Common photography myths (6)

Myth #5: Wide-angle lenses distort the image

September 5th, 2009 - 08:34:30 PM:

That misconception may be rooted in the fact that there's only a single word in the English language for different kinds of distortion. It's better to say “lens distortion” when we talk about distortions caused by the lens design, and “perspective distortion” when talking about distortions caused by perspective. Since there are different ways to design a wide angle lens, there are different degrees of lens distortions resulting from the design. You can find designs that intentionally don't even try to correct distortions. These are called “fish-eye lenses”, delivering not only very wide angles of view of about 180 degrees, but also extreme distortions. Straight lines of the original scene are rendered as strongly bent curves in the image.

On the other end of the spectrum you'll find the more expensive wide-angle primes that display virtually no distortions (it's harder to reduce distortions with zooms, so you can expect considerably stronger distortions even from expensive wide-angle zooms). These render straight lines of the scene as straight lines in the image. These lenses prove that wide-angle lenses do not generally distort the image.

So what happens when you stand in front of a skyscraper and take a photo of it with a wide-angle lens? The image looks strongly distorted at first sight. Well, it is, but it's not lens distortion, but perspective distortion. When the straight edge of the skyscraper is a straight edge in the image, the lens causes little to no distortions. What you see is distortions caused by perspective, i. e. by the fact that the base of the skyscaper is much closer to you than the tip, so the base appears much bigger. A tele-photo lens would give you the same distortions of you used it from the same position. You only don't do this usually, because you want to fit the entire skyscraper into the frame.

The only way to reduce perspective distortion is to change perspective. Changing the lens doesn't help. If you photograph the skyscraper from a distance then all parts of the building are at about the same distance from you, and you won't see much of perspective distortions. You will probably use a telephoto lens in this situation, so again it looks like avoiding the wide-angle lens reduces distortions. However, this is coincidence, not cause.