Two or more views of a scene are printed on a thermoplastic sheet of lenticular (concave) lenses that look like parallel ridges (see below). In order to align the image to the lens array ...

the lens being too thick and curved - so that light is focused in front of the retina. Short-sightedness can be corrected by placing a concave lens in front of the eye, as shown in the diagrams below.

Draw a ray which passes from the object through the centre of the lens. Some ray diagrams may also show a third ray. Peep holes contain concave lenses. They are set into doors so the occupant can ...