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Prior To The Dawn of Motion Pictures

Writing With Light

Man’s knowledge regarding the changes that light causes in some metal compounds dates back to times prior to the birth of photography. Research in this field led Ritter to the discovery of ultraviolet light, and records exist of data from experiments conducted beginning in the 18th century regarding using light directly in reproducing images, the slowness of the reaction and, above all, the lack of a system capable of setting the image thus obtained, halting the blackening of the metal solution, having put an end to these pursuits.

Black & White Pictures

If the research, which led to the birth of photography, was based on the blackening of metal compounds under the effects of light, the picture, which could be obtained, using this type of processes, had to be made visible as a result of the difference between the different areas blackened to greater or lesser degrees. This would be a black and white picture.

Given that the blackening reaction is much faster when the higher-energy areas of the spectrum are being employed, the initial emulsions were sensitive solely to ultraviolet and blue light (orthochromatic). The panchromatic emulsions, which were sensitive to the entire spectrum, required the adding of organic dyes to be sensitive to green, yellow and red. These emulsions first began to be developed toward the end of the 19th century, the first commercial panchromatic emulsions being marketed in 1906. Currently, there are emulsions that are sensitive way into the infrared portion of the spectrum.

Silver Bromide

The initial attempts at taking photographs were made using silver nitrate solutions, but these pursuits soon focused on the use of other salts (iodines or bromides), which would earn a reputation as being the most suitable beginning in the mid-19th century. Silver bromide combined with small amounts of iodine, forming crystals nearing one millimicron in diameter, which contain hundreds of thousands of metal ions, is the most important active ingredient in the emulsions used in the filmmaking industry.

Latent Image

When light strikes an iodine-silver bromide crystal, some halide ions break down in a number depending upon the amount of light, which strikes each crystal, releasing metallic silver. Although all of the ions contained in each crystal could be broken down if enough light were available, under the working conditions involved in photography, only some photons have an effect on each crystal and only some of the silver ions will be converted into metallic silver, forming a very faint image, absolutely invisible, of the light received. This image is known as a latent image.

Speed & Developing

Following exposure to the light, films undergo two chemical processes which will act on the crystals which have been struck by the light, followed by those which were not involved in the forming of the latent image.

The first of these two processes, developing, employs reducing agents such as hydroquinone, MetolÔ and PhenidoneÔ. The silver resulting from the light print acts as an inducer and catalyst of a change in which all of the silver ions in the crystals containing latent image will be turned into black metallic silver. The extremely minute dimensions of the latent image will be multiplied thousands of times over, and the build-up of metallic silver will become visible.

In the second of these two processes, that is, the fixing process, products are used to dissolve the silver bromide in all of the crystals, which were not sensitised by the light. This process will make it possible for the film to keep from continuing to turn black on being exposed to further light, thus fixing the picture taken photographically.

Film Speed, Definition and Grain

The ability to reproduce the finer details of the objects photographed (defining-power) on film and how fast the exposure can be made at a certain degree of level (speed) are linked quite closely to one another.

An emulsion’s speed depends on the amount of light it requires to form a latent image, which is truly that of the image being photographed. In conjunction with this, the definition, which can be achieved in a photograph, depends, first of all, on the size of the halide crystals and on how they are spread throughout the entire layer of the emulsion.

The larger the halide crystals, the greater their probabilities of being struck by a quantum of light (the faster-reacting the emulsion will be), but, on going through the emulsion, the light sensitises many layers of crystals which will grow in size up to the point of forming black grains readily visible to the naked eye, lowering the film’s defining-power.

In the areas of the emulsion, which were brightly illuminated, a latent image can form in all of the crystals, which will react during the developing process to then turn into "silver grains" providing the area in question with a dense opaqueness. But the density and "richness in detail" of the image is created in the "gray areas" and will depend upon the number and the size of the crystals converted.

Convenience

Early photographic plates had to be "prepared" immediately prior to use and to be developed immediately thereafter. It was not until the mid-19th century that stable emulsions came out that would retain their light-sensitive properties from the time of manufacture until the time of use over weeks, months and even years and would afford the possibility of postponing processing for reasonable lengths of time.

Emulsions

Many different approaches were employed to solve all of the problems involved.

As of 1851, a nitrocellulose derivative, pyroxilin, was used to manufacture wet collodion emulsions, achieving major speed-related improvements. Ten years later, a then dry form of this same substance would be used to achieve the first truly practical photographic plates, which did not have to be prepared immediately prior to use. In 1852, gelatins began to be used as emulgents for silver bromide and, in short, silver-bromide gelatin would become the substance used worldwide in photographic emulsions.

