What is motion picture ﬁlm? The American National Standards Institute (ANSI) describes it as “a thick ﬂexible strip of plastic, complying with a dimensional standard as deﬁned within, whose use is speciﬁc to the process of manufacturing a motion picture.” That deﬁnition leads to about a dozen pages of further deﬁnitions about various aspects of motion picture ﬁlm. For our purposes, let’s take a look at how ﬁlm is made, and how an image is formed on that ﬁlm.
THE STRUCTURE OF FILM
Film is made up of layers, and it’s the combination of these layers that give each ﬁlm its character. Motion picture ﬁlm consists of a transparent support ﬁlm base, a light-sensitive emulsion, and a number of layers coated on both sides. Some layers are di erent from those coated on still ﬁlm and are designed to help motion picture ﬁlm travel smoothly through the camera.
The supporting layer in ﬁlm is called the base. This base has to be transparent (with some optical density), free from imperfections, chemically stable, insensitive photographically, and resistant to moisture and processing chemicals, while remaining mechanically strong, resistant to tearing, ﬂexible, and dimensionally stable. Three plastics have been widely used as a motion picture ﬁlm base: • Cellulose nitrate was the ﬁrst material used. Discontinued in the 1950s because it was highly ﬂammable, cellulose nitrate is chemically unstable if stored in conditions that are too damp (it can decompose) or too hot (it can self-ignite). • Cellulose acetates were developed to replace nitrate. Cellulose triacetate, called safety base, is much safer to use and store than nitrate. Most current KODAK and EASTMAN Motion Picture Films are coated on a cellulose triacetate base. • Polyester base is used for all print ﬁlms, most duplicating ﬁlms, and some specialty ﬁlms. Polyester is stronger and wears better than triacetate. Polyester’s storage life is up to ten times that of acetate. ESTAR Base, a polyethylene terephthalate polyester, is used for some KODAK and EASTMAN Motion Picture Films (usually intermediate and print ﬁlms) because of its high strength, chemical stability, toughness, tear resistance, ﬂexibility, and dimensional stability. The greater strength of ESTAR Base permits the manufacture of thinner ﬁlms that require less storage room. ESTAR Base ﬁlms and other polyester base ﬁlms cannot be successfully spliced with readily available commercial ﬁlm cements.
These ﬁlms are spliced with a tape splicer or with a splicer that uses an ultrasonic or an inductive heating current to melt and fuse the ﬁlm ends.
The most fundamental layer in a ﬁlm is the emulsion layer(s), adhered to the base by means of a binder. The emulsion is the photographic part of the ﬁlm, and as noted from ANSI, “consists of dispersions of light-sensitive materials in a colloidal medium, usually gelatin, carried as a thin layer(s) on a ﬁlm base.” Emulsion is made by dissolving silver bullion in nitric acid to form silver-nitrate crystals. These crystals are dissolved and mixed with other chemicals to form silver-halide grains, and then suspended in the gelatin emulsion coating. The size and degree of light sensitivity of these grains determines the speed or amount of light required to register an image. The faster the ﬁlm, the greater the apparent “graininess” of the image. In 1991, The Motion Picture and Television Imaging division of Eastman Kodak Company received an OSCAR from the Academy of Motion Picture Arts and Sciences for incorporating KODAK T-GRAIN® Emulsion Technology into motion picture ﬁlms. This term, now familiar among all types of ﬁlm, describes ﬂat silver crystals that capture more light without an increase in size. In color ﬁlms, three dye layers register various parts of the color, one on top of another, for the full color e ect—in cyan, magenta, and yellow dyes. In fact, each color may have up to three layers...