By placing a mirror behind a tank of water one can produce multiple images of an object, depending on the angle from which it is being viewed. These results are caused by the combined effects of the reflection from the mirror and the refraction of the light through the water. One of the most interesting uses of mirrors was that of a spherical mirror used for robot navigation. Consider a robot with a camera located above a spherical mirror who is trying to navigate through halls and doorways. The spherical mirror produces a distorted 360 degree image of a corridor.
Vertical lines become slanted lines and horizontal lines become segments of circles.
The robot can maneuver down the middle of a hallway by keeping the images of both sides equal distant, and through a doorway by locating the correct features in this distorted image. In human vision the number of pixels in the center of the image is higher than in the peripheral view, while in the typical camera it is uniform over the entire film area. Special lenses which more closely resemble the human eyes can be designed by combining different projections in different areas of the lens. Standard projection is used for the center, log projection for the middle and spherical projection for the periphery. Such a lens is called a foveated wide angle lens, because it provides a wide periphery view and a high resolution fovea image.