Trade Tricks: Getting It Straight
Correcting distortion of architecture in the computer
Photographers know that wide-angle lenses sometimes cause distortion. Straight lines appear curved, especially if they're close to the edges of the frame. Sometimes, the effect is desirable, and other times, it's not.
Distortion actually can occur with any lens. One of the most common examples is photographing architecture. Standing at the base of a tall building with the camera pointed upward, the lines of the building, which are actually parallel, appear to converge in the viewfinder. This perspective distortion, called "keystoning," is only remedied by keeping the film plane parallel to the subject plane, but that often means you won't get the whole building in the shot. Architectural photographers frequently use large-format view cameras because their specialized movements allow the photographer to correct problems like keystoning while they shoot.
Those optical corrections are helpful, but they're impossible to achieve without the right equipment. That means point-and-shoot cameras, 35mm SLRs and even high-end medium-format cameras aren't readily able to deliver these corrections.
That's where computer software can help. Armed with any camera and almost any photo-editing program, photographers can correct architectural distortion in the computer. All you need to do is stretch and pull your pictures until those lines are parallel.