Classification and properties Film stock

1 classification , properties

1.1 base
1.2 emulsion
1.3 chemistry
1.4 image record
1.5 physical characteristics
1.6 responsivity
1.7 color temperature

classification , properties

a short strip of undeveloped 35 mm color negative film.

there several variables in classifying stocks; in practice, 1 orders raw stock code number, based on desired sensitivity light.

base

a piece of film consists of light-sensitive emulsion applied tough, transparent base, attached anti-halation backing or rem-jet layer (now on camera films). highly flammable cellulose nitrate used. in 1930s, film manufacturers introduced safety film cellulose triacetate plastic base. amateur film stocks safety film, use of nitrate persisted professional releases. kodak discontinued manufacture of nitrate base in 1951, , industry transitioned entirely safety film in 1951 in united states , 1955 internationally. since late 1990s, release prints have used polyester film stock.

emulsion

the emulsion consists of silver halide grains suspended in gelatin colloid; in case of color film, there 3 layers of silver halide, mixed color couplers , interlayers filter specific light spectra. these end creating yellow, cyan, , magenta layers in negative after development.

chemistry

development chemicals applied appropriate film can produce either positive (showing same densities , colors subject) or negative image (with dark highlights, light shadows, and, in principle, complementary colors). first films darkened light: negative films. later films produce positive image became known reversal films; processed transparent film of type can projected onto screen. negative images need transferred onto photographic paper or other substrate reverses image again, producing final positive image. creating positive image negative film can done scanning negative create computer file can reversed software.

image record

different emulsions , development processes exist variety of image recording possibilities: 2 common of black , white, , color. however, there variant types, such infrared film (in black , white or false color); specialist technical films, such used x-rays; , obsolete processes, such orthochromatic film. generally, however, vast majority of stock used today normal (visible spectrum) color, although normal black , white commands significant minority percentage.

physical characteristics

film classified according gauge , arrangement of perforations— gauges range 8 mm 70 mm or more, while perforations may vary in shape, pitch, , positioning. film distinguished how wound regard perforations , base or emulsion side, whether packaged around core, daylight spool, or within cartridge. depending on manufacturing processes , camera equipment, lengths can vary anywhere 25 2000 feet. common lengths include 25 feet 8 mm, 50 feet super 8, 100 , 400 feet 16 mm, 400 , 1000 feet 35 mm, , 1000 65/70 mm.

responsivity

a critical property of stock film speed, determined asa or sensitivity light listed measurement on raw stock must chosen care. speed determines range of lighting conditions under film can shot, , related granularity , contrast, influence of image. stock manufacturer give exposure index (ei) number equal asa recommend exposing for. however, factors such forced or non-standard development (such bleach bypass or cross processing), compensation filters or shutter angle, intended under- , over-exposure may cause cinematographer rate stock differently ei. new rating not change stock itself — merely way of calculating exposure without figuring out compensation after each light reading.

color temperature

another important quality of color film stock in particular color balance, defined color temperature @ accurately records white. tungsten lighting defined @ 3200 k, considered warmer in tone , shifted towards orange; daylight defined @ 5600 k, considered colder , shifted towards blue. means unfiltered tungsten stock normal shot under tungsten lights, blue if shot during daylight. conversely, daylight stock shot in daylight normal, orange if shot under tungsten lights. color temperature issues such these can compensated other factors such lens filters , color gels placed in front of lights. color temperature of film stock indicated next film speed number — e.g. 500t stock color film stock asa of 500 , balanced tungsten light; 250d have asa of 250 , balanced daylight. while black-and-white film has no color temperature itself, silver halide grains tend more responsive blue light, , therefore have daylight , tungsten speeds — e.g. kodak s double-x stock rated 250d/200t, since tungsten light give less exposure equivalent amount of daylight.