Optical designers often choose between converging and diverging lenses depending on the purpose of the device.
Consider the two unrelated devices described below.
Device 1: A portable projector uses a single lens to display an enlarged image of a bright smartphone screen onto a wall several meters away.
Device 2: A residential front-door peephole allows a homeowner standing about 20 cm behind the door to view a wide field of view outside while keeping the image upright.
(1) Identify which lens type (converging or diverging) is appropriate for Device 1. Explain how that lens type satisfies both the orientation requirement and the ability to place a real image on a distant wall.
(2) Identify which lens type is appropriate for Device 2. Explain how that lens type meets the design goal of providing a wide field of view while producing an upright virtual image for the observer inside.
(3) Compare and contrast the behaviour of parallel incident rays in the two lens types you selected and relate this behaviour to the different functional goals of Devices 1 and 2.