# Film speed

As film speed (English film speed ) is called the light sensitivity of photographic plates and films . If the light sensitivity is higher, you can take pictures in a darker environment with the same exposure time or you have to reduce the exposure time with the same brightness.

Kodak TX 120 from 1975

The film speed is indicated today in ISO and partly for comparison purposes also in DIN , ASA or GOST ; In the past, specifications were in Weston , General Electric (GE) , American or European Scheiner grades, H&D grades and various other systems.

DX coding on a film cartridge

The specification of the film speed can be found on the film packaging and on the film cartridge . The cartridges of 35mm films in format 135 have been provided with the automatically readable DX coding since 1983 , which consists of a checkerboard pattern (CAS code) made of conductive material that can be read by the camera and a barcode that can be read by the film processing machines in the laboratory . In addition to other information, the nominal sensitivity of the film is also listed there. The cartridges for APS films in the IX240 format (aka Advantix), introduced in 1996, also contain DX-iX code information. Since around 1998 a similar system has also been available for roll films in formats 120 and 220, which was introduced by Fujifilm under the name “Barcode System”. It is u. a. the film sensitivity is coded in the context of a barcode on the sticker that connects the light-sensitive film with the carrier paper. This barcode can be read by some newer medium format cameras.

The sensitivity specifications of digital cameras with image sensors are made by specifying an exposure index and are based on the definitions for films.

## Film speed rating

All film speed specifications are based on steps at a distance of 1/3 f-stop, but the numerical dimensions are scaled differently: logarithmically for DIN, linear for all others. The dimensions correspond to a sensitivity guide value Sv (English speed value / sensitivity ) in exposure levels according to the APEX system .

### Current system

#### ISO

The standard of the International Organization for Standardization (ISO) combines the numerical values ​​according to ASA PH2.5-1960 and DIN 4512: 1961-10 from 1974 . This results in, for example, a film speed specification such as ISO 100/21 °, in which the first-mentioned so-called linear ISO value corresponds to the linear ASA value (in its meaning from 1960) and the so-called logarithmic ISO value corresponds to the DIN degrees (in their use from 1961). In practice, the logarithmic ISO value is often left out. B. a specification like ISO 100 actually for ISO 100/21 °. An indication such as B. ISO 21 ° is acceptable.

The specification for black and white negative films can be found in the ISO 6 standard of February 1993 (1st edition 1974) and for color negative films for still photography in ISO 5800 of November 1987 (1st edition 1979); this edition received a small correction in June 2001. The determination of the ISO speed of color reversal films is standardized in ISO 2240 from October 2003 (2nd edition 1982, 3rd edition 1994).

The specification of the film speed in ISO became widespread in Japanese cameras from around 1982. Initially, the cameras still had a combination label "ASA / ISO" instead of the previously common "ASA" scaling, but from around 1985 film speed on camera housings became practical only labeled with "ISO".

ISO specifications common today on films and digital cameras are:

25 50 64 100 200 400 800 1600 3200 6400 12800 25600 51200 102400 204800 409600 …


Values ​​in italics are less common, the values ​​highlighted in bold represent the standard. The five- and six-digit values ​​are now found in digital cameras. The higher the number, the less light is required when taking photos, thus the necessary exposure time is reduced - the photographer then speaks of a “fast film”. It should be noted, however, that the higher the film speed, the less the image information. This becomes apparent in the photograph through coarser film grain , which can also be a desired stylistic device , especially in black and white photography , or as undesirable image noise and a lower dynamic range in digital photography.

### Older systems

#### DIN

In January 1934 by the German Institute for Standardization e. V. introduced DIN standard DIN 4512 , a possibility for specifying film sensitivities - called "light sensitivity" at the time - for black and white negative films was presented. This standard also describes the exact procedure for determining the respective sensitivity.

The film speeds in degrees DIN were given with a numerical value and a number, for example 21 ° DIN for a film with a sensitivity of (today) ISO 100/21 °. Until the revision of the DIN standard in November 1957, a slightly different tenth of a degree fractional spelling in the form 21/10 ° was still common. Specifications in DIN are scaled logarithmically to ten; a difference of 3 ° DIN therefore practically corresponds to a doubling of the sensitivity (as with decibels ); a film with 24 ° DIN is twice as sensitive as one with 21 ° DIN. A difference of 20 ° DIN corresponds to a hundredfold increase in sensitivity.

