A camera is an optical instrument that records images that can be stored directly, transmitted to another location, or both. These images may be still photographs or moving images such as videos or movies.
The term camera comes from the word “Camera Obscura” (Latin for "dark chamber). The modern camera evolved from the camera Obscura & functioning of the camera is very similar to the functioning of the human eye.
Camera Obscura is the natural optical phenomenon that occurs when an image of a scene at the other side of a screen (or for instance a wall) is projected through a small hole in that screen as a reversed and inverted image (left to right and upside down) on a surface opposite to the opening. The surroundings of the projected image have to be relatively dark for the image to be clear. Camera Obscura with a lens in the opening has been used since the second half of the 16th century and became popular as an aid for rawing and painting. The camera Obscura box 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.
A twin-lens reflex camera (TLR) is a type of camera with two objective lenses of the same focal length. One of the lenses is the photographic objective or "taking lens" (the lens that takes the picture), while the other is used for the viewfinder system, which is usually viewed from above at waist level.
A single-lens reflex camera (SLR) is a camera that typically uses a mirror and prism system (hence "reflex" from the mirror's reflection). SLR permits the photographer to through the lens and see exactly what will be captured. When the shutter button is pressed on a mechanical SLR, the mirror flips out of the light path, allowing light to pass through to the light receptor and the image to be captured.
