Distortion Correction With Any Lens

When an architectural photographer is hired to photograph a structure, chances are he’s going to use some specialized equipment. Namely, he’s going to employ a tilt/shift (or perspective control) lens in order to minimize the distortion that occurs when a camera is tilted up to photograph a building. Any time the film plane (or sensor plane) isn’t parallel with the planes in the structure, distortion will appear to make parallel lines converge. It’s called keystoning when the camera is pointed up at a building and the structure takes on a more triangular shape than the rectangle that it should be. An architectural lens—the tilt-shift or perspective control lens—can compensate for this optical distortion and keep those lines parallel.

The problem is tilt-shift lenses are quite expensive and not the kind of thing most photographers carry on a regular basis. So what do you do when you’re traveling, for instance, and you come across a building you’d like to photograph? Or what if you simply need to use a wider lens than the tilt-shift you have in your kit? In each case, the solution is to compose correctly to minimize distortion in the camera and then correct what distortion does appear with some fairly simple post-processing techniques.  

Compose Correctly

How you aim your lens has a huge impact on distortion. When you tilt the camera up, the vertical lines in a building’s structure are no longer parallel to the camera sensor. This divergence causes distortion—and the greater that tilt, the more pronounced the distortion.

So instead of aiming the camera up at the structure, use a wide enough lens such that you can compose while keeping the camera level and the sensor plane parallel to the façade of the structure. This will mean you’re composing with the building near the top of the frame. You’ll have a lot of unwanted foreground in the photo, but this can be easily cropped out. And if you have to tilt up just a little bit, you’ll get just a little bit of distortion. That small bit of keystoning can be more easily repaired using the next technique once you’ve downloaded the images onto the computer.

Fine-Tune In Post

Failing the ability to keep vertical lines parallel during composition—or to fine-tune minor distortion that occurs in conjunction with the above technique—using Lightroom’s Transform tool is a great way to correct keystoning distortion.

In the Transform heading of the Develop module, first try the Auto setting to see if Lightroom can approximate the correct perspective to straighten the lines in the image. Then try the Vertical transformation section. Adjusting the Vertical slider will amplify distortion or correct for the keystoning that occurs when aiming a camera up at a building. The horizontal slider corrects for similar distortion that occurs when the camera is turned left or right to diverge from parallel to the façade. The Rotate slider helps correct horizon lines, while Aspect helps stretch the image horizontally or vertically. Scale is useful for enlarging the image to hide any canvas edges that may appear from any of the above corrections, and X and Y offset sliders shift the center of the frame left, right, up and down. The useful grid guides that appear when making vertical and horizontal slider adjustments ensure you can align lines in the composition with true horizontal and vertical reference lines.

With this simple set of Transformation controls, almost any distortion correction that occurs when photographing architecture can be dramatically improved.

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