The DIN standard was inspired by Julius Scheiner's system of Scheiner degrees from 1894, although there is still a difference of 19 ° Sch. was accompanied by a hundredfold increase in sensitivity (and thus a difference of 3 ° Sch. was only approximately doubled):

“The sensitivity measurement in the DIN system is based on the exposure of the materials through a stepped gray wedge with a constant which is such that three times the logarithm of two is equal to two. So this constant is a good approximation of 0.1. The first zone under the gray wedge, the density of which differs by at least 0.1 from the unexposed material after the material has been developed, determines its sensitivity. The exposure takes place with a standardized light, which is characterized by a certain approximation of the spectral composition of daylight, which was not the case with the Scheiner system. The exposure time is determined by a gravity shutter. "
${\ displaystyle \ log _ {10} (2) = 0 {,} 301 \ dots \ approx 3/10}$

The criticism of the sensitivity determination according to DIN that negatives would come too steeply so that the nominal sensitivity could not be exploited was only moderated with the revisions of DIN 4512 in 1957 and 1961.

As part of the new version of DIN 4512 in 1961, the assignment of film speeds to the then new ASA standard ASA PH2.5-1960 from the previous year was also overtaken. The DIN grades were now - like the ASA numbers before - usually increased by a whole exposure level, i.e. H. a black and white negative film, which was previously specified with 21 ° DIN, now got a nominal sensitivity of 24 ° DIN without changing the emulsion. In some cases, the film and photo industry followed with a delay, which caused considerable confusion among users for several years. Strictly speaking, it is only from this point in time that the equivalent of 12 ° DIN = 12 ASA = ISO 12/12 °, 21 ° DIN = 100 ASA = ISO 100/21 ° and 30 ° DIN = 800 ASA, which can still be found in the ISO standard today, applies = ISO 800/30 °. From 1961 the degree symbol should be omitted when specifying DIN degrees, example: 21 DIN instead of the previous 21 ° DIN; However, this has only partially prevailed, since the later logarithmic ISO values ​​are still written with degree symbols to make them easier to distinguish.

The DIN method for determining the sensitivity was initially only applicable for black and white negative films, but not for color negative films and color or black and white reversal films. So that users could still work with the common exposure meters, the manufacturers of such materials, assuming motifs with an average luminance distribution, made their own recommendations for “to expose like ... DIN”. In the course of the further development of this standard, the content was greatly expanded and reorganized into the nine parts 1 and 3 to 10: DIN 4512-1: 1971-04 concerned black and white negative films ; its last edition DIN 4512-1: 1993-05 was replaced by DIN ISO 6: 1996-02 in September 2000 . DIN 4512-4: 1977-06 treated color reversal films; the last edition of DIN 4512-4: 1985-08 was replaced by DIN ISO 2240: 1998-06 in July 2002 . DIN 4512-5: 1977-10 treated color negative films ; the last edition of DIN 4512-5: 1990-11 was also replaced in July 2002 by DIN ISO 5800: 1998-06 .

#### ASA

ASA (American Standards Association) was the name of the American National Standards Institute ( ANSI ) from 1928 to 1966 . An ASA standard from the 1940s defined procedures for determining the sensitivity of black and white negative films.

This ASA film speed has a linear division, that is, a film with 200 ASA is twice as sensitive as a film with 100 ASA; thus - apart from the Schwarzschild effect - it results in an equally exposed image with half the exposure time or with exposure with a whole f-stop less.

