opening angle vertical, horizontal, or diagonal

Discussion in 'Digital Photography' started by bmey, Feb 22, 2007.

  1. bmey

    bmey Guest

    Hello,

    i´m quite new to this topic, so please excuse my possibly stubid
    question. Is an opening angle of 60 degree for a ccd camera meant
    horizontal, vertical or diagonal? The resulting picture isn´t a
    square, so it can´t be all of it.

    yours

    Britta
     
    bmey, Feb 22, 2007
    #1
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  2. bmey

    AustinMN Guest

    I'm not quite sure what an "opening angle" is.

    Austin
     
    AustinMN, Feb 22, 2007
    #2
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  3. bmey

    adminforto Guest

    adminforto, Feb 22, 2007
    #3
  4. bmey

    Roy G Guest

    Hello,

    i´m quite new to this topic, so please excuse my possibly stubid
    question. Is an opening angle of 60 degree for a ccd camera meant
    horizontal, vertical or diagonal? The resulting picture isn´t a
    square, so it can´t be all of it.

    yours

    Britta

    I have been using interchangeable lens cameras since the late 1960s, and I
    have never heard of "Opening Angle".

    The actual angles of view are not much bothered about. Most people just
    rely on what appears in the View Finder.

    I know that a 50mm lens on a 35mm film Camera will give an angle of view
    about 90degrees, and I don't really even need to know that.

    Roy G
     
    Roy G, Feb 23, 2007
    #4
  5. bmey

    bmey Guest


    Hello,

    i´m sorry for the missunderstanding (my english is very bad). The
    correct translation of "Öffnungswinkel" (in german) is aperture angle,
    flare angle. We need to know the mapped area for a known flying
    altitude (scientific purpose). Therefore i need to know in which
    direction the aperture angle is defined.
    Thank you for your answers.

    Britta
     
    bmey, Feb 23, 2007
    #5
  6. bmey

    adminforto Guest

    The angle subtended by the radius of the entrance pupil of an optical
    instrument at the object.
    For photographic camera that should be the diagonal angle of the image plane
    rectangle at the object.



    http://tyrell-innovations-usa.com/shack3d/
     
    adminforto, Feb 23, 2007
    #6
  7. wrote:


    : Hello,

    : i?m sorry for the missunderstanding (my english is very bad). The
    : correct translation of "?ffnungswinkel" (in german) is aperture angle,
    : flare angle. We need to know the mapped area for a known flying
    : altitude (scientific purpose). Therefore i need to know in which
    : direction the aperture angle is defined.
    : Thank you for your answers.

    : Britta

    I believe that the term you are asking about is called in english "angle
    of view" or "field of view". This would be what you would use to
    mathematically calculate the distance imaged along a single axis at a
    specific distance from the camera.

    Unfortunately there is no consistant angle that we can quote you. The
    angle is defined by the "focal length" of the lens (in millimeters) and
    the dimension of the sensor along the particular axis (also in mm). There
    is a nice formula to find the angle you want.

    A=2*arctan(D/(L/2))

    Where A= the angle of view (degrees)
    D= the dimension of the sensor along the appropriate axis (mm)
    L= the lens length (mm)

    So if you wish to figure the angle of view for a 100mm lens along a
    horizontal axis you need to find in your camera's manual the dimensions of
    the sensor (in mm) along the horizontal axis. That becomes D. Then divide
    that by half the lens length (in this case 50). Take the result and take
    the arctangent (on many calculators it is tan-1) and then double the
    result.

    Since each camera will have different sensor dimensions and you will be
    using an unspecified lens, the best I can do is give you the formula and
    let you do the math yourself. :)

    Good Luck

    Randy

    ==========
    Randy Berbaum
    Champaign, IL
     
    Randy Berbaum, Feb 23, 2007
    #7
  8. bmey

    ASAAR Guest

    Dpreview's glossary has a brief description of Picture Angle, with
    a diagram and a few photos. It could have used your formula. :)
    This is the description:
     
    ASAAR, Feb 23, 2007
    #8
  9. bmey

    bmey Guest

    Hello,

    i just found the data i need on the data-sheet of the camera: "Wide
    Field-of-View, 60 degrees with 14 mm, f/2.8 lens". So am i correct to
    think that the focal length of the lense are 28mm (from f/2.8), but
    what is meant by the 14mm? The resolution is: 1920(H)x1080(V), so i
    still don´t know if they mean 60 degrees horizontal, vertical, or
    diagonal. It may well be that i am just a little bit confused now and
    don´t see the solution. Perhaps it would be the best if i ask the
    manufacturer of this camera.

    Thanks for your help.

    Britta
     
    bmey, Feb 23, 2007
    #9
  10. bmey

    ASAAR Guest

    No, the lens's aperture is f/2.8 and that is related to the
    diameter of the lens's large front element. The focal length of
    your camera's lens might be 14mm, but you haven't provided enough
    information about the lens and camera yet. If it's a real 14mm lens
    designed to fit a 35mm film camera or a DSLR, then it's really a
    14mm lens. But if it's being used with a DSLR that doesn't have a
    "Full Frame" sensor, but has a smaller APS-C or 4/3" sensor then
    you'd have to substitute a longer focal length to compensate for the
    smaller sensor size. As an example, if you have a Canon DSLR with
    an APS-C size sensor, the effective focal length would be 22.4mm,
    which is 14mm * Canon's 1.6 "crop factor" or multiplier. If it's a
    Nikon DSLR with a slightly larger APS-C sensor, the effective focal
    length would be 21mm (14mm * 1.5). If it's an Olympus DSLR with a
    4/3" sensor, the effective focal length would be 28mm (14mm * 2).
    This is all assuming that you're not talking about a Point & Shoot
    camera that has a lens with an actual 14mm focal length, which is
    probably a good assumption to make because with most P&S cameras it
    would have the large effective focal length of a telephoto lens.

