X zoom equals 35 mm

Discussion in 'Digital Photography' started by m Ransley, Feb 28, 2006.

  1. m Ransley

    m Ransley Guest

    What is the formula for converting the optical x zoom stated that equals
    the 35mm figures I am used to. Whay didn`t they just keep 35mm lens
    numbers instead of going to "equals x zoom" The old way I know. To know
    what X zoom it achieves in 35mm don`t you have to base it on the
    lenses widest setting. So 3x for one camera will not be as long as 3x
    for another camera with a wider lens? 35mm numbers are simpler.
     
    m Ransley, Feb 28, 2006
    #1
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  2. m Ransley

    Bill Funk Guest

    Those focal lengths on the lens are the focal lengths for those
    lenses.
    For a compact digital camera, the focal lengths are as listed; the
    reason they have a conversion listed is because most people won't be
    able to relate the real FL range of, say, 8mm to 24mm to anything in
    35mm film terms without having the equivalents listed. Thus, the FL
    would be listed as something like, "35mm ~ 105mm equivalent", which is
    the same 3x zoom range as the actual 8mm ~24mm zoom focal length
    range.
    Even DSLRs that aren't "full frame" have a crop factor given, so when
    actual 35mm lenses are used, the user knows what the effective focal
    lengths are, in 35mm equivalents.

    As for exactly what that factor is, it depends on the size of the
    sensor used in the camera model in question. One very easy way to
    determine the equivalent FL is to look the camerta up on a review site
    (like Dpreview); the equivalents are usually given there.
     
    Bill Funk, Feb 28, 2006
    #2
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  3. There is none. They refer to completely different, unrelated, aspects
    of the lens.

    A camera that advertises a "10x zoom lens" means that the maximum
    focal length is 10 times the minimum focal length. A 36mm to 360mm
    zoom lens is a 10x zoom, and so is an 18mm to 180mm zoom lens.
     
    David Dyer-Bennet, Feb 28, 2006
    #3
  4. m Ransley

    rafe b Guest


    "X zoom" simply refers to the ratio of the longest
    focal length the the shortest.

    To calculate the 35 mm "equivalents" you'd have to
    know the actual min and max focal lengths, and the
    sensor size.

    For a 5x7 mm sensor (for example,) the diagonal is
    8.6 mm, so 8.6 mm would be "normal" -- ie., the
    equivalent of 50 mm on a 35mm camera.

    For that sensor, a zoom range of, say, 4.3 mm to
    12.9 mm (a "3x zoom") would be the equivalent of
    25 mm to 75 mm, referenced to 35 mm cameras.

    [Note: I've lied a bit; technically, the normal
    length on 35 mm cameras 43 mm -- based on the
    diagonal -- but 50 mm is an "accepted" value
    and makes for simpler math above.]


    rafe b
    www.terrapinphoto.com
     
    rafe b, Feb 28, 2006
    #4
  5. 3X is a better marketing tool than 35 - 105, especially in the low to
    mid line camera market. There is no formula to convert them since a 3X
    zoom could be 3mm to 9 mm or a 200mm - 600 mm or any of thousands of others.
     
    Joseph Meehan, Feb 28, 2006
    #5
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