The ASA standard was heavily revised in 1960; With the ASA PH2.5-1960 , there were sometimes serious deviations in which, due to the omission of a safety factor, the sensitivity specifications of black and white films were usually increased by a whole exposure level, which led to such films with z. B. A sensitivity of previously 100 ASA ("old ASA") without changes to the emulsion now corresponded to 200 ASA ("new ASA"). Older ASA information can therefore only be compared with the later values ​​to a limited extent. The new version of DIN 4512: 1961-10 that followed a year later carried out a similar development. The film sensitivities in "BS" defined in the British standard BS 1380 from 1963 also correspond to the ASA PH2.5-1960 and must not be confused with an older system with information in BSI that was used in England and which corresponded to the European Scheiner grades. The ASA standard was replaced in 1987 by ISO 5800, which continues the use of linear ASA values ​​(in their meaning from 1960) as linear ISO values ​​until today. The last edition of BS 1380 was divided into 8 parts; the parts of the standard dealing with film speed were later replaced by national implementation of the ISO standards: BS ISO 6 for black and white negative film , BS ISO 2240 for color reversal film and BS ISO 5800 for color negative film. Particularly noteworthy is BS 1380-5 from 1985 "Speed ​​of sensitized photographic materials - Method for determining the speed of direct positive color print camera materials", which was replaced in 1996 by BS ISO 7187 ; thus the second edition of ISO 7187 was implemented nationally in Great Britain. The standard concerns materials for color printing cameras.

In addition to the already established linear ASA value, logarithmic ASA grades were also introduced as part of the ASA PH2.5-1960 (notation: 100 ASA = 5 ° ASA), in which a difference of 1 ° ASA corresponded to a whole exposure level and thus each doubled the film speed. ASA grades were e.g. Some of them are also printed on film packaging and are still in use today as a sensitivity guide value Sv within the framework of the APEX system.

The last edition of this standard dates from 1979. It bears the number ANSI PH2.5 and the title "Speed ​​of photographic negative materials (monochrome, continuous tone), method for determining". It was replaced in 1986 by the American standard NAPM IT2.5 , which is a national implementation of the international standard ISO 6 . The last edition of NAPM IT2.5 is from 1993. NAPM is the abbreviation for National Association of Photographic Manufacturers Incorporated.

#### GOST

For older Russian cameras, the film speed is specified in GOST (Cyrillic: ГОСТ) according to the GOST standard . A distinction must be made between the old GOST 2817-50 standard , which was valid from October 1951 to December 31, 1986 and replaced the Hurter & Driffield sensitivities used since 1928 , and the amended GOST 10691-84 standard , which was introduced in the USSR was valid on January 1, 1987. With the amended version, the national standard of the old GOST was abandoned. The new GOST introduced the international measurement method of ISO in the Soviet Union and its successor states . When GOST is mentioned in photo technology, the old GOST is usually meant. Their values ​​roughly correspond to those of the ASA, but are somewhat lower due to a different derivation:

• 90 GOST are 100 ASA,
• 180 GOST are 200 ASA, etc.

### Historical systems

In the explanations for DIN 4512 from January 1934, the oldest sensitivity specification mentioned is one according to Leon Warnerke ( Władysław Małachowski ) from 1880, the unreliability of which soon became apparent, but was later further developed by Henry Chapman Jones .

Several new methods were developed around 1890-1900, including: a. Sensitivity data for plates according to George Frederick Wynne (Plate Speed ​​Numbers), Alfred Watkins (Exposure Speeds) and Dr. John Henry Smith for use with their light meters. The rather complex process of the English company Hurter & Driffield ( H&D Speed ​​Numbers) from 1890, whose weaknesses became apparent with the appearance of sensitized layers, was also widespread .

Information in units of measurement according to US or European Scheiner degrees , Henry Solomon Wellcome (Wellcome exposure computer 1900–1950), Eder-Hecht , BSI , Amateur Photographer (AP) , Compass ( Compass Units , CU ), Ilford Speed ​​Groups , Philip Smethurst , Weston , General Electric (GE) or Loyd Ancile Jones / Kodak are also older methods for determining film speed that are no longer in use today.

Optical light meter with DIN, Scheiner and H & D degrees; the exposure meter has a ring with numbers of different brightness, the number that can just be made out corresponds to the brightness.

One of the oldest known systems for specifying the sensitivity of photographic materials comes from the astronomer Julius Scheiner (1858–1913), who first specified his information in 1894.

