Photographic film

Instead, a very short exposure to the image formed by a camera lens is used to produce only a very slight chemical change, proportional to the amount of light absorbed by each crystal.

Unmodified silver halide crystals are sensitive only to the blue part of the visible spectrum, producing unnatural-looking renditions of some colored subjects.

[12] The sensitivity (i.e., the ISO speed) of a film can be affected by changing the length or temperature of development, which would move the H&D curve to the left or right (see figure).

The antihalation layer, besides having a black colloidal silver sol pigment for absorbing light, can also have two UV absorbents to improve lightfastness of the developed image, an oxidized developer scavenger, dyes for compensating for optical density during printing, solvents, gelatin and disodium salt of 3,5- disulfocatechol.

Here the oil droplets act as a surfactant, also protecting the couplers from chemical reactions with the silver halide and from the surrounding gelatin.

[26] Some manufacturers manufacture their films with daylight, tungsten (named after the tungsten filament of incandescent and halogen lamps) or fluorescent lighting in mind, recommending the use of lens filters, light meters and test shots in some situations to maintain color balance, or by recommending the division of the ISO value of the film by the distance of the subject from the camera to get an appropriate f-number value to be set in the lens.

Films of ISO 800 and greater are thus better suited to low-light situations and action shots (where the short exposure time limits the total light received).

Professional photographers of static subjects such as portraits or landscapes usually seek these qualities, and therefore require a tripod to stabilize the camera for a longer exposure.

A professional photographing subjects such as rapidly moving sports or in low-light conditions will inevitably choose a faster film.

Instant photography, as popularized by Polaroid, uses a special type of camera and film that automates and integrates development, without the need of further equipment or chemicals.

This process is carried out immediately after exposure, as opposed to regular film, which is developed afterwards and requires additional chemicals.

These films generally require special equipment; for example, most photographic lenses are made of glass and will therefore filter out most ultraviolet light.

Exposure and focusing are difficult when using UV or IR film with a camera and lens designed for visible light.

For example, Agfa 10E56 holographic film has a resolution of over 4,000 lines/mm – equivalent to a pixel size of 0.125 micrometers – and an active dynamic range of over five orders of magnitude in brightness, compared to typical scientific CCDs that might have pixels of about 10 micrometers and a dynamic range of 3–4 orders of magnitude.

The first known version of this process was patented in the United States in 1975, using half-silvered mirrors to direct the readout of a digital clock and mix it with the light rays coming through the main camera lens.

Although fragile and relatively heavy, the glass used for photographic plates was of better optical quality than early transparent plastics and was, at first, less expensive.

As a result, the relative tonal values in a scene registered roughly as they would appear if viewed through a piece of deep blue glass.

In 1873, Hermann Wilhelm Vogel discovered that the spectral sensitivity could be extended to green and yellow light by adding very small quantities of certain dyes to the emulsion.

The instability of early sensitizing dyes and their tendency to rapidly cause fogging initially confined their use to the laboratory, but in 1883 the first commercially dye-sensitized plates appeared on the market.

These early products, described as isochromatic or orthochromatic depending on the manufacturer, made possible a more accurate rendering of colored subject matter into a black-and-white image.

New and improved sensitizing dyes were developed, and in 1902 the much more evenly color-sensitive Perchromo panchromatic plate was being sold by the German manufacturer Perutz.

[12] The initial take up of digital cameras in the 1990s was slow due to their high cost and relatively low resolution of the images (compared to 35mm film), but began to make inroads among consumers in the point and shoot market and in professional applications such as sports photography where speed of results including the ability to upload pictures direct from stadia was more critical for newspaper deadlines than resolution.

Consequently, photographers demanding higher quality in sectors such as weddings, portraiture and fashion where medium format film predominated were the last to switch once resolution began to reach acceptable levels with the advent of 'full frame' sensors, 'digital backs' and medium format digital cameras.

[55] This period wreaked havoc on the film manufacturing industry and its supply chain optimised for high production volumes, plummeting sales saw firms fighting for survival.

Agfa-Gevaert's decision to sell off its consumer facing arm (Agfaphoto) in 2004, was followed by a series of bankruptcies of established film manufacturers: Ilford Imaging UK in 2004, Agfaphoto in 2005, Forte in 2007, Foton in 2007, Polaroid in 2001 and 2008, Ferrania in 2009, and Eastman Kodak in 2012 (the latter only surviving after massive downsizing whilst Ilford was rescued by a management buyout).

Kodak (which was under bankruptcy protection from January 2012 to September 2013) and other companies have noticed this upward trend: Dennis Olbrich, President of the Imaging Paper, Photo Chemicals and Film division at Kodak Alaris, has stated that sales of their photographic films have been growing over the past three or four years.

[61] In 2023, a Finnish chemist Sami Vuori invented a reusable film that uses synthetic hackmanite (Na8Al6Si6O24(Cl,S)2) as the photosensitive medium.

Visible light bleaches the hackmanite particles back to white, which gives rise to the formation of a positive image.

If the user wants to spare the image, the film can be put into a dark place, as the bleaching process stops completely in the absence of light.

[62] Another reusable film invented by Liou et al. is based on 9-methylacridinium-intercalated clay particles, but erasing the image requires dipping the material in sulfuric acid.