Focal length in pixels

Discussion in 'Computer Support' started by orelza@gmail.com, Apr 11, 2007.

  1. Guest

    Hey any body out there who can help me transform focal length in mm to
    focal length in pixels. to be precise am trying to get 24mm to pixels
    for scanned areal photos with dimensions 4992 x 3328 pixels. and for
    153mm with dimensions 7242 x 7263 pixels.

    Thanks.
    , Apr 11, 2007
    #1
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  2. Desk Rabbit Guest

    wrote:
    > Hey any body out there who can help me transform focal length in mm to
    > focal length in pixels. to be precise am trying to get 24mm to pixels
    > for scanned areal photos with dimensions 4992 x 3328 pixels. and for
    > 153mm with dimensions 7242 x 7263 pixels.
    >
    > Thanks.
    >

    I know SFA about the subject but a Google search of the term "focal
    length in pixels" turned up millions of hits.

    Results 1 - 10 of about 1,410,000 for focal length in pixels. (0.09 seconds)

    What couldn't you find? Couldn't anybody in any of the photography or
    affiliated groups help?
    Desk Rabbit, Apr 11, 2007
    #2
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  3. On Wed, 11 Apr 2007 09:53:01 -0700, orelza wrote:

    > Hey any body out there who can help me transform focal length in mm to
    > focal length in pixels. to be precise am trying to get 24mm to pixels
    > for scanned areal photos with dimensions 4992 x 3328 pixels. and for
    > 153mm with dimensions 7242 x 7263 pixels.
    >
    > Thanks.


    Lionel?


    --
    #1 Offishul Ruiner of Usenet, March 2007
    #1 Usenet Asshole, March 2007
    #1 Bartlo Pset, March 13-24 2007
    #10 Most hated Usenetizen of all time
    Pierre Salinger Memorial Hook, Line & Sinker, June 2004
    COOSN-266-06-25794
    Google Tech Support, Apr 11, 2007
    #3
  4. Lionel Guest

    On Wed, 11 Apr 2007 13:39:31 -0400, Google Tech Support
    <> wrote:

    >On Wed, 11 Apr 2007 09:53:01 -0700, orelza wrote:
    >
    >> Hey any body out there who can help me transform focal length in mm to
    >> focal length in pixels. to be precise am trying to get 24mm to pixels
    >> for scanned areal photos with dimensions 4992 x 3328 pixels. and for
    >> 153mm with dimensions 7242 x 7263 pixels.
    >>
    >> Thanks.

    >
    >Lionel?


    There's no such thing as "focal length in pixels", so the question
    doesn't have an answer. 'Focal length' on a camera lens relates to the
    distance between the front of the lens & the plane where the image is
    projected:
    <http://en.wikipedia.org/wiki/Focal_length>

    If the OP explains in more detail what s/he is trying to actually
    achieve, I might be able to come up with a more helpful answer.

    --
    W "Some people are alive only because it is illegal to kill them."
    . | ,. w ,
    \|/ \|/ Perna condita delenda est
    ---^----^---------------------------------------------------------------
    Lionel, Apr 11, 2007
    #4
  5. Lionel wrote:
    > On Wed, 11 Apr 2007 13:39:31 -0400, Google Tech Support
    > <> wrote:
    >
    >> On Wed, 11 Apr 2007 09:53:01 -0700, orelza wrote:
    >>
    >>> Hey any body out there who can help me transform focal length in mm to
    >>> focal length in pixels. to be precise am trying to get 24mm to pixels
    >>> for scanned areal photos with dimensions 4992 x 3328 pixels. and for
    >>> 153mm with dimensions 7242 x 7263 pixels.
    >>>
    >>> Thanks.

    >> Lionel?

    >
    > There's no such thing as "focal length in pixels", so the question
    > doesn't have an answer. 'Focal length' on a camera lens relates to the
    > distance between the front of the lens & the plane where the image is
    > projected:
    > <http://en.wikipedia.org/wiki/Focal_length>
    >
    > If the OP explains in more detail what s/he is trying to actually
    > achieve, I might be able to come up with a more helpful answer.
    >

    STFU kiwi fagg0t
    Text Medium No. 5, Apr 11, 2007
    #5
  6. Whiskers Guest

    On 2007-04-11, <> wrote:
    > Hey any body out there who can help me transform focal length in mm to
    > focal length in pixels. to be precise am trying to get 24mm to pixels
    > for scanned areal photos with dimensions 4992 x 3328 pixels. and for
    > 153mm with dimensions 7242 x 7263 pixels.
    >
    > Thanks.


    What are you actually trying to do?

    In so far as the question has any meaning at all (one might as well ask for
    a focal length in ounces or gallons), perhaps this is the answer, from
    <http://www.worldserver.com/turk/quicktimevr/calculators.html>:

    Field of View from EXIF Data

    In the images captured by some digital cameras, there is some data that
    is useful to determine the field of view for stitching panoramas.