“Scheiner rotated an opaque disk at a certain speed, from which an opening had been sawn out in the shape of 20 concentric sector rings, the sector angles of which formed an increasing geometric sequence from the outside to the inside. The constant of the geometric sequence was chosen so that the last angle was 100 times larger than the first. The constant thus corresponded to the nineteenth root of 100, i.e. approximately 1.274 ... A standardized light source illuminated the disk from a very specific distance. A cassette was attached behind the pane [...] which held the material to be tested. This cassette was opened for exactly one minute while the disc rotated. The number of the first ring, counting from the inside out, behind which the material had a minimal, precisely defined blackening after development, determined the degree of sensitivity in Scheiner degrees of the material to be tested. The last grade on this scale (which was later to be expanded to include higher levels of sensitivity), grade 20, corresponded to 100 times greater sensitivity than the first. A difference of 3º Scheiner corresponds approximately to double the sensitivity, since the third power of the nineteenth root of 100, namely 2.069 ..., is an approximation of the number 2. "
${\ displaystyle {\ sqrt [{19}] {100}} ^ {3} = 2 {,} 069 \ dots \ approx 2}$

Originally intended for astronomical purposes and initially limited to 20 °, the Scheiner method, which is widely used in the German-speaking world, was later improved by Josef Maria Eder . The explanations for DIN 4512 from 1934, which are intended to justify the introduction of the standardized procedure, say :

“Here, too, it turned out after some time that the measurement method, despite the changes made by Eder, was not able to fully take into account the requirements of practice, so that every manufacturer […] had to determine the sensitivity in degrees of Scheiner according to his own system, often very much primitive way by […] comparison with products from other manufacturers. The practical apparent degrees determined in this way no longer have anything to do with the originally worked out measuring method according to Scheiner. [...] As a result, there has gradually been inflation in degrees of sensitivity for which Scheiner's method is nothing more than the name. "

16 ° (European) lights correspond to ISO 3/6 °, 19 ° (European) lights correspond to ISO 6/9 °.

#### Weston Film Speed ​​Ratings

The Weston Film Speed ​​Ratings date from the 1930s, a time when the ASA standard did not yet exist; they were from the same manufacturer Edward Weston of light meters introduced and continued (Model II production at the end of the exposure meter) to 1956th As a rule of thumb, data from ASA (until 1960) can be converted to Weston by subtracting 1/3 f-stop from the ASA value; 125 ASA ("old ASA") become 100 Weston. Weston light meters from 1956 (model III) adopted the ASA scaling.

#### General Electric (GE)

General Electric (GE) information was in use in the 1940s and 1950s. As a rule of thumb, you can convert data from ASA (until 1960) to GE by adding 1/3 f-stop to the ASA value; 100 ASA ("old ASA") become 125 GE.

## Differentiation areas

Photographic recording materials are available in different film speeds. Today you get photographic films with sensitivities between about ISO 25/15 ° (low- sensitive film) and ISO 3200/36 ° (highest-sensitive film) .

A more sensitive film enables hands-free photography in low light, longer flash ranges and shorter exposure times. The graininess increases with the sensitivity, so the structure of the grain becomes visible even with low enlargements of negatives of sensitive films . The sharpness and resolution are also better with low-sensitivity films.

These assignments are dependent on technical developments and are therefore relative; Film speed ratings for a "high speed" film are not absolute classifications. As "normal sensitivity" has been designated, for example, a material the early 20th century, the DIN ° (2.5 ASA) film had a sensitivity of about 5 as the Agfa Color - color film 1936; the Kodachrome from the same year already showed 10 ASA and was therefore - for a color film - highly sensitive. The 1942 Kodacolor® process had sensational sensitivity at 20 ASA. The following assignments therefore relate to the current classification (as of 2004).

### Low sensitivity films

Low-sensitivity films offer the highest sharpness and the finest graininess. They are therefore particularly suitable for slide projections , the production of prints in poster size as well as photography in high brightness with an open aperture and a bright lens.

The low- sensitivity specialty films include orthochromatic and panchromatic document films , low- sensitivity halftone films and aerial films , as well as black and white reversal films and infrared films .

### Normal sensitivity films

Films of medium sensitivity (100/21 ° and increasingly ISO 200/24 ​​°) are sold most frequently today . This also includes half-tone films with normal sensitivity and chromogenic films .

