barrel distortion

Discussion in 'Digital Photography' started by Jimmy Smith, Jun 11, 2004.

  1. Jimmy Smith

    Jimmy Smith Guest

    If you throw a Super Wide Angle lens (ie 14mm) on a digital SLR, are you
    guaranteed to get barrel distortion? If so, at what point focal length does
    it begin and what is the best way to avoid or eliminate it?

    Jimmy
    Jimmy Smith, Jun 11, 2004
    #1
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  2. Jimmy Smith

    Jim Townsend Guest

    Jimmy Smith wrote:

    > If you throw a Super Wide Angle lens (ie 14mm) on a digital SLR, are you
    > guaranteed to get barrel distortion? If so, at what point focal length does
    > it begin and what is the best way to avoid or eliminate it?
    >
    > Jimmy


    If you spend enough on a good rectilinear lens, no, you shouldn't get
    much barrel distortion at all..

    Here are some samples from Canon's EF 14mm f/2.8L USM lens.. Note there is
    little noticeable barrel distortion.

    http://www.pbase.com/cameras/canon/ef_14_28u

    You can pick up the 14mm f/2.8 for around $1800.00 US

    Cheaper lenses will show distortion to varying degrees, and of course
    fisheyes are all about distortion.. Barrel distortion can be corrected
    with software such as Panotools...

    Note that barrel distortion is not limited to ultra wide lenses and can be
    found in longer focal lengths as well.
    Jim Townsend, Jun 11, 2004
    #2
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  3. "Jimmy Smith" <> writes:

    > If you throw a Super Wide Angle lens (ie 14mm) on a digital SLR, are you
    > guaranteed to get barrel distortion? If so, at what point focal length does
    > it begin and what is the best way to avoid or eliminate it?


    No; good rectilinear lenses are actually rectilinear.

    You're likely to get at least *some* on cheaper ones, and especially
    at some settings on cheaper zooms. (Not that "cheaper
    super-wide-angle zooms is a very meaningful phrase!)

    It's quite easy to correct in photo editors. I mostly use Picture
    Window Pro for that kind of thing -- and in fact I don't find anything
    the terms "barrel" and "pincushion" in my photoshop help; but I'm
    several versions out of date due to financial constraints, and I'm
    pretty sure CS now has an easy way to do it.

    It should be corrected *first*, in particular before cropping.
    It's easiest to set up if the center point of the distortion is the
    center of the frame.

    I wonder if there aren't some big wins available by designing lenses
    to exhibit aberrations that are easy to correct electronically, and
    using the extra slack gained there to reduce further the aberrations
    that are *hard* to correct later; or get bigger apertures; or some
    significant gain. Flare, for example, is a real bitch to correct. Or
    field curvature (in an application where you want a flat field,
    anyway).
    --
    David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
    Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    Dragaera/Steven Brust: <http://dragaera.info/>
    David Dyer-Bennet, Jun 11, 2004
    #3
  4. In article <-b.net>, David Dyer-Bennet
    <> writes
    >"Jimmy Smith" <> writes:
    >
    >> If you throw a Super Wide Angle lens (ie 14mm) on a digital SLR, are you
    >> guaranteed to get barrel distortion? If so, at what point focal length does
    >> it begin and what is the best way to avoid or eliminate it?

    >
    >No; good rectilinear lenses are actually rectilinear.
    >
    >You're likely to get at least *some* on cheaper ones, and especially
    >at some settings on cheaper zooms. (Not that "cheaper
    >super-wide-angle zooms is a very meaningful phrase!)
    >
    >It's quite easy to correct in photo editors. I mostly use Picture
    >Window Pro for that kind of thing -- and in fact I don't find anything
    >the terms "barrel" and "pincushion" in my photoshop help; but I'm
    >several versions out of date due to financial constraints, and I'm
    >pretty sure CS now has an easy way to do it.
    >
    >It should be corrected *first*, in particular before cropping.
    >It's easiest to set up if the center point of the distortion is the
    >center of the frame.
    >
    >I wonder if there aren't some big wins available by designing lenses
    >to exhibit aberrations that are easy to correct electronically, and
    >using the extra slack gained there to reduce further the aberrations
    >that are *hard* to correct later; or get bigger apertures; or some
    >significant gain. Flare, for example, is a real bitch to correct. Or
    >field curvature (in an application where you want a flat field,
    >anyway).


    That's a good point. The other aberration which is particularly
    difficult to correct optically (and is not helped at all by stopping
    down) is lateral chromatic aberration (LCA). This is a difference in
    magnification factor for light of different wavelength; separating the 3
    primary colour layers and changing their sizes slightly will remove most
    of the effect.

    As for geometric (barrel/pincushion) distortion, correction may
    sometimes be slightly impaired if the distortion is not entirely first
    order - i.e. not all a simple circle. Sometimes there is a higher order
    component which would require much more sophisticated correction.
    Getting rid of the simple circular component should be good enough in
    most cases though.
    --
    David Littlewood
    David Littlewood, Jun 11, 2004
    #4
  5. David Littlewood <> writes:

    > In article <-b.net>, David Dyer-Bennet
    > <> writes
    >>"Jimmy Smith" <> writes:
    >>
    >>> If you throw a Super Wide Angle lens (ie 14mm) on a digital SLR, are you
    >>> guaranteed to get barrel distortion? If so, at what point focal length does
    >>> it begin and what is the best way to avoid or eliminate it?

    >>
    >>No; good rectilinear lenses are actually rectilinear.
    >>
    >>You're likely to get at least *some* on cheaper ones, and especially
    >>at some settings on cheaper zooms. (Not that "cheaper
    >>super-wide-angle zooms is a very meaningful phrase!)
    >>
    >>It's quite easy to correct in photo editors. I mostly use Picture
    >>Window Pro for that kind of thing -- and in fact I don't find anything
    >>the terms "barrel" and "pincushion" in my photoshop help; but I'm
    >>several versions out of date due to financial constraints, and I'm
    >>pretty sure CS now has an easy way to do it.
    >>
    >>It should be corrected *first*, in particular before cropping.
    >>It's easiest to set up if the center point of the distortion is the
    >>center of the frame.
    >>
    >>I wonder if there aren't some big wins available by designing lenses
    >>to exhibit aberrations that are easy to correct electronically, and
    >>using the extra slack gained there to reduce further the aberrations
    >>that are *hard* to correct later; or get bigger apertures; or some
    >>significant gain. Flare, for example, is a real bitch to correct. Or
    >>field curvature (in an application where you want a flat field,
    >>anyway).

    >
    > That's a good point. The other aberration which is particularly
    > difficult to correct optically (and is not helped at all by stopping
    > down) is lateral chromatic aberration (LCA). This is a difference in
    > magnification factor for light of different wavelength; separating the
    > 3 primary colour layers and changing their sizes slightly will remove
    > most of the effect.


    And in fact Picture Window has a function for correcting that, too.

    > As for geometric (barrel/pincushion) distortion, correction may
    > sometimes be slightly impaired if the distortion is not entirely first
    > order - i.e. not all a simple circle. Sometimes there is a higher
    > order component which would require much more sophisticated
    > correction. Getting rid of the simple circular component should be
    > good enough in most cases though.


    And the correction can be used the other way to simulate a fisheye,
    too.
    --
    David Dyer-Bennet, <mailto:>, <http://www.dd-b.net/dd-b/>
    RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/>
    Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/>
    Dragaera/Steven Brust: <http://dragaera.info/>
    David Dyer-Bennet, Jun 11, 2004
    #5
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