aperture angle

Discussion in 'Digital Photography' started by logiclips@yahoo.com, May 29, 2005.

  1. Guest

    Hi,

    How can I obtain the aperture angle (in degrees) of a camera when I
    have the aperture (e.g. f/3.2) and the focal length?

    BTW: What is the meaning of this spec?
    Focal Length: 4.5mm (35mm equivalent 37mm)


    Thanks in advance...

    Peter
     
    , May 29, 2005
    #1
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  2. Jim Guest

    <> wrote in message
    news:...
    > Hi,
    >
    > How can I obtain the aperture angle (in degrees) of a camera when I
    > have the aperture (e.g. f/3.2) and the focal length?

    You also need the sensor size, but the aperature is not needed. After that,
    it is a matter of trigonometry.
    >
    > BTW: What is the meaning of this spec?
    > Focal Length: 4.5mm (35mm equivalent 37mm)

    The actual focal length is 4.5mm. The angle of view corresponds to that of
    a 37mm lens on a 35mm image (which is 24x36 mm).
    Jim
     
    Jim, May 29, 2005
    #2
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  3. Jim wrote:
    > <> wrote in message
    > news:...
    >> Hi,
    >>
    >> How can I obtain the aperture angle (in degrees) of a camera when I
    >> have the aperture (e.g. f/3.2) and the focal length?

    > You also need the sensor size, but the aperature is not needed.
    > After that, it is a matter of trigonometry.
    >>
    >> BTW: What is the meaning of this spec?
    >> Focal Length: 4.5mm (35mm equivalent 37mm)

    > The actual focal length is 4.5mm. The angle of view corresponds to
    > that of a 37mm lens on a 35mm image (which is 24x36 mm).
    > Jim


    Except that the sensor is (most likely) 4:3 aspect ratio rather than 3:2
    aspect ratio...

    David
     
    David J Taylor, May 29, 2005
    #3
  4. Guest

    The sensor has a max resolution of 1280 x 960 (1.3 Mio). Is it possible
    to get the sensor size of this information or can I work with 37mm lens
    and 24x36 mm image?
    Furthermore I'm a little bit confused: The aperture angle depends on
    the aperture size, isn't it?

    Thanks,

    Peter
     
    , May 29, 2005
    #4
  5. wrote:
    > The sensor has a max resolution of 1280 x 960 (1.3 Mio). Is it
    > possible to get the sensor size of this information or can I work
    > with 37mm lens and 24x36 mm image?
    > Furthermore I'm a little bit confused: The aperture angle depends on
    > the aperture size, isn't it?


    Sensor sizes are described here:

    http://www.dpreview.com/learn/?/Glossary/Camera_System/Sensor_Sizes_01.htm

    Find out which of these is in your camera.

    I would not use the term "aperture angle", it means nothing to me. You
    can talk about focal length, field of view, and f/number.

    David
     
    David J Taylor, May 29, 2005
    #5
  6. ASAAR Guest

    On 29 May 2005 09:00:27 -0700, wrote:

    > BTW: What is the meaning of this spec?
    > Focal Length: 4.5mm (35mm equivalent 37mm)


    It means that the size of the sensor in the camera with the 4.5mm
    lens is far smaller than the size of the film frame in the 35mm
    camera. If both lenses (37mm and 4.5mm) could be fitted to the same
    35mm camera (assuming that the 4.5mm lens could fill the frame,
    which it probably couldn't), the 4.5mm would resemble a super-wide
    lens. If a picture of an object was taken (at the same distance)
    with both cameras and the film was developed, you could hack at the
    negative produced by the 4.5mm with a pair of scissors. If you cut
    out a rectangular piece of film that shows the same image that is
    contained in the full frame taken by the 37mm lens, that small
    rectangular piece you cut out would be the size of the sensor in the
    camera using the 4.5mm lens. In other words, with that camera, a
    4.5mm lens is equivalent to a 37mm lens in a 35mm camera, because
    uncropped prints from both would show approximately the same image.
     
    ASAAR, May 29, 2005
    #6
  7. wrote:
    > Hi,
    >
    > How can I obtain the aperture angle (in degrees) of a camera when I
    > have the aperture (e.g. f/3.2) and the focal length?
    >
    > BTW: What is the meaning of this spec?
    > Focal Length: 4.5mm (35mm equivalent 37mm)
    >
    >
    > Thanks in advance...
    >
    > Peter


    What is an "aperture angle?" I have never heard the term and I can't
    imagine what it refers to.


    --
    Joseph Meehan

    Dia duit
     
    Joseph Meehan, May 29, 2005
    #7
  8. writes:

    > The sensor has a max resolution of 1280 x 960 (1.3 Mio). Is it
    > possible to get the sensor size of this information [...] ?


