[L.] An optical instrument.
In its simplest form it consists of a rectangular box fitted at one end with a lens and at the other end with a plane mirror, inclined at an angle of 45° to the horizon. When the lens is directed to any object, the rays of light, after passing through the lens, are reflected from the mirror, and form an image on a plate of glass at the top of the box, where they may be observed and sketched. Instead of the box it is usual to have . a kind of tent surrounded with curtains to keep out the light. There are various forms of the camera now in use for taking photographic negatives, the photographic camera being an adaptation of the camera obscura, which is fitted at the back for the introduction of a sensitized plate or film, so as to receive the image of an object or scene in front of the lens.