Gelatins

Gelatins are natural organic substances, which are found in the skin and bones of many animal species and which, when properly treated, can be employed for many different uses (in the field of photography, they have also been used for manufacturing filters). The initial use of gelatins as emulgents for photographic emulsions became the norm, given that in addition to the fine consistency and flexibility they provide upon solidifying, they also possess the highly important property of containing certain active impurities which moderate the light-sensitivity of the metallic salts.

Slime

Gelatins are used in biology as culture media for many different germs and bacteria, these being germs and bacteria which can also multiply in photographic emulsions under the right moisture-related conditions, and although "killing them" can sometimes be easy, permanent damage is done to the transparency of the gelatins on which they feed. Thousands of films have been damaged or completely destroyed as a result of this property of gelatins.

Positive è Negative è Positive

Light-Dark Reversal

The brightness of objects is directly proportional to the amount of light they emit or are able to reflect, and as far as photographic emulsions are concerned, the resulting blackening is also proportional to the amount of light absorbed. Hence, the image, which will form in the emulsion, will process light in the form of darks. This processing of white into black is known as a reproduction in negative. Of course, the reversal of white and black leads to many aspects of the image becoming unrecognisable, and negatives are not accepted as being actual facsimiles. But on repeating the imaging process by printing a second picture from the negative, the process of reversing the light values will be repeated to make them the same as those of the true-life image captured on the negative. This second image is referred to as a reproduction in positive print.

Colour Reversal

The colour-subtracting emulsions go through the same reversal of brightness as the black and white ones, but given that these emulsions process on the frequencies for red, blue and green separately, the change they cause in their additive complementary colours (cyan, yellow and magenta) will additionally reflect these reversals of light separately.

So a black image will show up in white on a subtracting negative just like on a black and white negative, but a dark red image will show up in light shades of cyan.

Negative & Print on One Same film

In 1814-1837, Niepce and Daguerre invented the daguerreotype, in which the negative and the print were made one after the other on the same plate. Other systems have continued using the same negative/print relationship. In these systems, the image is first developed as a negative to then be destroyed by means of a bleaching process, and those areas containing no image are exposed again or undergo a chemical blackening to be developed as prints.

Original Negative & Prints

Producing the final print on the same film as the negative may entail quality-related advantages but leads to the process of making several prints from each negative being higher-priced and more highly involved. In the filmmaking industry, this method has been relegated to amateur or not highly specialized uses such as for newspaper articles and prints to be kept on file or sold. The methods for making several prints from one single negative have been based on shining light through transparent negatives to make prints on other stock. Hence, the original camera negative is then the master film, and the prints are the copies made as release prints.

Flexible, Transparent Media

Glass

The first medium was that of metal plates, but the need to avail of stable, transparent materials resistant to chemical compounds gave rise to the use of glass and also of paper coated with different substances.

Glass is a material, which possesses good optical properties and is reasonably inexpensive, yet it is fragile and heavy. The machines able to take several plates were expensive and hard to handle, and although glass would continue to be used well into the 20th century, it never met with full acceptance.

Nitrocellulose

Nitrocellulose came into being in 1846 as the result of the nitrating of a cellulose solution in the presence of sulphuric acid and is highly explosive, its instability having led to its failure as a smokeless powder due to its being set off at the least rise in pressure. Twenty years later, one improvement after the other led to a non-explosive derivative, pyroxilin, which took on plastic properties as the result of the adding of camphor, and later the development of different types of nitrocellulose (trinitrates), nitrated to a very low degree (11%) and highly stable.

CelluloidÔ, a brand name for plasticized nitrocellulose, was the first man-made plastic. Possessing excellent mechanical properties and being flexible, Celluloid can be used in rolls, possesses a high degree of tensile strength and does not readily absorb moisture. When cold, it can be machined using cutting tools; and when heated, it can be moulded or shaped into very thin, regularly shaped sheets by extrusion. In thick sheets, it is somewhat yellowish in subtracting, but in the thin sheets used in the filmmaking industry (approx. 140 microns thick) is almost completely transparent, allowing nearly 95% white light to shine through.

In 1889, George Eastman incorporated Celluloid into his "Kodak" photography system as a film base and, one year later, Eastman and Dickson set out on the collaboration, which would result in the films used in Edison’s "Kinetograph" being made of Celluloid.

A Self-Destructing Material

Developed based on research aimed at coming up with new explosives, nitrocellulose still possesses a major degree of the chemical instability typical of these materials, and although it is not in any way explosive, this instability taken on several forms. Nitrocellulose ignites at a temperature of solely 160ºC and can even burst into flame on its own since that temperature can be reached inside a rolled film stored at over 40ºC when contraction causes the pressure between the wound loops of film to rise.

