Many specialized photography tools open up new worlds of photographic technique and creative output, but none is more unique and powerful than the perspective control lens. These lenses were designed to mimic the movements of a view camera to bring them to the world of digital SLRs. Also known as tilt-shift lenses, they allow photographers to rotate the front element (the lens plane) so that it’s no longer parallel with the camera’s sensor. The consequences of this are immense: shifting the plane of focus so that it runs diagonally through the scene and making parallel lines appear to converge.
That optical convergence is actually most useful for distortion correction. It’s one of the primary reasons why architectural photographers use perspective control lenses by default. In an interior space, any tilt of the camera will have a huge impact on how straight and true the elements in the scene appear. Tilting the camera up creates visual distortion in parallel lines called keystoning. Its reverse, where tilting down makes lines appear to converge near the bottom of the frame, is called ship’s prow. Turning the camera left or right creates the same effect, distorting horizontal parallels so they appear to converge.
Correcting for this optical distortion is reason enough for photographers who want to keep straight lines straight without sacrificing compositional control to use tilt-shift lenses. With the camera tilted up, the lens is adjusted so that its optics are tilted down, minimizing that keystoning. It’s evidenced in the interior image shown here. Notice how straight and true the lines are? There are limits to these movements, of course, but when compared to an unaltered image the correction is significant.
Aside from this distortion correction, however, perspective control lenses can be used for expanded focus control as well. A photographer who wants to increase depth of field when photographing a still life, for instance, can achieve it by tilting the lens forward. This rotates the plane of focus so that instead of running vertically through the scene it’s practically laid down nearer to parallel with the tabletop. (If you’d like to dig into this in more detail, read up on the Scheimpflug principle. It’s a bit dry but definitely fascinating if you’re into optical physics.)
With the lens tilted down and the plane of focus nearing perpendicular to the sensor plane, it makes it easier to keep objects in focus from front to back within the frame. Think about it. With the plane of focus parallel to the sensor, a smaller aperture has limitations on its front-to-back sharpness capability. But when the optics rotate to send the plane of focus outward from the lens, upping the aperture makes it easier to make elements in focus all the way from foreground to background.
Conquering such technical challenges as depth of field and distortion make tilt-shift lenses worth the investment for those who need them. But for the rest of us, it’s the creative control the lenses provide that makes them particularly fun to experiment with.
For instance, to create an incredibly narrow depth of field, that same tilt or swing lens movement combined with a wide aperture makes the plane of focus a thin swath of sharpness that runs diagonally through the frame. How bizarre! It’s a great way to isolate a single point of focus in an otherwise cluttered frame by throwing most of it out of focus. The only downside is sometimes a random background element is in focus along with the center of interest.
Perspective control lenses are also incredibly useful for the fun technique of making a wide-angle landscape or cityscape appear to be in miniature. Using the same tilt or swing technique, a streetscape photographed from above with a wide aperture will appear to have a razor-thin depth of field. That kind of shallow focus isn’t typically available in wide-angle views. Because it’s typically a function of smaller scenes, it makes the shot appear to be of a world in miniature.
Though that miniature effect can be faked, it never looks quite as good as the real thing; there’s no digital substitute for the effectiveness of these modifications made in-camera with actual optics. If experimenting with a perspective control lens sounds like fun, consider renting one for just a few bucks a day from a local camera shop or online rental service such as lensrentals.com or borrowlenses.com. Options abound from wide to telephoto from makers including Rokinon, Canon and Nikon. And for those who want to really experiment with fun and funky focus effects, consider a uniquely malleable optic such as the Lensbaby Composer Pro II (pictured above).