Photographing the House, Street and Town

By Sandy Sorlien

This begins a series of practical and philosophical articles on the photography of architecture and urbanism.

Correcting the Keystone Effect

I know you own a camera. And if you love architecture and urbanism as much as I do, you are using it to photograph buildings -- perhaps when you travel to European villages or Asian temples or Mexican ruins; perhaps when you visit American cities; perhaps when you tour a new TND. If you're an architect or planner, you're probably using it to document your own work and the work of colleagues, to share images on a website or listserv, illustrate a promotional brochure or monograph, or deliver a PowerPoint or slide lecture.

The photography of buildings is an especially difficult undertaking, in large part because perspective must be managed carefully in order for the building or streetscape to look natural. The most common type of perspective distortion in most photographs of buildings is called "keystoning." The building comes out shaped like a keystone -- well, an upside-down keystone, actually -- wide at the bottom and narrow at the top. This is what happens when the camera back is tilted upward relative to the vertical axis of the building, as it must be if the building is much taller than you are. The effect is particularly egregious when you're using a wide-angle lens. And because new urbanist buildings in particular are often situated on narrow streets, you must use a wide-angle lens to get the whole building in the frame.

Professional photographers of architecture solve this and other perspective problems by using cameras or lenses where the lens plane and film plane can be moved independently of each other. If you have a large-format view camera with "movements" or, on your smaller-format camera, a special "shift" or perspective-control (PC) lens, you can avoid keystoning by keeping the film plane (camera back) parallel to the building. When you do this the top of the building is usually cut off, but if you simply apply some "rise" to the lens plane, the image circle shifts upward and the top of the building comes back into view.

Such equipment can be alarmingly expensive, or, at least,cumbersome and difficult to operate. I'll present here some strategies for correcting keystoning using your existing point-and-shoot or basic 35mm camera, digital or film-based. Try one or more of these techniques:

• Stand on something. I have a 26-inch aluminum stepladder with a blue plastic top, made by Werner. It cost $34 from my neighborhood hardware store, Stanley's. (No, you may not buy this at Home Depot, you sprawlmonger you.) I call this excellent little ladder my "shift lens" because it enables me to get some rise simply by standing on it. It's lightweight and I carry it around with one hand, or leave it in the car trunk until I really need it. True, you look like an idiot up there taking a picture, but it's a great conversation-starter. (Security guard at the Philadelphia Naval Base: "May I ask WHAT the hell you're doing up on that ladder?") If you don't have a ladder or stool, look for a low wall, high curb, front stoop, grassy knoll, crusty snow bank, or the shoulders of a large companion, standing opposite the building you want to shoot.

• Get back farther from the building. The farther away you are, the less keystoning there will be because you won't have to tilt the camera upward as much.

• Get MUCH farther back and use a longer lens.

• Include more foreground. Remember, keystoning will be reduced if you can keep the camera back closer to parallel to the vertical axis of the building. Instead of tilting the camera up to center the building in your scene, place the building higher in the frame so you don't have to tilt as much. You can crop any excess foreground later.

• Correct distortion digitally. In Photoshop, under the View menu, choose Show Grid. Then under Select, choose All. Then under Edit, choose Transform and then Perspective. You can then pull the arrow cursor in at the lower right corner to square the building to the grid. Caution: the shape of the building will change somewhat as you correct keystoning. A small correction is no problem, but a massive correction will produce an elongated building height. Here, the first two photographs show a house in Kentlands shot with a digital camera. The first image is keystoned slightly because I had to tilt the camera up to get the top of the building in the frame. The second image was corrected in Photoshop. Other image editing programs have similar perspective control. It's simple to use.

• Don't overcorrect. Often, a little keystoning is desirable. Our goal is to produce a photograph of a house that looks natural, that looks something like the way we'd experience it if we were standing there. Tall buildings (say, three or more stories) shot from close in, or houses perched up on a hill, can look strange if the edges are perfectly parallel to the frame. Visually and psychologically, in the real world we experience some diminished perspective in such cases and expect it. In fact, if there is perfect parallelism we sometimes think the top of the building is looming, which looks wrong and even a little frightening. Many professionals, after leveling the camera and applying rise to get the top of the building in the image circle, then deliberately tilt their film plane slightly to introduce a bit of keystoning.

A building that looks natural in a photograph doesn't call attention to the photographer's technique or lack of it. Managing the keystone effect is half the battle in allowing the building to be itself.

Sandy Sorlien is a photographer and writer living in Philadelphia. She serves on the National Board of Directors of the Society for Photographic Education, and is the author of "Fifty Houses: Images from the American Road."