Photographic film
Photograph by nlannon Flickr.
It is removed from the film in the fix step. film Color print film generally has greater exposure latitude than other Photographic film types of film.
This allows a light meter to be used to estimate an exposure. Professional photographers of static subjects such as portraits or landscapes Horror film usually seek these qualities, and therefore require a tripod to stabilize the camera for a longer exposure.
The earliest lenses needed Photographic film to focus blue light only. Following development, the silver is converted back to silver salts in the bleach step.
Typically the blue-sensitive layer is on top, followed by the green and red layers. Infrared films may be shot in standard cameras using an infrared band- or long-pass filter, Photographic film although the infrared focal point must be compensated for. Exposure and focusing are difficult when using UV or IR film with a camera and lens designed for visible light.
The amount of exposure variation that a given film can tolerate while still producing an acceptable level of quality is called its exposure latitude. The international standard for rating film speed is the ISO scale which combines both the ASA speed and the DIN speed in the format ASA/DIN.
A dark image on the negative is of higher density than a more transparent image. Most films are affected by the physics of silver grain activation (which sets a minimum amount of light required to expose a single grain) and by the statistics of random grain activation by photons. A red window could be used to view frame numbers of rollfilm; any red light which leaked beyond the film backing would not fog the film; and red lighting could be used in darkrooms.
Using ISO convention film with an ASA speed of 400 would be labeled 400/27°. Divide the long number by 16 and record the number before the decimal, then multiply the number after the decimal by 16, this could give you a result such as 18 and 2. The first number is known as the PRODUCT (film manufacturer) and the second number as the MULTIPLIER (speed of the film ISO).
A simple, idealized statistical model yields the equation density = 1 - ( 1 - k ) ^ light, where light is proportional to the number of photons hitting a unit area of film, k is the probability of a single photon striking a grain (based on the size of the grains and how closely spaced they are), and density is the proportion of grains that where hit by at least one photon. If parts of the image are exposed heavily enough to approach the maximum density possible for a print film, then they will begin losing the ability to show tonal variations in the final print. Apochromatic lenses are sometimes recommended due to their improved focusing across the spectrum. Film optimized for sensing X-ray radiation is commonly used for medical imaging by placing the subject between the film and a source of X-rays, without a lens, as if a translucent object were imaged by being placed between a light source and standard film. Film optimized for sensing X-rays and for gamma rays is sometimes used for radiation dosimetry and personal monitoring. Film has a number of disadvantages as a scientific detector: it is difficult to calibrate for photometry, it is not re-usable, it requires careful handling (including temperature and humidity control) for best calibration, and the film must physically be returned to the laboratory and processed.
Additionally, because print film must be printed to be viewed, after-the-fact corrections for imperfect exposure are possible during the printing process. The concentration of dyes or silver salts remaining on the film after development is referred to as optical density, or simply density; the optical density is proportional to the logarithm of the optical transmission coefficient of the developed film. Dyes, which adsorb to the surface of the silver salts, make the crystals sensitive to different colors.
e.g. Photographic film is a sheet of plastic (polyester, nitrocellulose or cellulose acetate) coated with an emulsion containing light-sensitive silver halide salts (bonded by gelatin) with variable crystal sizes that determine the sensitivity, contrast and resolution of the film.
Beginning in the 1920s, nitrate film was replaced with cellulose acetate or safety film . Photographing subjects such as rapidly moving sports or in low-light conditions, a professional will choose a faster film.
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). A fourth naming standard is GOST, developed by the Russian standards authority.
The film requires a minimum amount of light before it begins to expose, and then responds by progressive darkening over a wide dynamic range of exposure until all of the grains are exposed and the film achieves (after development) its maximum optical density. Over the active dynamic range of most films, the density of the developed film is proportional to the logarithm of the total amount of light to which the film was exposed, so the transmission coefficient of the developed film is proportional to a power of the reciprocal of the brightness of the original exposure. When the exposed grains are developed, the silver salts are converted to metallic silver, which block light and appear as the black part of the film negative. Color film uses at least three layers.
The first transparent plastic film was produced in 1889. This original film was coated on paper.
For example, Agfa 10E56 holographic film has a resolution of over 4,000 lines/mm—equivalent to a pixel size of 0.125 micrometres—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 micrometres and a dynamic range of 3-4 orders of magnitude. Special films are used for the long exposures required by astrophotography. Film manufacturers commonly make film that is branded by other companies. This changeover was not completed until 1933 for X-ray films (where its flammability hazard was most acute) and for motion picture film until 1951. Early photographic plates and films were sensitive to blue light only.
Orthochromatic film sensitive to the spectral range from green to blue was introduced in 1879 and was dominant until the mid-1920s, when panchromatic film sensitive to the entire visual spectrum became standard. But in a color film, the by-products of the development reaction simultaneously combine with chemicals known as color couplers that are included either in the film itself or in the developer solution to form colored dyes.
The benefit of slower film is that it usually has finer grain and better color rendition than fast film. Eastman Kodak developed the first flexible photographic film in 1885.
See instant film. Films can be made to record non-visible ultraviolet (UV) and infrared (IR) radiation. The focal point for IR is slightly farther away from the camera than visible light, and UV slightly closer; this must be compensated for when focusing.
