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Olympus 12-40 Pro Lens distortion at 12mm? See pic

Discussion in 'Native Lenses' started by dlhomesolutions, Apr 4, 2016.

  1. dlhomesolutions

    dlhomesolutions Mu-43 Regular

    172
    Sep 30, 2013
    Peoria, IL
    Hi. I took a few shots at the wide focal length that seem to appear a little distorted or even fisheye like towards the ends. Do you gave the same issue? Here is an example Sam and Josie-1-2.
     
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  2. WhidbeyLVR

    WhidbeyLVR Mu-43 Top Veteran

    606
    Feb 14, 2014
    Whidbey Island
    Lyle
    The 12-40 has significant barrel distortion on the wide end. When it is digitally corrected, the corners of the frame get stretched out to a wide rectilinear projection. This gives you the stretched effect you see. I have found that in cases like this, it is often preferable to leave the barrel distortion uncorrected. Then you will get something more like this:

    Sam and Josie-1-2z.
     
    Last edited: Apr 5, 2016
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  3. dlhomesolutions

    dlhomesolutions Mu-43 Regular

    172
    Sep 30, 2013
    Peoria, IL
    Ok yeah, that is much better. How do I undo the barrel distortion?
     
  4. WhidbeyLVR

    WhidbeyLVR Mu-43 Top Veteran

    606
    Feb 14, 2014
    Whidbey Island
    Lyle
    That depends on your tools and workflow. If you are working from raw, disable any geometric correction in your raw converter (I don't know what camera or raw converter you are using).

    If you just have the JPEG, then you could try what I did to create the demo above. I dragged your image into Hugin and set the lens "b" distortion parameter to 0.05 to "recreate" the barrel distortion.

    Hugin is surprisingly useful for all sorts of things you might not expect!
     
  5. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    I don't think what we're seeing here is barrel distortion though there may be a small amount of barrel distortion present. I think what we're seeing is a combination of 2 other things.

    The first is a perspective based distortion that becomes more noticeable with wide angle lenses which tend to produce a "broadening" of things towards the side of the frame, part of the perspective that goes with a much wider field of view than your eye normally encompasses. The shorter the focal length, the more noticeable this effect becomes. The best solution is to increase your distance from your subjects and allow a little space between the outside subject on each side and the side of the frame. You can notice that the effect is much worse in the outer subject on each side. Increase the distance, leave space at the sides, and it will be much less noticeable, and you can crop the photo slightly if you don't want the dead space at the sides in the final image. Your processing software may include some lens correction options so that you don't need to go to another application like Hugin. In Lightroom, for example, you can go to the Lens Corrections panel, select the Manual tab, and play with the Aspect slider to fix that issue.

    There's a second problem in your photo, however, that is contributing to the degree of distortion apparent and that is keystoning. Your camera was pointed slightly down rather than level so the subjects bodies also lean out slightly towards the edge of the frame at the top compared to the bottom of the frame, the way the sides of a building converge towards the top when you point the camera up. That, coupled with the broadening towards the sides, is what creates the "fisheye" effect. You can also adjust for keystoning in the Manual lens corrections in Lightroom but doing so makes the top of the frame a little narrower than the bottom of the frame and you have to crop. The problem with this image is that the outer subjects are so close to the edges of the frame that cropping to avoid the angled side edges of the frame ends up cropping part of each of the outer subjects. If you use Photoshop and you can successfully do a fill in the missing area on each side, you may avoid the need for cropping.

    So, my recommendations are as follows:

    1- to avoid the need for corrections, shoot from a little further away in order to allow some free space in the frame on either side of your group and keep the camera pointed horizontally. You will need to shoot from below eye height to avoid having lots of dead space above your subjects heads so you will need to hold the camera lower and look down at the screen or alternatively use a tripod or squat a little if you are going to use the viewfinder. You may want to crop the resulting images slightly.

    2- If you need to do corrections, correcting for the perspective effects at the edge of the frame is much less of a problem than correcting for keystoning, not because the process is any more difficult (both simply amount to moving a slider) but because correcting for keystoning results in angled sides at the side of the frame which do need to be cropped and if the subjects are too close to the side of the frame you may end up cropping a bit of the person on each side of the group.