    No, this is no use in computing the physical area of the sensor

    But earlier, you wrote:

    >>> Focal Length: 4.5mm (35mm equivalent 37mm)


    This is the data you need to compute sensor size. By dividing 37 by
    4.5, we find a crop factor equal to 8.2 - so the diameter of your
    camera's sensor is 5.3 mm - which means the imager's dimensions is
    something like 4.24 mm x 3.18 mm.

    > Furthermore I'm a little bit confused: The aperture angle depends on
    > the aperture size, isn't it?


    I've never heard the term "aperture angle", so I am not sure what sort
    of formula this would be.

    But if you want to know the angle "seen" by your camera's - that
    particular datum is usually called "field of view" (FOV) and depends
    on focal length and sensor diameter (but not on aperture). You'll
    find the formula explained on this webpage:
    http://folk.uio.no/gisle/photo/crop.html

    For your camera, the FOV a f=4.5mm is atan(5.3/2/4.5), which is
    1.064 radians or ~ 61 degrees. It is the same FOV that a lens
    with f=35mm lens would have with a 24x36 mm imager.
    --
    - gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
    ------------------------------------------------------------------------
    Kodak DCS460, Canon Powershot G5, Olympus 2020Z
    ------------------------------------------------------------------------
     
    Gisle Hannemyr, May 29, 2005
    #8
  9. Neil Ellwood Guest

    wrote:

    >
    > BTW: What is the meaning of this spec?
    > Focal Length: 4.5mm (35mm equivalent 37mm)


    Exactly what it says. The focal length of the lens is 4.5mm which is
    the equivalent to a 35mm camera with a lens of 37mm.
    --
    neil
    delete delete to reply
     
    Neil Ellwood, May 29, 2005
    #9
  10. Neil Ellwood Guest

    Joseph Meehan wrote:

    >
    > What is an "aperture angle?" I have never heard the term and I
    > can't
    > imagine what it refers to.
    >
    >

    Don't tell him but there is no such animal.....
    --
    neil
    delete delete to reply
     
    Neil Ellwood, May 29, 2005
    #10
  11. Guest

    Thanks a lot for these answers.

    With aperture angle I meant the field of view. Sorry for that
    confusion.

    When you compute the FOV with the formula mentioned here
    http://folk.uio.no/gisle/photo/crop.html#fov
    one has to multiply the result with 2, right? Is it because of the 2
    directions from the center of the lense to the edge?
    Is there only one FOV? I thought maybe there are two: for the
    horizontal and vertical direction because of the unsymetric size of the
    sensor? Why not, apparently?

    Peter
     
    , May 29, 2005
    #11
  12. Sheldon Guest

    <> wrote in message
    news:...
    > Thanks a lot for these answers.
    >
    > With aperture angle I meant the field of view. Sorry for that
    > confusion.
    >
    > When you compute the FOV with the formula mentioned here
    > http://folk.uio.no/gisle/photo/crop.html#fov
    > one has to multiply the result with 2, right? Is it because of the 2
    > directions from the center of the lense to the edge?
    > Is there only one FOV? I thought maybe there are two: for the
    > horizontal and vertical direction because of the unsymetric size of the
    > sensor? Why not, apparently?
    >
    > Peter


    I guess my question is why do you need all this FOV info? Just look through
    the viewfinder or at the LCD and that's your field of view. It sounds like
    your camera does not have interchangeable lenses, so what you see is what
    you get. Are you going to get the data on the FOV for a particular focal
    length and then run out and measure how much area your camera will capture?

    Most photogs with any experience will simply use the 35mm equivalent of the
    zoom lens on a point and shoot camera and have a rough idea of what the FOV
    will be (as a mental image, not an exact formula).
     
    Sheldon, May 29, 2005
    #12
  13. Jim Guest

    <> wrote in message
    news:...
    > Thanks a lot for these answers.
    >
    > With aperture angle I meant the field of view. Sorry for that
    > confusion.

    And, just to remind you, the lens aperature has no influence on field of
    view.
    Jim
     
    Jim, May 30, 2005
    #13
  14. ASAAR Guest

    On 29 May 2005 14:36:01 -0700, wrote:

    > Is there only one FOV? I thought maybe there are two: for the
    > horizontal and vertical direction because of the unsymetric size of the
    > sensor? Why not, apparently?


    Most photographers care primarily about one direction when they're
    concerned about FOV, but it could be either one. It's usually
    horizontal for landscapes, sometimes vertical for architectural
    shots. You could have a third FOV. The minimum FOV is the shorter
    of the horizontal or vertical distance, so that's already accounted
    for. The maximum FOV would be based on the diagonal. Find a use
    for it, but don't expect it to bring you fame. :)
     
    ASAAR, May 30, 2005
    #14
  15. writes:
    > Thanks a lot for these answers.
    >
    > When you compute the FOV with the formula mentioned here
    > http://folk.uio.no/gisle/photo/crop.html#fov
    > one has to multiply the result with 2, right?


