was for a long time the only way to produce images. Before digital
imaging, the film was the support analog image production for
over 150 years. Photography is originally the product of a reaction
between light and a chemical support. In the 16th century, we
already knew the light action on silver chloride but it was not
until 1802 that the Englishman Thomas Wedgwood published his
method. In 1819, Sir John Herschel, son of the famous astronomer
and discoverer future infrared rays improves the Wedgwood method.
At the same time,
the French Niepce tackles the same problem and gets his first
"héliographics drawings." He partnered with
a scene-painter concerned about the iconographic reproductive
issues, Jacques Daguerre, but he died too soon to appear in 1838,
the first "daguerreotypes." The first negative and
positive first date of 1839 (the English W.H.Fox Talbot). The
first photographic roll of celluloid in 1889 (American George
Eastman). As to the first color plate look-through in a commercially
viable process has been developed in 1904 by the Lumière
brothers. Note that the first photograph in 1827 had requested
the eight hours exposure time during which the sun had time to
illuminate both sides of buildings.
a film is to make usable the support after the shooting. Five
steps lead to attach images from latent negative to negative
- Transfer of the film in a completely light-tight vessel
2 - Processing and revelation at 20 ° C with water, developer
3 - The stop bath of the developer action at pH 3.5 to 5.5 with
a water with 10% acetic acid or 30% white vinegar
4 - The bath fixer leading to the stabilization of the negative
image with an active agent called thiosulfate
5 - Fuser cleaning for stopping its action
6 - The drying of the film up to 2 hours on a wire in a place
films types and packaging|
A film is composed
of silver nitrate grains. Each grain is very sensitive to light
and is capable of storing light information. In films, it must
however differentiate two types : silver color and silver Black
& White supports because they do not really react the same
way. Nevertheless, they all have many elements in common :
- The support
- The light-sensitive
- Annexes layers
The film resembles
the composition of a printed circuit board with its three annexes
- The abrasion-resistant
the film mechanical attack.
- The antihalation
the light reflected by the support in the emulsion. This stray
light affects the image resolution and contrast.
- The anti-curl
the film curve.
The use of a
film is determined by its characteristics. They influence the
final result of the event as well as its use terms. The main
features are seven in number :
- The rapidity. I.S.O indicates the
emulsion sensitivity to light.
- The granularity. It refers to the size
silver metal agglomerates which form the image. More rapid is
the film and more granularity is important.
- The acutance or microcontraste.
- The exposure
It is the ability of the emulsion to render the extremes luminance
of the subject.
- The contrast
or "gamma". It expresses the emulsion contrast as a function
- The sensitivity
It gives the relative sensitivity of the emulsion to different
- The Schwarzschild
effect or gap in the reciprocity law. Unlike digital imaging, the performance
of the film is not constant as and as exposure time lengthens.
More long exposed to light and must be exposed !
can be practiced with a negative film or a reversal film (slide).
The film conditioned in cartridge (film wound in coil several
views) or on a film plane for a single shot. The most common
format is 24x36 packaged in cartridges with a 135 DX code allowing
the device to read different information about the film (sensitivity,
number of shots and exposure latitude).
The DX code was
in the form of twelve bare or painted metal boxes on the cartridge
body 135. The boxes are read by a series of contacts 12 in the
film unit receptacle. The paint acts as insulation as if there
was or not conductivity of these 12 contacts, the camera was
then able to "guess" himself the film type to print.