During development, the exposed silver salts are converted to metallic silver, just as with black and white film. This leaves behind only the formed color dyes, which combine to make up the colored visible image. Newer color films, like Kodacolor II, have as many as 12 emulsion layers, with upwards of 20 different chemicals in each layer. Due to film photography s long history of widespread use, there are now around one trillion pictures on photographic film or photographic paper in the world, There are two primary types of photographic film: In order to produce a usable image, the film needs to be exposed properly.
Some photographers use their knowledge of these limits to determine the optimum exposure for a photograph; for one example, see the Zone system. Their work enabled the first quantitative measure of film speed to be devised. Early photography in the form of daguerreotypes did not use film at all.
Modern films have bar codes (DX codes) on the edge of the film which can be read by a bar code reader. This procedure is usually only performed by photographers who do their own development or professional-level photofinishers.
The ISO standard for film speed only applies to visible light, so visual-spectrum light meters are nearly useless. This is due to the statistics of grain activation: as the film becomes progressively more exposed, each incident photon is less likely to impact a still-unexposed grain, yielding the logarithmic behavior.
Grain size refers to the size of the silver crystals in the emulsion. See the film speed article for a table of conversions between ASA, DIN, and GOST film speeds. Common film speeds include ISO 25, 50, 64, 100, 160, 200, 400, 800, 1600, and 3200.
After World War II, much progress was made, and color became used for the overwhelming majority of photographs. Photographic lenses and equipment are designed around the film to be used. Some subject matter is tolerant of very heavy exposure; brilliant light sources like a bright lightbulb, or the sun, included in the image generally appear best as a featureless white on the print. Likewise, if part of an image receives less than the beginning threshold level of exposure, which depends upon the film s sensitivity to light—or speed—the film there will have no appreciable image density, and will appear on the print as a featureless black.
Before this, glass photographic plates were used, which were far more expensive and cumbersome, albeit also of better quality. Because the by-products are created in direct proportion to the amount of exposure and development, the dye clouds formed are also in proportion to the exposure and development.
More rarely, a film can be pulled to behave like a slower film. Hurter and Driffield began pioneering work on the light sensitivity of film in 1876 onwards. ISO 25 film is very slow , as it requires much more exposure to produce a usable image than fast ISO 800 film.
More highly corrected lenses for newer emulsions could be used with older emulsion types, but the converse was not true. The filters used were different for the different film types. The progression of lens design for later emulsions is of practical importance when considering the use of old lenses, still often used on large-format equipment; a lens designed for orthochromatic film may have visible defects with a color emulsion; a lens for panchromatic film will be better but not as good as later designs. While color processing is more complex and temperature-sensitive than for monochromatic film, the great popularity of color and almost disappearance of monochrome prompted the design of monochromatic film which is processed in exactly the same way as a standard color film. Instant photography, as popularised by Polaroid, uses a special type of camera and film that automates and integrates development, without the need of further equipment or chemicals. This is because film is sometimes processed differently according to specifications of the film, determined by its manufacturer; the bar code is entered into the computer printer before the film is printed. To establish the OEM, read the bar code printed on the cassette.
Most automatic cameras instead try to achieve a particular average density. Film speed describes a film s threshold sensitivity to light. All of these films were used to produce black-and-white images, regardless of spectral sensitivity. Experiments with color photography were first made in 1861, but generally usable color films only became available in the 1930s.
Chemical processes can then be applied to the film to create a visible image, in a process called film developing. In black-and-white photographic film there is usually one layer of silver salts. These films generally require special equipment; for example, most photographic lenses are made of glass and will therefore filter out most ultraviolet light.
Hermann Wilhelm Vogel discovered that the spectral sensitivity could be extended by dye sensitization. The introduction of orthochromatic film required the spectrum from green to blue to be brought to the same focus.
This was no longer acceptable with the introduction of color film. With the introduction of panchromatic film the whole visual spectrum needed to be brought to the same focus.
Usually those areas will be deemed to be overexposed and will appear as featureless white on the print. In order to do this, the film must be developed for a longer amount of time or at a higher temperature than usual.
The first photographic film was made from highly flammable nitrocellulose with camphor as a plasticizer (celluloid). Film manufacturers can supply suggested equivalent film speeds under different conditions, and recommend heavy bracketing.
This process is carried out immediately after exposure, as opposed to regular film, which is developed afterwards and requires additional chemicals. The smaller the crystals, the finer the detail in the photo and the slower the film. A film with a particular ISO rating can be pushed to behave like a film with a higher ISO.
In the previous example, 18 identifies 3M as the manufacturer and 2 means it is 200 ISO: . Some films, like Kodak s Technical Pan, are not ISO rated and therefore careful examination of the film s properties must be made by the photographer before exposure and development.
Instead, expensive lenses made of quartz must be used. In all cases a color cast in the lens glass or faint colored reflections in the image were of no consequence as they would merely change the contrast a little.
When the emulsion is sufficiently exposed to light (or other forms of electromagnetic radiation such as X-rays), it forms a latent (invisible) image. Against this, photographic film can be made with a higher spatial resolution than any other type of imaging detector, and, because of its logarithmic response to light, has a wider dynamic range than most digital detectors.
