Question

Which lens is used in peepholes of the door?
a) concave lens
or
b) convex lens

Answer 1

a) Door viewers, or peepholes, are small security devices that provide a panoramic view of objects and environments outside doors or walls. The view is created through the use of one or more concave lenses inside the device which minimizes the proportions of specific objects and gives a wide overview of an entire area.