Tilt Shift lens
A tilt & shift lens is a lens that can correct the depth of field and vertical lines. By adjusting the tilt mechanism, you can make sure the whole subject or only a specific part of the subject remains sharp. The shift mechanism allows you to retract distorted vertical lines. This distortion is caused by the angle from which is photographed and occurs mainly in wide-angle lenses. By using the shift mechanism, you change the way the image falls on the sensor, so that vertical line is really vertical.