    Ideally, this would be the focal length in pixels, but unfortunately
    the focal length is given in millimeters. In order to determine the
    field of view, it is necessary to know the density of pixels (in
    pixels per millimeter) on the virtual imaging sensor associated with
    the image. Again, this pixel density is usually given in pixels/inch,
    so conversion to pixels/mm is needed as well. The pixel density may be
    different for the horizontal and vertical directions.

    From the focal length in pixels, and the number of pixels in each
    dimension of the image, it is possible to compute the field of view in
    each dimension.

    To convert from focal length in mm to focal length in pixels, where
    pixel density is given in pixels/inch, use:

    focalPixels = focalMM * pixelDensity / 25.4

    To compute the field of view from focal length in pixels, use:

    fov = 2 * atan( (H - 1) / (2 * focalPixels) )

    where H is either width or height, for the field of view in the
    respective direction. These equations are encapsulated into the
    calculator below.

    (there is a 'calculator' there apparently designed to perform the
    calculations described). I won't try to comment on what that page is
    trying to do or how it does it.

    --
    -- ^^^^^^^^^^
    -- Whiskers
    -- ~~~~~~~~~~
    Whiskers, Apr 11, 2007
    #6
  7. WhzzKdd Guest

    "Whiskers" <> wrote in message
    news:...
    > On 2007-04-11, <> wrote:
    >> Hey any body out there who can help me transform focal length in mm to
    >> focal length in pixels. to be precise am trying to get 24mm to pixels
    >> for scanned areal photos with dimensions 4992 x 3328 pixels. and for
    >> 153mm with dimensions 7242 x 7263 pixels.
    >>
    >> Thanks.

    >
    > What are you actually trying to do?
    >
    > In so far as the question has any meaning at all (one might as well ask
    > for
    > a focal length in ounces or gallons), perhaps this is the answer, from
    > <http://www.worldserver.com/turk/quicktimevr/calculators.html>:
    >
    > Field of View from EXIF Data
    >
    > In the images captured by some digital cameras, there is some data that
    > is useful to determine the field of view for stitching panoramas.
    >
    > Ideally, this would be the focal length in pixels, but unfortunately
    > the focal length is given in millimeters. In order to determine the
    > field of view, it is necessary to know the density of pixels (in
    > pixels per millimeter) on the virtual imaging sensor associated with
    > the image. Again, this pixel density is usually given in pixels/inch,
    > so conversion to pixels/mm is needed as well. The pixel density may be
    > different for the horizontal and vertical directions.
    >
    > From the focal length in pixels, and the number of pixels in each
    > dimension of the image, it is possible to compute the field of view in
    > each dimension.
    >
    > To convert from focal length in mm to focal length in pixels, where
    > pixel density is given in pixels/inch, use:
    >
    > focalPixels = focalMM * pixelDensity / 25.4
    >
    > To compute the field of view from focal length in pixels, use:
    >
    > fov = 2 * atan( (H - 1) / (2 * focalPixels) )
    >
    > where H is either width or height, for the field of view in the
    > respective direction. These equations are encapsulated into the
    > calculator below.
    >
    > (there is a 'calculator' there apparently designed to perform the
    > calculations described). I won't try to comment on what that page is
    > trying to do or how it does it.
    >

    Dang - atan = ancient history! I totally forgot everything they ever tried
    to teach me in trig class!
    WhzzKdd, Apr 11, 2007
    #7
  8. Whiskers Guest

    On 2007-04-11, WhzzKdd <frack_this@email_is.invalid> wrote:
    > "Whiskers" <> wrote in message
    > news:...
    >> On 2007-04-11, <> wrote:


    snip

    > Dang - atan = ancient history! I totally forgot everything they ever tried
    > to teach me in trig class!


    You can get the same result by drawing the triangles to scale and
    measuring the angles with a protractor, if you can draw accurately enough.

    --
    -- ^^^^^^^^^^
    -- Whiskers
    -- ~~~~~~~~~~
    Whiskers, Apr 11, 2007
    #8
  9. WhzzKdd Guest

    "Whiskers" <> wrote in message
    news:...
    > On 2007-04-11, WhzzKdd <frack_this@email_is.invalid> wrote:
    >> "Whiskers" <> wrote in message
    >> news:...
    >>> On 2007-04-11, <> wrote:

    >
    > snip
    >
    >> Dang - atan = ancient history! I totally forgot everything they ever
    >> tried
    >> to teach me in trig class!

    >
    > You can get the same result by drawing the triangles to scale and
    > measuring the angles with a protractor, if you can draw accurately enough.
    >


    My thoughts exactly <g>! And NOTHING I'd build would require any more
    accuracy than that.
    WhzzKdd, Apr 11, 2007
    #9
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