Tilt–shift photography refers to the use of camera movements on small- and medium-format cameras, and sometimes specifically refers to the use of tilt for selective focus, often for simulating a miniature scene. Sometimes the term is used when the shallow depth of field is simulated with digital post-processing; the name may derive from the tilt–shift lens normally required when the effect is produced optically. “Tilt–shift” encompasses two different types of movements: rotation of the lens plane relative to the image plane, called tilt, and movement of the lens parallel to the image plane, called shift.
Tilt is used to control the orientation of the plane of focus (PoF), and hence the part of an image that appears sharp; it makes use of the Scheimpflug principle. Shift is used to adjust the position of the subject in the image area without moving the camera back; this is often helpful in avoiding the convergence of parallel lines, as when photographing tall buildings. Movements have been available on view cameras since the early days of photography; they have been available on smaller-format cameras since the early 1960s, usually by means of special lenses or adapters.
Nikon introduced a lens providing shift movements for their 35 mm SLR cameras in 1962, and Canon introduced a lens that provided both tilt and shift movements in 1973; many other manufacturers soon followed suit. Canon currently offers four lenses that provide both movements while Nikon offers three. Such lenses are frequently used in architectural photography to control perspective, and in landscape photography to get an entire scene sharp. Some photographers have popularized the use of tilt for selective focus in applications such as portrait photography.
The selective focus that can be achieved by tilting the plane of focus is often compelling because the effect is different from that to which many viewers have become accustomed. Walter Iooss Jr. of Sports Illustrated, Vincent Laforet, Ben Thomas, and many other photographers have images using this technique on their web sites. A camera lens can provide sharp focus on only a single plane. Without tilt, the image plane (containing the film or image sensor), the lens plane, and the plane of focus are parallel, and are perpendicular to the lens axis; objects in sharp focus are all at the same distance from the camera.
When the lens plane is tilted relative to the image plane, the plane of focus (PoF) is at an angle to the image plane, and objects at different distances from the camera can all be sharply focused if they lie in the same plane. With the lens tilted, the image plane, lens plane, and PoF intersect at a common line; this behavior has become known as the Scheimpflug principle. When focus is adjusted with a tilted lens, the PoF rotates about an axis at the intersection of the lens’s front focal plane and a plane through the center of the lens parallel to the image plane; the tilt determines the distance from the axis of rotation to the center of the lens, and the focus determines the angle of the PoF with the image plane. In combination, the tilt and focus determine the position of the PoF.
In applications such as landscape photography, getting everything sharp is often the objective; by using tilt, both the foreground and background can often be made sharp without the use of a large f-number. When the PoF coincides with an essentially flat subject, the entire subject is in focus; for a subject that is not flat, obtaining foreground and background sharpness relies on the depth of field, though the sharpness can often be obtained with a smaller f-number than would be needed without the use of tilt. Basically, this shifts the whole plane of focus keeping one of the 3 axes as it is.
The PoF can also be oriented so that only a small part of it passes through the subject, producing a very shallow region of sharpness, and the effect is quite different from that obtained simply by using a large aperture with a regular camera. Using tilt changes the shape of the depth of field (DoF). When the lens and image planes are parallel, the DoF extends between parallel planes on either side of the PoF. With tilt or swing, the DoF is wedge shaped, with the apex of the wedge near the camera, as shown in Figure 5 in the Scheimpflug principle article. The DoF is zero at the apex, remains shallow at the edge of the lens’s field of view, and increases with distance from the camera.
For a given position of the PoF, the angle between the planes that define the near and far limits of DoF (i.e., the angular DoF) increases with lens f-number; for a given f-number and angle of the PoF, the angular DoF decreases with increasing tilt. When it is desired to have an entire scene sharp, as in landscape photography, the best results are often achieved with a relatively small amount of tilt. When the objective is selective focus, a large amount of tilt can be used to give a very small angular DoF; however, the tilt fixes the position of the PoF rotation axis, so if tilt is used to control the DoF, it may not be possible to also have the PoF pass through all desired points.
View camera users usually distinguish between rotating the lens about a horizontal axis (tilt), and rotation about a vertical axis (swing); small- and medium-format camera users often refer to either rotation as “tilt”. In a subject plane parallel to the image plane, parallel lines in the subject remain parallel in the image. If the image plane is not parallel to the subject, as when pointing a camera up to photograph a tall building, parallel lines converge, and the result sometimes appears unnatural, such as a building that appears to be leaning backwards.
Shift is a displacement of the lens parallel to the image plane that allows adjusting the position of the subject in the image area without moving the camera back; in effect the camera can be aimed with the shift movement. Shift can be used to keep the image plane (and thus focus) parallel to the subject; it can be used to photograph a tall building while keeping the sides of the building parallel.
The lens can also be shifted in the opposite direction and the camera tilted up to accentuate the convergence for artistic effect. Shifting a lens allows different portions of the image circle to be cast onto the image plane, similar to cropping an area along the edge of an image.
Again, view camera users usually distinguish between vertical movements (rise and fall) and lateral movements (shift or cross), while small- and medium-format users often refer to both types of movements as “shift”. Whereas the image circle of a standard lens usually just covers the image frame, a lens that provides tilt or shift must allow for displacement of the lens axis from the center of the image frame, and consequently requires a larger image circle than a standard lens of the same focal length.