Tilt-Shift photography is the technique of using selective focus. This is used to reduce the magnitude of large size photos to make it into miniature models. One moves the lens adjacent to the plane of the image in the shift phase while moving the lens through an angle to that of the image plane is termed as tilt.
During the tilt step, a large aperture is used so as to obtain a shallow depth of the field under focus. The ultimate aim is to tilt the lens so that only a small portion of the larger perspective is under focus. In some cases the lens might be rotated in an axis parallel to that of the film. In this case it is termed as the shift as mentioned above.
With the help of a view camera it is easy to achieve tilt and shift. Most view cameras enable you to adjust the lens and camera to increase or decrease the point of focus. A tilt shift lens which is also known as the perspective control lens is often used with a medium format camera which might have as much freedom as a view camera. Further in a medium or a small format camera even with the help of a perspective control lens you may not be able to achieve a lot of range.
A short focus Perspective control lens is used in architecture planning, while longer focus lenses are used in landscape modeling and close up shots. The Perspective control lens has an image circle that is unarguably larger than most other lenses enabling it to cover the entire image area. The film is usually large and lens movements are restricted. This ensures that one cannot shift the image area to outside of the image circle.
There are several Perspective control lens including the ones by Nikon and PC Nikkor both of which were used in SLR lenses. SLR cameras are very good for tilt-shift photography. The SLR lens gives you a great alternative for enabling tilt and swing in the cameras. The design behind the SLR lens is quite simple and thus it results in a curvature of the field of focus. The sharpest area of focus is near the axis.
With the same theory of tilt photography you can achieve selective focus. This is the process emphasizing on a part of the photograph while delimiting the resolution of the other parts of the age. The use of selective focus as discussed above is used primarily for faking scenes as miniature things.
In the era of digital processing it is not a difficult proposition to do miniature faking with the aid of a tool like Photoshop!!