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.
MILESTONES OF PHOTOGRAPHY
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.
In 1861, the distinguished British physicist James Clerk Maxwell
(1831–1879) became the first person to make a colour photograph. He took
three photographs of this tartan ribbon in three separate colours, then added
them together to make a single colour picture.
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.
