Tilt-shift Photography

Selective focus
Selective focus can be used to direct the viewer's attention to a small part of the image while de-emphasizing other parts.
With tilt, the effect is different from that obtained by using a large f-number without tilt. With a regular camera, the PoF and the DoF are perpendicular to the line of sight; with tilt, the PoF can be almost parallel to the line of sight, and the DoF can be very narrow but extend to infinity. Thus parts of a scene at greatly different distances from the camera can be rendered sharp, and selective focus can be given to different parts of a scene at the same distance from the camera.
With tilt, the depth of field is wedge shaped. As noted above under Tilt, using a large amount of tilt and a small f-number gives a small angular DoF. This can be useful if the objective is to provide selective focus to different objects at essentially the same distance from the camera. But in many cases, effective use of tilt for selective focus requires a careful choice of what is sharp as well as what is unsharp, as Vincent Laforet has noted. Because the tilt also affects the position of the PoF, it may not be possible to use a large amount of tilt and have the PoF pass through all desired points. This may not be a problem if only one point is to be sharp; for example, if it is desired to emphasize one building in a row of buildings, the tilt and f-number can be used to control the width of the sharp area, and the focus used to determine which building is sharp. But if it is desired to have two or more points sharp (for example, two people at different distances from the camera), the PoF must include both points, and it usually is not possible to achieve this while also using the tilt to control DoF.