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Thread: 17-40 pincushion distortion

  1. #1
    Armand's Avatar
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    17-40 pincushion distortion

    Hi guys! I have a question: I've heard many things about the 17-40 canon lens - that there are good ones and bad ones and it's sorta luck to get a good one. No matter when and where it's manufactured. Can someone who has this lens please tell me if this is a normal pincushion and barrel distortion for a normal 17-40? The images aren't post-processed in anyway, Canon EOS 5D Mark II is used. Would appreciate it! Thank you.

  2. #2
    Armand's Avatar
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    Re: 17-40 pincushion distortion

    The images are
    17-40 pincushion distortion

    17-40 pincushion distortion
    Last edited by Dave Humphries; 15th May 2012 at 09:20 PM.

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    Re: 17-40 pincushion distortion

    Hello Armand,
    I've owned a Canon 17-40 L lens for nearly six years. I use it on a 5D (the original model). I find it a little difficult to answer your question without knowing the focal length your examples where shot at.
    That said I will try.
    It is completely normal for wide angle zoom lenses (for full frame DSLRs) to have barrel and or pincushion distortion – sometimes both at the same time! The 17-40 L is no exception. In my experience the lens distortion (drawing distortion) can be completely removed in software during RAW file processing. I use DXO to develop my RAW files to DNG files and in the process it automatically removes the lens distortion – and CA and some other stuff too. Adobe and other products will also do this.
    That said I'm not sure that your examples have any particular LENS distortion. Rather, what is shown is so called perspective distortion. In your second image I feel that the lens is likely set at or near 17mm and the camera is not level with the ground. Under those circumstances it is to be expected that verticals not in the centre of the frame will show a marked curvature – like the lamp post at right.
    It may well be that I'm wrong and / or this particular lens is damaged. I have to say that I'm very surprised at the way some lenses get labelled as being good or bad in such extrema ways. Yes, if a lens is damaged it will be bad – no surprise there! Yes, 17-40 L lenses are production items – and as such will exhibit production variations. Frankly, I'd be surprised if an undamaged normal retail sample where found to be “bad”.
    FWIW I love mine. If my gear where stolen and I had the insurance cheque in my hand I'd buy another in a heartbeat.
    HTH.

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    Armand's Avatar
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    Re: 17-40 pincushion distortion

    Hi and thank you for the answer. I think I shot both pictures on 17 mm. I wanted to test the limits. But my biggest concern was the head of the guy in the first picture - the pincushion distortion I think it is. The head is stretched towards the corner quite a bit I think. But maybe this is normal too for this focal length, I have no idea. Any comments on that?

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    DanK's Avatar
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    Re: 17-40 pincushion distortion

    AFAIK, the amount of pincushion and barrel distortion in zoom lenses is a matter of lens design, not often a good copy/ bad copy issue.

    This distortion is easy to fix in many postprocessing software packages. DPP should have a profile for that lens, and I assume lightroom does as well, although I don't have that particular lens, so I have not checked. In LR, fixing this literally only requires checking a box.

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    Administrator Manfred M's Avatar
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    Re: 17-40 pincushion distortion

    This type of distortion is fairly typical of lenses, especially the wider angle ones. Take a look at any of the "pro" lenses any you will find that the zoom factor from shortest to longest focal length is less than 3; and even less at at the super wide angles (my high end zoom goes from 14mm - 24mm). The reason this is done is to limit distortion; primarily the type you are looking at here.

    If it really bothers you; third party software, like DxO can remove the distortion.

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    William W's Avatar
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    Re: 17-40 pincushion distortion

    Quote Originally Posted by Armand View Post
    Hi and thank you for the answer. I think I shot both pictures on 17 mm. I wanted to test the limits. But my biggest concern was the head of the guy in the first picture - the pincushion distortion I think it is. The head is stretched towards the corner quite a bit I think. But maybe this is normal too for this focal length, I have no idea. Any comments on that?
    According to the EXIF the lens was at FL = 17mm
    The affectation of his head is mostly "Keystone Distortion" - and a variation of it because of the cameras postion - see below for the full explanation.

    In common parlance these affectations come under the general non technical heading of “Perspective Distortion” as already mentioned.
    (no criticism is intended for the use of the term “Perspective Distortion” – just pointing out it is not technically correct, but is generally used to cover a range of affections and it’s generally understood what it means)

    ***

    The lens appears to be is actually exhibiting some minor BARREL DISTORTION. (I expect this is normal).

    ***

    Specifically about the Subject's head:

    The Subject’s head being stretched UPWARD is a result of the CAMERA ELEVATION (lower than his eyeballs).

    The Subject’s head being stretched to the T.L.H. corner is the result of CAMERA AXES MIS-ALIGNMENT with the AXES of the SUBJECT (i.e. the camera IS NOT AT RIGHT ANGLES, both vertically and horizontally WITH THE SUBJECT.

    Please see these rough alignment corrections:
    17-40 pincushion distortion


    WW

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    Armand's Avatar
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    Re: 17-40 pincushion distortion

    Very nice, thank you all for the comprehansive answers. From what I understood all this is completely normal and explainable. Thanx!

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    Re: 17-40 pincushion distortion

    A good "rule of thumb" is: "If you're going to use an ultra wide-angle lens around people, keep those people towards the middle of the frame".

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    William W's Avatar
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    Re: 17-40 pincushion distortion

    In the Screen shot above I used Photoshop CS2 V9.0.2 to show the corrections. This is an old version of Photoshop I have on my laptop, the more recent versions have similar and more sophisticated functions.
    Specifically the drop down menu sequence is: “Filter” > “Distort” > “Lens Correction”

    I use the wide angle for portraiture to capture a sense of environment and the Subject’s relation to that environment.
    As Colin mentioned, keeping the main Subject in the middle of the frame is a good first premise as for this somewhat controlled Portrait:

    17-40 pincushion distortion
    Peter-Sesselmann-Artist
    EOS 5D and EF16 to 35F/2.8, Available Light.
    I wanted to give a sense of environment and relationship of the main Subject to HIS environment.

    ***

    This Portrait is not as controlled as the first, but still the same general rule of the Subject in the middle:
    17-40 pincushion distortion
    “My Favourite Barista”
    EOS 5D and EF24L
    F2.8 @ 1/125s @ ISO800 Available Light (Hip Shot).

    Here I wanted to show the superiority and control of the Subject over his (very small) environment.

    ***

    For impact and effect – the Subject is placed at the edge of the frame –
    17-40 pincushion distortion
    “Love those Glasses”
    EOS 5D and 24L, Available Light.

    WW

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    Re: 17-40 pincushion distortion

    Keep in mind that if you're using a 5D, then the full frame has an affect on the distortion. Crop sensors will hit that sweet spot in the middle, so you may see a picture taken on a 7D that the photographer says is completely unedited, but then it will show less distortion, because the camera doesn't pick up that outer area where the distortion shows the most.

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    Re: 17-40 pincushion distortion

    Quote Originally Posted by William W View Post

    For impact and effect – the Subject is placed at the edge of the frame –
    17-40 pincushion distortion
    “Love those Glasses”
    EOS 5D and 24L, Available Light.

    WW
    17-40 pincushion distortion

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    William W's Avatar
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    Re: 17-40 pincushion distortion

    luv yer work!

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    Re: 17-40 pincushion distortion

    Quote Originally Posted by William W View Post
    luv yer work!
    LOL - thanks Bill. They say "never work with children or animals", but I disagree ...

    ... the animals are fine!

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