DK Science: Cameras
A camera is a device that records pictures. It consists of a sealed box that catches the light rays given off by a source. A lens at the front of the camera brings the light rays to a focus and makes the picture seem closer or further away. Traditional cameras store pictures in a chemical form using PHOTOGRAPHIC FILM. Modern DIGITAL cameras store pictures electronically.
The simplest camera is a small box with a tiny hole in its front wall and a piece of photographic film taped inside its back wall. Light rays cross as they travel between the object and the film, passing through the pinhole. All photographic images are small, upside down, and back to front when inside the camera.
The lens on this camera captures light rays and focuses them. A mirror in the centre of the camera reflects light from the lens into the viewfinder. When a photo is taken, the mirror flips out of the way and light from the lens briefly travels through the camera to the film at the back. The film records an image of the view through the lens.
The oldest surviving photograph was taken by French physicist Joseph Niépce (1765–1833) in 1827. Instead of using photographic film, he used a piece of pewter metal covered with a tar-like substance called bitumen. Light had to enter his primitive camera for eight hours to take the photograph.
French painter Louis Daguerre (1787–1851) invented a much better method of taking photos in 1839. Known as a daguerrotype, it caught images on silver plates coated with a silver-based chemical that was sensitive to light. Taken in just a few minutes, they were clear and showed good detail.
Also in 1839, British inventor William Henry Fox Talbot (1800–1877) took the first ever photograph on paper. Using a different process to Daguerre’s, his cameras captured a reverse image called a negative. Then he used chemicals to turn this into a final image on paper, called a positive.
A film camera records light on a thin piece of transparent plastic coated with a light-sensitive emulsion. The emulsion consists of crystals of silver compounds in a jelly-like substance called gelatin. When light is allowed to briefly strike the film, it causes a chemical reaction in the emulsion and an image is formed.
Colour films produce colour negatives, in which all the different colours in the image are replaced by their complementary, or opposite, colours. The dark colours appear as light areas and the light ones appear dark.
Colour negatives can be used to make either paper prints or plastic slides like this one. A slide is just like the original colour negative but the colours have been reversed and appear normal.
The image taken by a camera, called a photographic negative, looks very different to what was photographed. It is a strange-looking version of the original scene in which dark and light areas are reversed. If you take a photograph of black ink on white paper, the negative shows white ink on black paper.
An ordinary photograph is a piece of paper onto which a picture has been printed from a negative. A digital photograph is a computerized file in which a picture is made up of a string of numbers. A digital image can be loaded into a computer, edited, printed out, sent by email, or stored on a website.
A digital camera is quite similar to a film camera and has similar components and controls. Instead of film, however, a digital camera has a light-sensitive sensor or microchip inside it called a charge-coupled device (CCD). This sensor turns light rays into a pattern of numbers, and the whole photograph is stored as one very long number.
