A camera is a device used to capture images, as still photographs or as sequences of moving images (movies or videos). The term as well as the modern-day camera evolved from the camera obscura, Latin for "dark chamber", an early mechanism for projecting images, in which an entire room functioned as a real-time imaging system. Cameras may work with the light of the visible spectrum or with other portions of the electromagnetic spectrum. A camera generally consists of some kind of enclosed hollow, with an opening or aperture at one end for light to enter, and a recording or viewing surface for capturing the light at the other end. Most cameras have a lens positioned in front of the camera's opening to gather the incoming light and to focus the image, or part of the image, on the recording surface. The diameter of the aperture is often controlled by a diaphragm mechanism, but some cameras have a fixed-size aperture.