Field-Of-View: Proportional To Lens Length?

Discussion in 'Photography' started by (PeteCresswell), Jul 26, 2012.

  1. I've got an IP cam here: http://xcam.zapto.org:8080/image/cam3
    (that's just a single still frame...)

    The purpose is to allow windsurfers to see if other sailors are
    planing or not.

    Right now, it's kind if iffey.... needs tb zoomed some more.

    Current cam supports zooming and is zoomed to 9mm. I'm shopping
    for another cam: one with fewer features, but replaceable lens.

    I would like to restrict the frame to the area between the hotel
    on the left and the green flag in the middle of the frame.

    Eyeballing it, that seems like a 50% reduction in field.

    Does that mean that going from a 9mm lens to a 18mm lens would do
    the job? Or is it non-linear?
     
    (PeteCresswell), Jul 26, 2012
    #1
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  2. (PeteCresswell)

    Alan Browne Guest

    Yes (with a little ish).

    More proper to say the magnification is proportional to FL.

    A 100mm has 2x the magnification of a 50mm lens. Or half the field of view.

    Proportions won't be exact due to distortion. But that's negligible in
    most cases.

    And since many lenses don't match their 'label' FL perfectly, there will
    be a small difference. For example some "50"mm lenses are actually 48mm.
     
    Alan Browne, Jul 26, 2012
    #2
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  3. It's linear. It's also linear to the sensor size (here: width).

    Double the width of the sensor, you need double the lens length
    for the identical view.

    Example:
    Your old, 9mm camera has a sensor 6mm wide.
    Your new camera has a sensor 8mm wide.
    You need
    18mm * 8mm/6mm = 24mm
    a 24mm lens.

    -Wolfgang
     
    Wolfgang Weisselberg, Jul 31, 2012
    #3
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