Feature: Eliminating Wide-Angle Distortion

Wide-angle lenses are great for packing more into a picture and for capturing images with a slightly unusual perspective. I frequently use wide-angle lenses to take landscape photos, and they also come in handy for pictures of large groups of people. If your digital camera's wide-angle setting isn't particularly wide, you can always buy a screw-on or snap-on wide-angle adapter for your camera. But wide-angle lenses have a downside: They sometimes introduce unwanted distortion into your photo. Of course, the nice part about having a digital camera is that you can easily remove that distortion digitally.

Barrel Distortion

The process behind this unwanted bending is called barrel distortion. A wide-angle lens distorts the image by curving straight lines. You can end up with a picture that doesn't look quite right because the walls of the room are warped like the reflection in a funhouse mirror. Check out the same image with (on the left) and without barrel distortion.

All wide-angle lenses create some amount of barrel distortion, though the effect can vary depending upon the lens. The wider the lens, the more pronounced the effect will usually be. A fisheye lens, in fact, is just a super-wide-angle lens that has the ultimate in barrel distortion. Sometimes you'll want that effect. At other times, you may want to avoid creating funhouse photos.

Minimizing the Distortion

One way to avoid barrel distortion is to simply avoid taking your wide-angle lens all the way to the limit. If it's part of a zoom lens, just back off before you get to the extreme end of the lens' range. If you're using a wide-angle adapter, be careful not to combine too much wide-angle in the camera's built-in zoom with the wide-angle lens attachment. You should be able to see the distortion in the viewfinder if you pay attention, though I know from personal experience that sometimes it creeps in unnoticed until you review the pictures on the computer screen. That's because a little curvature is hard to see in a tiny display, but it's quite apparent on a large 17-inch monitor.

So there's my first bit of advice: To avoid wide-angle distortion, don't shoot in wide-angle mode. I know what you're saying, though--that's a cheap tip, kind of like the old doctor joke that ends in "Don't do that." Fair enough.

You can also disguise barrel distortion. If you're shooting in extreme wide angle, avoid shooting pictures of subjects that have very straight lines you rarely find in nature, like walls, rails, skyscrapers, and other manufactured objects. Most natural scenes, like landscapes, flowers, and animals rebound from barrel distortion much more elegantly.

Splice and Dice

You can avoid using a wide-angle lens entirely by taking several individual pictures with a normal lens and splicing them together afterwards. Consider a shot of the Grand Canyon; you could get the whole thing in a single, massively wide photo, or take three or four separate pictures that would be free of distortion. When you get home, use a panorama stitching program to "glue" the images together into a single photo.

Straighten It Digitally

If you do end up with some photos that have obvious wide-angle distortion, all is not lost. There are several programs available that can help you to reduce or even eliminate curvature in digital photos that were taken with a wide-angle lens. These programs may ask you to vary the lens distortion by some seemingly arbitrary value (a little experimentation and judicious use of the Undo button works wonders) or to simply identify the lines in the photograph, like a wall or horizon, that should be straight. It then "unbends" those lines, hopefully correcting the entire image in the process.

If you received software with your digital camera, check out its collection of filters for an editing tool that will allow you to straighten out your image. Unfortunately, neither PhotoShop nor Paint Shop Pro comes with the necessary tools, but you can install optional add-in filters that will do the job. One effective utility that corrects for barrel distortion can be found in Panorama Tools.

Panorama Tools is free, but it's not the simplest program I've ever tried to use. If you are willing to invest $89, Andromeda Software's LensDoc is a much more user friendly alternative (check out Dave's Favorites for more on LensDoc).

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