    So, for different reasons, leaving a bit of space to the side of people towards the edge of the frame is always a good idea when you're shooting with a wide angle lens because the perspective effects tend to look distorted the closer you get to the side of the frame, and the keystoning you get if the lens is pointed slightly up or down can help to make that even more noticeable as it has here.
     
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  6. WhidbeyLVR

    WhidbeyLVR Mu-43 Top Veteran

    606
    Feb 14, 2014
    Whidbey Island
    Lyle
    I was not suggesting that the OP's image showed barrel distortion. His image showed the stretched corners which are typical of a correct wide-angle rectilinear projection. What I said was, that in this case the image may be more pleasing with the barrel distortion of the lens uncorrected (or reintroduced through digital processing).

    Correcting the perspective (keystone) on a wide-angle rectilinear image will still leave a noticeable stretching distortion on the edges of the frame (as well as leaving one to either over-crop the edges or fill the corners, as you noted). Notice how broad the faces are on the bridesmaids at the edges and the black upper corners of this perspective (keystone) corrected image:
    Sam and Josie-1-2x.

    Another option to improve the image in post-processing is to perform the perspective correction and then reproject the image using some sort of cylindrical projection. Here is an example with perspective corrected and image rendered using Hugin's "Panini General" projection. The empty upper corners are still a problem, but nobody has a fat face:
    Sam and Josie-1-2y.

    I agree with all your suggestions for avoiding these issues at the picture-taking stage.
     
    Last edited: Apr 5, 2016
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  7. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    Just for comparison with Lyle's corrected image above, here's the full frame from Lightroom with an Aspect correction to correct for the broadening of the 2 outer subjects and a Vertical correction to correct for the keystoning. It will be immediately obvious why I recommend increasing your shooting distance slightly and leaving some empty space to the sides of the frame.

    Sam and Josie-1-2.

    The girl on the right is a little closer to the edge of the frame than the girl on the left so the broadening distortion is a little more obvious in her case. I think I could probably increase the Aspect correction a little more for her but doing so is going to make the end result of correcting for the keystoning even worse by increasing the angling in the 2 upper corners. With a bit more distance and a bit of space on each side it would be relatively simple to correct for both distortions and crop the sides without cropping into either of the 2 outer girls. I think correcting for the keystoning as well as the other distortion makes for a nicer result but you may not agree.
     
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  8. Klorenzo

    Klorenzo Mu-43 All-Pro

    Mar 10, 2014
    Lorenzo
    I agree with previous comments. What program are you using? Are you using RAW or JPEG?

    Most programs (Lightroom, DxO, etc.) automatically correct for geometrical distortions for the specific lens and focal length you are using. With other (Darktable) you have to activate the correction by hand. If you shoot JPEG the corrections are already performed by the camera.

    So if you know that the lens specific corrections have already been applied you may consider other kind of corrections.

    I did two quick attempts in Hugin, cilindrical projection, then quickly cloned out the wall to fill the missing corners. I prefer the first one even if is less corrected.

     
  9. dlhomesolutions

    dlhomesolutions Mu-43 Regular

    172
    Sep 30, 2013
    Peoria, IL
    I am using Lightroom. I think the pic the first responder posted looks great. I am working in raw but I had to post the .jpg in the site because it would not allow me to upload raw files. (A major oversight for a photo forum)
     
  10. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    A RAW file is not an image file, it is the data required for creating an image. If you could post a RAW file, it would not display as an image in your message. Readers would need to download it and process it in RAW conversion software in order to view the photograph, and it would open in that RAW conversions software with no processing at all having been applied apart from whatever default processing the software applies to provide a starting point for the user's own edits. People following this forum who shoot JPEG and who do not possess any RAW conversion software would be completely unable to view it. Finally, RAW files tend to be many times larger in size than JPEG image files and the forum's servers would need considerably greater storage capacity to hold the files and the increased server load imposed by readers downloading the files to view in their own conversion software would impact on server performance and make loading of threads and JPEG images less responsive.

    It is not an oversight for a forum such as this to refuse to allow the upload of RAW files, it is actually an extremely sensible decision which ensures everyone can view all of the images posted and helps maintain the performance standards of the forum.
     
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