Monday, January 11, 2010

A Small Word on Radial Distortion

I got an email last week that I'd like to address:

I own the Nikon 18-200mm lens, and I'm wondering why my photos don't look the way I want them to. When I take photos of my kids with this lens in particular it makes their faces look fat. I spent a lot of money on my camera and lenses and don't understand what I'm doing wrong. What can I do??

From,
Confused mother with fat-faced kids


Don't worry confused mother, I'm here to help. I get a lot of people who have just bought a Rebel or D90 and want to know which lens they should buy to make their pictures look better. My first suggestion is to use the one you have until you want something more, and then you'll know what lens to buy. There are a few lenses that I would recommend staying away from. Stay away from seemingly "all in one" lenses such as the 18-200mm lens, or the 55-200mm zoom lens. These lenses seem to give you lots for the money because the range is so wide. However, these lenses carry a hefty price on your photos: radial distortion.
There are two kinds of radial distortion in photographic lenses: barrel and pincushion.
barrel distortion in camera lenses
Barrel distortion is commonly seen in wide-angle zoom lenses

pincushion distortion in camera lensesPincushion distortion is more commonly seen in low-end telephoto lenses.

And while distortion of some kind is almost inevitable in any zoom lens, it is much more prevalent in low-end zoom lenses.

The 18-200mm lenses also have what is called mustache distortion, which is a combination of the two. With mustache distortion, You will see barrel distortion towards the middle of your image, and pincushion distortion towards the edges. Bad. Bad. Bad. Image distortion is apparent when you're taking pictures of buildings, or of a window (something that is straight) and you see the building edges start to curve. The effect of barrel distortion is exaggerated with fisheye lenses, which can be a good thing when you want to capture an infinitely wide area on a finite image plane.
barrel distortion from a fisheye lens
Barrel distortion from a fisheye lens can be a good thing, if you're getting it when you want it.


However, for the most part, barrel and pincushion distortion will mess you up. OK, maybe not you, but at least your image. Take a look of these examples:


Pincushion distortion "pushes in" the center of the images, giving us an image that is not true-to-life.


Barrel distortion "pushes out" from the center of the image, making things look really gross.

So how do you get help for such nastiness? Is there a cure for this plague of bad imagery? Of course. Start by shooting with prime lenses. Prime lenses are fixed lenses that tend to have much wider apertures and have less distortion. Sometimes giving the benefit of 4 full stops lower (as in the case of my 50mm F/1.2L vs. the 18-55mm F/3.5-5.6 IS EF-S lens). Every camera company offers prime lenses, and some photographers I know only shoot with prime (and tilt-shift) lenses. It really depends on what you're shooting. I do recommend having at least one prime lens. They're not expensive, in fact, Canon and Nikon both offer 50mm prime lenses for less than a C-note.

Canon's 50mm F/1.8 EF prime lens

Nikon's 50mm F/1.8D prime lens

After you've played with the 50mm, try going the other way and purchasing a fisheye lens, to help you understand how barrel distortion can enhance your pictures, when used properly. Fisheye lenses are quite a bit more, starting at around $600.

Another cheap way to reduce distortion is to stay away from "all in one" lenses, they are the red-headed stepchild of photography. This is because their radial distortion effects (and mustache distortion) don't benefit the photo at all, in fact, they make it look worse. If you like zoom lenses, try to get lenses with a narrower focal range, such as the 18-55 F/2.8 EF-S lens, or the 70-200 F/4L lens (only $500, street price). The key to distortion in photography is to only let it creep in when you want it. It can create some amazing imagery, some of my favorite photos were taken with a fisheye lens, but that's because I choose to let distortion rule the field, which can only happen after you understand the uses of it.

Feel free to email me your photography questions: clane {at} clanegessel {dot} com