At relatively high temperatures and high degrees of relative humidity, nitrocellulose undergoes chemical breakdown, the molecular bonds breaking apart and freeing nitrate groups (NO₂) which will hasten the breakdown process, giving rise to smouldering. Hence, the film hardens, contracts and becomes brittle. As a last resort, the increasing rate at which the molecules break apart will completely depolymerise the plastic, turning it into powder. Thousands of nitrocellulose films have already been lost forever, as the result of fires or rot, and all film stock of this type will self-destruct in a not too distant future.

Acetate/ Safety Film

The major degree to which nitrocellulose is flammable led to research having been done aimed at coming up with other plastics which would not entail this major drawback. The best results were achieved by acetylizing instead of nitrating the cellulose solution.

Cellulose Diacetate

Starting in 1923, this plastic was first used in the manufacture of film stock. Its optical and mechanical properties were comparable to those of nitrate, but its moisture absorbency, which was much greater than that of nitrate, failed to guarantee films satisfactorily retaining their size-related aspects, for which reasons it was relegated to 16mm and 9.5mm home movies, for which non-flammability involved a major point involved in the decision to purchase.

Cellulose Triacetate

The year 1941 marked the invention of a new acetate, known as triacetate, which was stable enough to take the place of Celluloid and also entailed the added advantage of being inflammable.

Cellulose acetates are highly permeable to steam and to numerous gases, but this permeability lessens the higher the degree of acetylizing involved. Triacetate is the most stable acetate and, having a moisture-absorption index which is 2-3 times higher than nitrate, retains its physical properties similar to those of nitrate and even shows a greater degree of size-related stability. Under the effects of light, triacetate has been revealed to tend to yellow, but under the standard conditions of use for film, these properties are of no major importance. In 1942, film first began to be manufactured using this type of plastic, and it was around 1950 when the Celluloid production lines started closing down, all motion picture film stock starting to be manufactured using acetates shortly thereafter.

A Poor Safe-Storage Material

Cellulose triacetate was considered to be safety film due to its not being self-igniting having a flash point of 430ºC. Its chemical combustion processes at temperatures below its flash point are slow, and in addition thereto, the plasticizer most often used in its manufacture, 3-phenylphosphate, contributes to smothering the flames in the event of its igniting.

In chemical terms, triacetate is highly unstable. Under high humidity and high temperature conditions, triacetate triggers a hydrolysis reaction in which the acetic groups (OAc) bond with hydrogen to form acetic acid (CH₃COOH), which acts as a catalyst of yet further hydrolysis processes, modifying the structure of the molecular bonds and weakening and deforming their dimensions and transparency up to the point of destroying their plastic properties. The "vinegar syndrome" poses a serious threat to keeping this stock intact, particularly in warm, humid climates.

Polyester Stock

Invented in the forties, it was hard for a long time to get polyester providing the necessary degree of transparency and to manage to get photographic emulsions to adhere to it, but by late sixties it was being widely used in the manufacture of magnetic stock and in Super 8 mm-format film. Polyester is currently being used in all types of raw stock.

Its great breaking strength comprised another drawback for its acceptance in industry. For 35mm or 16mm motion pictures, if the film gets caught up in the projectors, the machine shafts and moving parts can be damaged due to the tensile strength, which this film is capable of withstanding prior to breaking. The possibility of these accidents has been found to be further heightened by this plastic’s tendency to build up static electricity. Polyester is highly stable as regards its dimensions (on requiring no plasticizers) and, like triacetate, is not self-igniting, its flash point being approx. 480ºC. Polyester’s high degree of resistance to industrial solvents and acids has made it necessary to develop heat-welding systems for splicing purposes.

Comparison of Nitrate, Triacetate and Polyester Properties

	Tensile Strength (kg/cm2)	Ultimate Elongation (%)	Tear Resistance (kg/cm2)	Moisture Absorption (24 hours / 20º)	Gas Permeability	Flammability	Acid and Alkali Resistance	Resistance to Micro-organisms
Nitrate	680-750	30-40	-----	1.5-2	high degree	very high degree	low degree	-----
Triacetate	612-1088	10-40	3.7-26.9	3.5-4.5	high degree	slow	low degree	depending on plasticizer
Polyester	1160-1700	70-130	33.7	0.8 (168 h./25ºC)	very low degree	very low degree	no attack	very good

Lenses & Lens Assemblies

In order for it to be possible to "write with light", the light must copy or "draw" the outline of the image to be copied on the emulsion-coated surface to the utmost degree of precision.

