Tilt-Shift Photography

Tilt-shift photography refers to the use of camera movements on small- and medium-format cameras; it usually requires the use of special lenses.
“Tilt-shift” actually encompasses two different types of movements: rotation of the lens 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 change the line of sight while avoiding the convergence of parallel lines, as when photographing tall buildings.
Another, less cost-intensive technique called “tilt-shift miniature faking” is a process in which a photograph of a life-sized location or object is manipulated so that it looks like a photograph of a miniature-scale model

Tilt-shift miniature faking


A common technique for making an image of a full-size scene resemble an image of a miniature model is to have the image progressively blurred from the center to the top or bottom, simulating the blurring due to the limited DoF of a typical image of a miniature. The blurring can be accomplished either optically or with digital postprocessing.

Techniques

Optical

Miniatures can be simulated optically by using lens tilt, although the effect is somewhat different from the shallow DoF that normally results in close-up photography.
In a normal photograph, i.e., one not using tilt,

• The DoF extends between two parallel planes on either side of the plane of focus; the DoF is finite in depth but infinite in height and width.
• The sharpness gradients on each side of the DoF are along the line of sight.
• Objects at the same distance from the camera are rendered equally sharp.
• Objects at significantly different distances from the camera are rendered with unequal sharpness.

In a photograph using tilt,

• The DoF extends between two planes on either side of the plane of focus that intersect at a point beneath the lens .
• The DoF is wedge shaped, with the apex of the wedge near the camera, and the height of the wedge increasing with distance from the camera^.
• When the plane of focus is at a substantial angle to the image plane, the DoF can be small in height but infinite in width and depth.
• The sharpness gradients are at an angle to the line of sight. When the plane of focus is almost perpendicular to the image plane, the sharpness gradients are almost perpendicular to the line of sight.
• When the plane of focus is at a substantial angle to the image plane, objects at the same distance from the camera are rendered with unequal sharpness, depending on their positions in the scene.
• Objects at greatly different distances from the camera are rendered sharp if they are within the DoF wedge.

Despite the differences, for a scene that includes relatively little height, lens tilt can produce a result similar to that of a miniature scene, especially if the image is taken from above at a moderate angle to the ground. For a completely flat surface, the effect using tilt would be almost the same as that with a regular lens: the region of focus would be sharp, with progressive blurring toward the top or bottom of the image. The image of Jodhpur was made from such a scene; although the blurring was accomplished with digital postprocessing, a similar result could have been obtained using tilt.
Miniature faking using tilt is less effective if a scene includes objects of significant height, such as tall buildings or trees, especially when photographed at a small angle to the ground, because there is a sharpness gradient along surfaces that are obviously the same distance from the photo camera.
Though probably less common, similar difficulties arise if an object has significant extent along the line of sight, such as a long train receding from view, again photographed at a small angle to the ground, because parts of the train that are obviously at considerably different distances from the camera are rendered equally sharp.
With a view camera, tilt can usually be set with movements built in to the photo camera; with a small- or medium-format camera, a tilt-shift lens or adapter is usually required.

Tilt-Shift photo gallery 

information from wikipedia.org and smashingmagazine.com