A variation of macrophotography involves using the scanner to produce stereoscopic or "3D" images of small objects. This is made possible because of the optical system of a typical scanner, which uses prisms to put the sensor at an optical distance from the glass of 3 to 4 feet, allowing a small sensor to cover the entire width of the bed, while keeping the bed physically shallow. This also gives better than expected depth of field, and introduces a certain amount of parallax when the same object appears at different positions on the bed. This allows the generation of stereo pairs, much like the "shift" technique where a single camera is shifted to produce right and left views of a still life scene.