For contact reproductions, on the surface of the negative coming into contact with the raw emulsion, the light shining through the master can solely mark or "draw" the image thereon, but if the object which is being printed is not touching the raw emulsion, it will be necessary to employ devices to selection and focus the rays of light so that the emulsion can "draw" the image.

Pinhole Camera Lenses

The simplest device possible is a pinhole in the front of the "camera obscura", which filters out the light, allowing solely that the striking the front cone to shine through. These pinhole stenoscopic cameras focus to the same degree of quality for any depth of field, but only achieve a highly irregular degree of definition.

Lenses

A lens is a transparent, mirror-finish (or magnetic) device, which is capable of changing the direction in which rays of light (or of electromagnetic energy), which strike or pass through it will flow.

Diverging & Converging Lenses

The basic classification for almost all types of lenses is in keeping with the deviation, which they cause to a set of parallel rays of light, which strike or shine through the lens. If the effect of the lens is that of shortening the spacing between the rays and concentrating brightness, they are referred to as converging lenses, diverging lenses being those which widen the space between the rays, dispersing the light and dimming brightness. Lenses are usually regularly shaped, and when the light strikes them in parallel, it is concentrated or seems to disperse from what is known as focus (F).

For converging (or positive) lenses, the focus point is an actual, physical point located behind the lens. For diverging (negative) lenses, the point of focus is solely virtual point and is located in front of the lens. The lenses most often used are spherical lenses, the working surfaces of which are ground into the shape of rounded caps. Spherical mirrors and cylinder or step lenses and prisms are also used.

Refraction & Dispersion

Light changes speed and direction on shining through materials of different densities. This phenomenon, known as refraction, is stated in the form of a value which differs according to the type of transparent material in question and which relates the speed of the light to the deflection of its path on shining through materials of different densities.

Water has a 1.33 refraction index, that of glass falling within the 1.45-1.95 range. The lightest-weight types of optical glass, crown glass, have refractions of over 1.5, and heavy flint glass of over 1.75.

Lens Effects

Out in open space, light travels at the same speed for any wavelength, but when these waves flow through matter, their speed will vary depending upon their length.

When white light shines through a lens, the violet light waves undergo the greatest possible degree of deflection, the red light undergoing only a minimal degree. The gap between red and violet is known as dispersion and, although it is related to the density of each individual type of matter, it also depends upon its chemical composition of the matter in question.

For transparent lenses, the speed and direction of the light undergoes many different changes on entry, on shining through the lens and on exiting. On shining through the first surface and entering inside, the speed is slowed down as a function of density of the lens in question (refraction index), and the direction of the light changes in keeping, first of all, with the angle of reflection which the light and the lens surface form at each point and, secondly, individually for each wavelength, the speed at which the waves shine through the glass depending upon the chemical composition of the glass in question (dispersion index). After shining through the second surface, the light regains its initial speed, but changes direction once again, individually for each colour, depending upon the angle at which it strikes the surface through which it exits.

Aberrations

On deflecting and dispersing the light, lenses change images, distorting their features. The change in speed and the dispersion of light give rise to colour aberrations. The red image is larger (axial aberration) and takes shape much further away from the lens (longitudinal aberration) than violet, all other colours shaping their images between these two ends of the spectrum.

Geometrical aberrations are caused by the shape of the lenses and by the angle at which the light strikes each point on the lens surface.

Spherical aberration, especially important with regard to the lens axis, shapes images progressively further away from the lens.

The aberration known as coma distorts the image in relationship to the distance between the line of sight and each point of the image on the lens. Stigmatism distorts the ring of light by turning it into an oval.

Compound Lenses & Lens Assemblies

In 1733, C. Moor combined a converging crown glass lens providing a low degree of dispersion with a diverging flint glass lens providing a high degree of dispersion, thus having achieved an assembly, which lowered the degree of chromatic aberration.

The achromatic lens gave rise to the building of lens assemblies capable of correcting aberrations.

To correct aberrations by combining different lenses one must bear in mind that the object/image reflected on each consecutive lens has been modified by the previous lens and thus design the consecutive lenses to offset the deviations in colour such that they will characterize the object/image reflected thereon.

No lens exists which will do away with all of the five aberrations at the same time, and when designing lens assemblies, one must consider their intended use and rule out the most highly damaging ones. Although a camera can be built with a simple lens, much better features are achieved by combining lens assemblies, which will afford the possibility, for example, of selecting the size of the object to be photographed and the size proper of the negative, whilst also improving the conditions of brightness, sharpness and depth of the image.