Cinematography-Theory-And-Practice

F/STOPS - 1/3 - 2/3 -1 -1 1/3 -1 2/3 -2 -2 2/3 -3 -3 1/3 -3 2/3 -4 -4 1/3REFLECTANCE100% 50% 25% 12% 6%80% 40% 20% 10%64% 32% 16% 8%Table 10.3. The relative relationshipbetween f/stops and reflectance.intervals give the intermediate fc values. For example, the differencebetween 32 fc and 160 fc is 2 1/3 stops.Percentage of Reflection: The ISO scale from 100 on down relatesto percentage of reflection. For example, ISO 100 can represent100%, pure white. Other reflectances, such as 64% and 20%, can thenbe seen to be 2/3 stop and 2-1/3 stops darker than pure white (Table10.3).Shutter Speeds: Referring to the ISO scale (Table 10.2), it can beseen that, for example, 1/320 sec. is 1-2/3 stops faster than 1/100 sec.This can be helpful when unusual combinations of shutter angle andframe rate produce odd effective shutter speeds.LIGHT AND FILMIt is the energy in each photon of light that causes a chemical changeto the photographic detectors that are coated on the film. The processwhereby electromagnetic energy causes chemical changes tomatter is known as photochemistry.All film is coated onto a base: a transparent plastic material (cel-the base, an emulsion is adhered where the photochemistry happens.There may be 20 or more individual layers coated here that are collectivelyless than one-thousandth of an inch in thickness. Some ofthe layers coated on the transparent film do not form images. Theyare there to filter light, or to control the chemical reactions in theprocessing steps. The imaging layers contain sub-micron-sizedgrains of silver halide crystals that act as the photon detectors.These crystals are the heart of photographic film. These crystalsundergo a photochemical reaction when they are exposed to variousforms of electromagnetic radiation — light. In addition to visiblelight, the silver halide grains can be sensitized to infrared radiation.A halide is a chemical compound of a halogen (any of a group of fivechemically related nonmetallic elements including fluorine, chlorine,bromine, iodine, and astatine) with a more electropositive elementor group, in this case silver. Silver halide grains are manufacturedby combining silver nitrate and halide salts (chloride, bromide, andiodide) in complex ways that result in a range of crystal sizes, shapes,and compositions.The unmodified grains are only sensitive to the blue part of thespectrum, and thus are not very useful in camera film. Spectral sensitizersare added to the surface of the grains to make them moresensitive to blue, green, and red light (remember, we’re talking aboutblack-and-white film here). These molecules must attach to the grainsurface and transfer the energy from a red, green, or blue photonto the silver halide crystal as a photo electron. Other chemicals areadded internally to the grain during its growth process, or on thesurface of the grain. These chemicals affect the light sensitivity ofthe grain, also known as its speed — that is, how sensitive to light it is.The speed of an emulsion is quantified by standards set by the ISO(International Standards Organization) or ASA (American Standards Association)rating. ISO is the technically the correct designation, but bytradition, many people still refer to it as ASA. The higher the ISO,cinematography188