"Camera obscura" can also refer to analogous constructions such as a box or tent in which an exterior image is projected inside. Camera obscuras with a lens in the opening have been used since the second half of the 16th century and became popular as aids for drawing and painting. The concept was developed further into the photographic camera in the first half of the 19th century, when camera obscura boxes were used to expose light-sensitive materials to the projected image.