Dealing with wide-angle distortion

Wide-angle lenses, with their rounded glass, frequently create an effect known as barrel distortion, where what otherwise would be straight lines in your image become bent and the overall image takes on the shape of a barrel. This phenomenon is more noticeable where there are straight lines in the scene you are shooting (such as a city with lots of walls, streets, and so forth), and less noticeable where lines are abstract (such as water, sky, or landscapes). When shooting a portrait of a group of people, a wide-angle lens may distort the shapes of people’s faces and bodies, especially if they are on the edge of the frame.

Image 6-14 is an unedited photo, taken in an Algiers marketplace with an EF 15mm f/2.8 Fisheye lens, and it shows some of the positive and negative elements of a wide-angle shot. On the positive side, emphasizing the amount of nuts for sale gives a dramatic look to the image. More challenging, however, is the range of exposure, from the dark upper-left corner where the merchant is on the phone, to the nuts in the foreground, which are slightly overexposed, to the upper-right corner that is overexposed beyond repair. Additionally, the bystander on the far right is obviously distorted due to being on the edge of the fisheye image.

Acceptable or not? The exposure can be adjusted a little, and perhaps the barrel distortion could be helped with an image-editing application, but parts of the image would have to be cropped. Taken with a 1D Mark II using an EF 15mm f/2.8 Fisheye lens, ISO 400, 1/320 second at f/7.

Sometimes you can use this effect to your advantage, such as to emphasize a foreground element, which makes it more noticeable and interesting in your subject (such as the cobblestones are in the Hermitage image in 6-13). Or, you may want to turn a wide-angle shot into a panoramic image by cropping out the upper and lower parts of a landscape-framed shot.

Often there is a straight line that extends across the center of your image that you can occasionally use to your advantage, such as if you are shooting a road or there is a distinct horizon. In 6-15, I was shooting the 2005 world championships in Leipzig, Germany, and the wide-angle distortion provided a dramatic effect. I was able to use the fencing strip as a point-of-reference for a straight horizontal line. However, I tilted the camera slightly too much, and consequently the strip looks a bit too curved and the photo looks unnatural.

The center line of this image is actually the top of the spectators' heads. While not too off, I wanted to make the straight line (the fencing strip) a more obvious part of the subject Taken with a 1D Mark II using a 15mm Fisheye lens, ISO 1250, 1/125 second at f/2.8.

There are some image-editing applications that easily let you adjust barrel distortion. ACDSee Pro, for example, has a lens-correction feature to let you adjust distortion; the only downside to using this is that when you adjust the image using the software, elements of the edges of the photo are cropped out (see 6-16). There are also plug-ins for Photoshop, such as PhotoFixLens from HumanSoftware (www.HumanSoftware.com) and Fisheye-Hemi from Image Trends (www.ImageTrendsInc.com), that let you adjust barrel distortion.

Using ACDSee Pro's iens-correction feature, I can adjust the distortion in the wide-angle photo shown in 6-15 so that the straight line is corrected to what I want.

Category: Science of Lenses

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