractional expression of f-stop. Isn't
    that nice when things make sense.


    --
    Paul Furman
    http://www.edgehill.net/1
    san francisco native plants
     
    Paul Furman, May 13, 2005
    #16
  17. Gary Edstrom

    Guest

    In message <>,
    Jim Townsend <> wrote:

    >F stop and aperture are essentially the same thing.. The aperture is
    >measured in stops.


    Not exactly. When aperture is referred to by an f-stop, you have to
    know the focal length to know what the aperture actually is. Aperture
    is measured in millimeters' f-stop is a ratio of focal length to
    aperture.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , May 13, 2005
    #17
  18. Gary Edstrom

    Nostrobino Guest

    "Nostrobino" <> wrote in message
    news:...
    >
    > "Gary Edstrom" <> wrote in message
    > news:...
    >> Ok, I think I have found the answer to my own question:
    >>
    >> And it involves MATH!
    >>
    >> Take the square root of 2.
    >>
    >> Raise it to the power of the aperature.
    >>
    >> The result is the F-Stop.
    >>
    >> I have tried this on several of my pictures and it works very precicely.
    >>
    >> Example: Aperture=6.9189 F-Stop=11
    >>
    >> (Sqrt(2))^6.9189 = 11.00014
    >>
    >> I have tried it on other pictures and it seems to work.

    >
    > I'm not sure what you're doing there, but the standard f-stop series is
    > based on multiples of the square root of 2, such that each higher number
    > represents half the *area* of the aperture opening and thus passes half as
    > much light in the same period of time. (If it were half the *diameter* it
    > would have only one-fourth the area and thus pass one-fourth the amount of
    > light.)
    >
    > Starting with 1, the series is 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 and so
    > on. Thus f/2.8 passes half as much light as f/2 but twice as much as f/4,
    > four times as much as f/8 and so on.


    Oops. That should have read, ". . . four times as much as f/5.6, eight times
    as much as f/8 and so on."

    N.

    There are in-between stops of course.
    >
    > N.
    >
    >
     
    Nostrobino, May 13, 2005
    #18
  19. Gary Edstrom

    Nostrobino Guest

    "Paul Furman" <> wrote in message
    news:...
    > Nostrobino wrote:
    >> "Paul Furman" <> wrote in message
    >>>
    >>>Aperture is the diameter of the opening, f/stop is aperture divided by
    >>>focal length.

    >>
    >>
    >> Other way around. Focal length divided by size of aperture.
    >>
    >> For example, f/8 says the aperture size is f (the focal length) divided
    >> by 8.

    >
    >
    > Ah, thanks, that explains the fractional expression of f-stop. Isn't that
    > nice when things make sense.


    You're welcome, and yes it is. ;-)

    N.
     
    Nostrobino, May 13, 2005
    #19
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