    So you need to first find out the effective focal length of your
    14mm lens and then use that in the formula with the dimensions of
    your camera's sensor. Your camera's manual should indicate the size
    of the sensor, saying something like APS-C, 4/3", 1/1.8", 1/2.5",
    etc. Dpreview's glossary has a table of dimensions (diameter,
    diagonal, width and height) for a number of different sensor sizes:

    http://www.dpreview.com/learn/?/Glossary/Camera_System/sensor_sizes_01.htm


    Dpreview also has glossary web pages for focal length and focal
    length multiplier:

    http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_01.htm

    http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_Multiplier_01.htm


    The main glossary index page is located at
    http://www.dpreview.com/learn/?/Glossary/
     
    ASAAR, Feb 23, 2007
    #10
  11. The aperture angle determines only the illumination, and has no
    "orientation" connection with orientation in the image plane or the
    image. Also, in complex lenses there may be no actual angle that
    corresponds to the f/#. If you are trying to determine illumination
    at the focal plane, the f/# of the lens is a much better measure than
    trying to determine the acceptance angle from the geometry of focal
    length and aperture diameter.
     
    Don Stauffer in Minnesota, Feb 23, 2007
    #11
  12. bmey

    adminforto Guest

    The angle subtended by the radius of the entrance pupil of an optical
    instrument at the object.
    For photographic camera that should be the diagonal angle of the image plane
    rectangle at the object.



    http://tyrell-innovations-usa.com/shack3d/
     
    adminforto, Feb 23, 2007
    #12
  13. wrote:

    : i just found the data i need on the data-sheet of the camera: "Wide
    : Field-of-View, 60 degrees with 14 mm, f/2.8 lens". So am i correct to
    : think that the focal length of the lense are 28mm (from f/2.8), but
    : what is meant by the 14mm? The resolution is: 1920(H)x1080(V), so i
    : still don?t know if they mean 60 degrees horizontal, vertical, or
    : diagonal. It may well be that i am just a little bit confused now and
    : don?t see the solution. Perhaps it would be the best if i ask the
    : manufacturer of this camera.

    You are definately confusing terms. f/2.8 has nothing to do with the field
    of view. The focal length of the lens is 14mm. The f/2.8 is an indication
    of how well the camera can work in low light conditions but has no effect
    on the amount of the scene able to be seen in the image.

    To help those of us who are trying to understand and help let me define
    what I understand as your intended outcome. You intend to fly in a plane
    over the ground and take photos straight down. You want to use the angle
    and altitude to figure the dimensions on the ground that is imaged. Is
    this right? One problem you still have is that the 60 degrees mentioned in
    your description is likley to be between diagonal corners of the image.
    You need the angle of view for both horizontal and vertical dimensions of
    the image seperately. To find that you need to know the actual dimensions
    of the sensor in the camera. Then using the formula I gave in my last
    post you can calculate the angle horizonally and the angle vertically of
    the view. Just use 14 as the focal length in the calculations. Also be
    sure that when you take the actual images you have your camera set to the
    extreme wide angle end of the zoom so that the camera is actually set at
    14mm or your calculations will not match the image.

    I hope this helps.

    Randy

    ==========
    Randy Berbaum
    Champaign, IL
     
    Randy Berbaum, Feb 24, 2007
    #13
  14. bmey

    J. Clarke Guest

    You are not correct. The focal length of a 14mm lens is 14mm. From
    the f/2.8 you can conclued that the aperture (roughly the diameter) is
    14/2.8=5mm.
    Odds are that the 60mm is diagonal. But you are correct that in the
    absence of actual dimensions (in mm or inches or some other unit of
    distance, not in pixels) of the sensor it is best to contact the
    manufacturer if that information is critical.
     
    J. Clarke, Feb 24, 2007
    #14
  15. Britta,
    sometimes the empiric method is still the better.
    Keep your camera perfectly horizontal over a large sheet of grid paper
    placed on the floor and take a photo of it.

    (this ASCII drawing requires a monospace font, like Courier)

    [O] __
    / \ |
    / \ |
    / \ |
    / \
    / \ H
    / \
    _______/...............\_________ |
    / / \ / |
    / /___________________\ / __|
    / /
    / L /
    /________________________________/

    The proportion between H and L is *always* a constant (similar triangles
    in a Euclidean space - it must be "Ähnlichkeitsregeln" according to
    Wikipedia).
    If you multiply H * altitude, you can obtain the size of L on the ground.

    For a better precision, you can take two photos (keeping the camera
    horizontal and vertical) of 2 signs placed at a know distance between
    them (e.g. 10 meters) from a precise distance (e.g. another 10 meters)
    and measure how many pixels there are between the signs.

    And this works fine without the need to know the exact size of the
    sensor, the precise length of the lens or other strange parameters.

    Of course, if the altitude is *very* high, there is also the Earth
    curvature to be considered.
    I see your University don't have a civil engineering department, but I
    think you can find useful informations about this at the geology department.

    Elementary, my dear Watson...

    Cyrus (the /geometric/ virus - and retired surveyor)
     
    cyrusthevirus, Feb 24, 2007
    #15
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