Paralleling technique obeys the following law:

The paralleling technique is the preferred method for making intraoral radiographs. It derives its name as the result of placing the image receptor parallel to the long axis of the tooth. This procedure minimizes image distortion. PARALLELING TECHNIQUE: The central concept of the paralleling technique (also called the right-angle technique or long-cone technique) is that the X-ray receptor is supported parallel to the long axis of the teeth, and the central ray of the X-ray beam is directed at right angles to the teeth and receptor. This orientation of the receptor, teeth, and central ray minimizes geometric distortion and presents the teeth and supporting bone in their true anatomic relationships. To reduce geometric distortion, the X-ray source should be located relatively distant from the teeth. The use of a long source-to-object distance reduces the apparent size of the focal spot, thus increasing image sharpness, and provides images with minimal magnification. The paralleling method works equally well for film, CCD or CMOS sensors, or storage phosphor plates.