    Wrong. The formula is:

    FOV = atan(D/2/f)

    where "D" is sensor dimension and "f" is focal length of the lens.

    The normal way to use this formula is to use the diagonal (the
    distance in mm from the lower left corner of sensor to the upper
    right corner of the sensor measured in millimeters) for the letter
    "D". Because the diagonal stretches across the entire sensor,
    the resulting angle is also for the entire sensor, so you don't
    multiply with two.

    > Is it because of the 2 directions from the center of the lense to
    > the edge?


    Again: this has /nothing/ to do with the width of the lens'
    aperture. It is the dimension of the camera's /sensor/ you
    subsitute for "D" in the formula:

    > Is there only one FOV?


    No - there are three: Across (diagonal), width (horizontal) and
    height (vertical)

    > I thought maybe there are two: for the horizontal and vertical
    > direction because of the unsymmetric size of the sensor?


    I computed FOV for the diagonal in my example, because I think that
    is the most interesting datum. It also makes it simple to compare
    the FOV of sensors with different aspect ratios.

    If you want to compute the FOV across the sensor (horizontal
    direction), substitute the /width/ of the sensor for the letter
    "D" in the formula.

    If you want to compute the FOV from top to bottom of the frame
    (vertical direction), substitute the /height/ of the sensor for
    the letter "D" in the formula given above.
    --
    - gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
    ------------------------------------------------------------------------
    Kodak DCS460, Canon Powershot G5, Olympus 2020Z
    ------------------------------------------------------------------------
     
    Gisle Hannemyr, May 30, 2005
    #15
  16. lid writes:
    >On 29 May 2005 14:36:01 -0700, wrote:


    >> Is there only one FOV? I thought maybe there are two: for the
    >> horizontal and vertical direction because of the unsymetric size of the
    >> sensor? Why not, apparently?


    > Most photographers care primarily about one direction when they're
    >concerned about FOV, but it could be either one. It's usually
    >horizontal for landscapes, sometimes vertical for architectural
    >shots. You could have a third FOV. The minimum FOV is the shorter
    >of the horizontal or vertical distance, so that's already accounted
    >for. The maximum FOV would be based on the diagonal. Find a use
    >for it, but don't expect it to bring you fame. :)


    Actually, the diagonal field of view is what interests a lens designer.
    That's the field over which the lens has to deliver a decent quality
    image.

    Dave
     
    Dave Martindale, May 30, 2005
    #16
  17. Stacey Guest

    wrote:

    > Thanks a lot for these answers.
    >
    > With aperture angle I meant the field of view.


    Then do a search for the FOV of a 35mm lens on a 35mm camera and you'll be
    REAL close..

    --

    Stacey
     
    Stacey, May 30, 2005
    #17
  18. ASAAR Guest

    On Mon, 30 May 2005 03:58:04 +0000 (UTC), Dave Martindale wrote:

    > Actually, the diagonal field of view is what interests a lens designer.
    > That's the field over which the lens has to deliver a decent quality
    > image.


    Right, but because of that (lowest quality, usually) it's the
    least desirable part of the image. Poor performance in the corners
    would get a lens and its designers raked over the coals, so it is
    important, but I was trying to think of cases where the average
    photographer would be concerned with getting subjects placed near
    the corners of the frame. Maybe sensors could ease the designer's
    burden by being chamfered, producing an effect like that produced by
    gummed corner mounts that used to hold snapshots in photo albums. :)
     
    ASAAR, May 30, 2005
    #18
  19. Guest

    , May 30, 2005
    #19
  20. writes:
    > IMHO I think one computes FOV/2 with your formula such that tan(FOV/2)
    > = D/2/f.
    > atan(5.3/2/4.5) -> atan(0.589) = 0.532 which is exactly the half of
    > your result.
    >
    > Here are some references which do the same, I think:
    > http://www.cinematography.com/forum2004/lofiversion/index.php?t5207.html
    > http://www.colloquial.com/photo/formats.html
    > http://www.worldserver.com/turk/quicktimevr/calculators.html
    >
    > Or do I have an error or reasoning?


    No - you are right.

    The correct formula is: FOV = 2 x ATAN (D/2/f).

    I do have the correct formula in the spreadsheet I use to compute
    these things - but by error omitted the initial multiply by 2 when
    I copied it from the spreadsheet into the news article.

    Thanks for pointing this out.
    --
    - gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
    ------------------------------------------------------------------------
    Kodak DCS460, Canon Powershot G5, Olympus 2020Z
    ------------------------------------------------------------------------
     
    Gisle Hannemyr, May 31, 2005
    #20
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