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Thread: Lens Distortion Correction - Help

  1. #1

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    Lens Distortion Correction - Help

    Hi All,

    Below is a picture, with what I suspect to be some sort of lens distortion lurking in the background. The main area where this can be seen (if you haven't spotted it already) is on the building to the left of the picture.I have a number of questions related to this horrible perspective shift:

    1) What is this type of distortion called
    2) what causes it
    3) how can I avoid it
    4) how can I correct it

    Lens Distortion Correction - Help

    Thanks in advance for your time,
    Rob

  2. #2
    Moderator Donald's Avatar
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    Re: Lens Distortion Correction - Help

    Rob

    The answers to the specific questions you pose are not the primary reason for this tutorial. But if you go to it, I think you'll find that you will learn what some of the issues in your image are about.

  3. #3

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    Re: Lens Distortion Correction - Help

    Quote Originally Posted by EDGE1 View Post
    Hi All,

    Below is a picture, with what I suspect to be some sort of lens distortion lurking in the background. The main area where this can be seen (if you haven't spotted it already) is on the building to the left of the picture.I have a number of questions related to this horrible perspective shift:

    1) What is this type of distortion called
    2) what causes it
    3) how can I avoid it
    4) how can I correct it

    Lens Distortion Correction - Help

    Thanks in advance for your time,
    Rob
    This is caused due to camera positioning low and pointing upwards

    Lens Distortion Correction - Help
    Last edited by Ashwin; 23rd November 2011 at 08:34 PM.

  4. #4

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    Re: Lens Distortion Correction - Help

    Quote Originally Posted by EDGE1 View Post
    Hi All,

    Below is a picture, with what I suspect to be some sort of lens distortion ...........
    And the lens you used (or setting if zoom) was ...??
    As mentioned above, it seems to be perspective issue rather than lens distortion.
    Lens distortion comes as barrelling or pin cushioning, neither of which seem to be the case here.
    Great sky BTW.
    Graham

  5. #5
    Moderator Donald's Avatar
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    Re: Lens Distortion Correction - Help

    Quote Originally Posted by GrahamH View Post
    And the lens you used (or setting if zoom) was ...??
    Graham

    The Exif data shows us that it was the EF-S15-85mm f/3.5-5.6 IS USM at 16mm.

    And that is the issue, as identified by Ashwin. When you get into the realms of the very or ultra, wide-angle then the management of perspective becomes crucial.

  6. #6
    Mark von Kanel's Avatar
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    Re: Lens Distortion Correction - Help

    eeerrrrm wide lens, good depth of field with the perspective that is expanded with converging verticals in the back
    ground, is that the problem? if so and im talking out of my bottom here...

    put the image into 2 layers in PS, correct the background for perspective and re merge????

    yes/no?

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    Re: Lens Distortion Correction - Help

    Quote Originally Posted by EDGE1 View Post
    how can I avoid it
    Hi Rob,

    The short answer is "you need to keep the camera sensor perfectly vertical" - unfortunately - unless you're using a tilt/shift lens, that then may mean that you can't compose the shot correctly (unless you can stand on a ladder for this kind of shot).

    Often the best work-around is to shoot much wider than you need, and then adjust in Photoshop (because correcting for perspective distortion can throw away a significant part of the image).

  8. #8

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    Re: Lens Distortion Correction - Help

    Hi all,

    A combination of the answers given here, and the tutorial from Donald has helped a great deal in understanding this problem.

    I tried to correct the distortion using "lens correction" in CS5, but I lost loads of the picture. Instead I used Free Transform --> Transform --> Warp.

    Seems to have worked....

    Lens Distortion Correction - Help

    Thanks,
    Rob

  9. #9
    Moderator Donald's Avatar
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    Re: Lens Distortion Correction - Help

    Rob

    Very glad you've managed to both understand the problem and find the answer to it, with some help from CiC'ers.

    Now take one with you standing above the subject and point the camera downwards ... and look at the effect.

    Particularly when you're operating with a very wide angle lens (or a zoom at the very wide angle end), the issue of perspective distortion becomes major feature of your planning process for the shot. Colin has indicated what the answer is. On some occasions you may in fact want to induce perspective distortion for artistic effect. But it's much better to be doing it deliberately and consciously than it being the result of an accident that you don't understand.

  10. #10
    Moderator Dave Humphries's Avatar
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    Re: Lens Distortion Correction - Help

    Quote Originally Posted by EDGE1 View Post
    ~ I used Free Transform --> Transform --> Warp.

    Seems to have worked....

    Lens Distortion Correction - Help
    Hi Rob,

    When the camera is obviously pointing up, it is usually wise to slightly under correct, as you'll notice Ashwin has.

    I think you got away with it here (in fact it is slightly under corrected on the right) - often; if a 'looking up' image is completely corrected (and everything is parallel), it can look like it has been overdone and things are diverging at the top, which looks really false.

    Cheers,

  11. #11

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    Re: Lens Distortion Correction - Help

    Quote Originally Posted by Dave Humphries View Post
    Hi Rob,

    When the camera is obviously pointing up, it is usually wise to slightly under correct, as you'll notice Ashwin has.
    Aha, I see. Excellent tip, thanks.

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