Camera

A camera is a device used to reproduce images photographically, by sensing and recording light against a plane. This is done using either photo-sensitive chemical substances or charge-coupled devices (CCDs).

Parts of the camera
Attached to the camera body is a lens which is used to focus the image on the film or CCD plane. The lens can have a variable aperture, which lets a certain amount of light go through to the body of the camera. Inside single-lens reflex still cameras, there is a mirror between the lens and the light-sensitive film or CCD. When the photograph is taken, the mirror flips up so the light can go through, then flips back down so the light hits the mirror and goes up to the eye-piece or focusing display. Mirrors are not used in video photography, since the image is being sensed continuously. For modern compact digital cameras, a mirror is not used. In a twin-lens reflex system, the mirror is present, but it need not flip, since the focusing lens produces a separate image from the objective lens.

A camera can be built without the use of a lens: a pinhole camera can be constructed simply by producing a very small hole in, say, a piece of cardboard. The aperture of the lens dictates the amount of time the exposure needs to produce an image on the film or CCD. If the exposure is for too long, the material will "white-out" and the image will not be distinguishable from the white. If the exposure is not for long enough, the material will not get enough light and no image will form. The aperture of the lens, that is the size of the hole, is measured in terms of $$f$$-numbers. The larger the number, the smaller the hole. The smaller the aperture, the longer the depth of field - the amount of latitude in focus will be. This is often used in photography for creative effect. If one is taking a photograph of a person, a small depth of field (achieved by large aperture) will 'pull' the subject away from the background.

Choosing a camera
There are a wide variety of cameras that are available on the market today, serving a wide range of niches. Before purchasing a still camera, there are important questions that you should ask:
 * Does the camera produce an image that is of an adequate size for what you wish to do with it? With a digital camera, the number of megapixels measures the amount of data that gets stored for each exposure. A camera that produces 1 or 2MP images is fine if you only intend to take images to put up on the Web. For producing images that are of a larger size, one needs to get a camera with a higher megapixel count. In film photography, this is less of an issue: most cameras use 35mm film, which will produce a good image for most consumer uses. APS cameras are unsuitable for taking photographs that need to be enlarged above small amount. Medium and large format film cameras can be used if the image needs to be enlarged beyond about A3 size.
 * Are the lens optics good? Poor-quality lenses can produce 'barrelling' or other visible forms of aberration. Good quality lenses can often cost a lot of money, so don't expect to get Ansel Adams-style results from a cameraphone or low-end consumer camera.