### High sensitivity films

Highly sensitive films are particularly suitable for sports photography and photography with telephoto lenses . Ansco presented the first color film that was highly sensitive or, by the standards of the time, the highest sensitivity in 1967 with the Anscochrome slide film and a sensitivity of 500 ASA.

• ISO 400/27 ° (resolution about 100-150 lines / mm): For example Kodak Tri-X , Kodak Tmax 400 , Ilford Delta 400 , Ilford HP5 , Ilford Delta 400, Fuji Neopan Professional 400 (black and white film), Orwo N74 , Fuji Provia 400 F (professional film), Fuji Superia X-TRA 400 (consumer film), Ilford XP2 Super 400 (monochromatic film), Kodak color world 400 (consumer film), Kodak Elitechrome 200 (slide film)
• ISO 800/30 °: For example Fuji Superia X-TRA 800, Kodak Portra 800 (portrait film)

### Highly sensitive films

Highly sensitive films are particularly suitable for available light and theater photography . Highly sensitive consumer slide films are no longer available, in this segment there are only negative films with up to ISO 1600/33 °

• ISO 1600/33 °: For example Fuji New Superia 1600 (consumer film), Fuji Neopan 1600 ( b / w film)
• ISO 3200/36 °: Ilford Delta 3200 (SW) (*), Kodak Tmax P3200 (SW)
• ISO 6400/39 °: Kodak Ektapress 6400 (discontinued)

(*) According to the manufacturer's data sheet, the Ilford Delta 3200 Professional has a nominal sensitivity of ISO 1000/31 ° determined in accordance with the ISO standard. Nevertheless, the manufacturer recommends setting the exposure meter as if the film had an ISO nominal sensitivity of ISO 3200/36 °. The specification 3200 in the product name here corresponds to the EI value (EI = Exposure Index), which is 3200/36.

## History and Development

The first photographic emulsions from the 1850s ( wet collodion process ) still had a very low sensitivity to light; the exposure times were mostly in the range from a few seconds to minutes. For comparison: The first photographs ever took another eight hours. This value was improved by a factor of about 100 with the gelatine drying plate of 1871; the dry plate process achieved a sensitivity of about 5 ASA.

From the end of the 19th century, the light sensitivity was standardized, the first measured variable was the shimmer degree ; thereafter various other processes were developed by General Electric (GE), Weston and GOST , but today only information in ASA and DIN and, since 1979, in ISO are used.

The black and white roll films of the 1920s had - converted from the old Scheiner degrees - a sensitivity of around ISO 16/13 °. The Agfa Isochrom brought an improvement, reaching ISO 32/16 ° in 1932 and ISO 50/18 ° in 1934. The Kodak Panatomic from 1939 with ISO 64/19 °, the Voigtlander Bessapan with ISO 100/21 ° and finally the Gevaert Gevapan from 1952 with ISO 160/23 ° were even more sensitive .

The first color films, such as the Agfacolor® color film from 1936, had a sensitivity of ISO 2.5 / 5 °. The contemporary Kodachrome already had ISO 10/11 ° and was therefore highly sensitive for a color film of the time. The Kodacolor process from 1942 had a sensational sensitivity with ISO 20/14 °. In the 1950s, the typical black and white recording material for box cameras had a sensitivity of ISO 40/17 °.

Ansco presented the first high-speed or, by the standards of the time, highly sensitive film in 1967 with the Anscochrome slide film and a film speed of ISO 400/27 °. Other highly sensitive color negative films with ISO 400/27 ° appeared on the market in 1977 ( Fujicolor II 400 , Kodacolor 400 ). Corresponding reversal material followed a year later with the Ektachrome 400.

In 1982 Kodak introduced T-Grain technology based on silver halide crystals and launched the Kodacolor VR-1000, the first high-speed film by today's standards. At the end of the 1980s, Agfa slide films with 1000 ASA appeared, and in 1993 Fuji produced the first color negative film with ISO 800/30 ° ( Fujicolor Super G ).

Films have been DX-coded since 1983 , which means that there is an automatically readable code on the film cartridge which, among other information, also contains the nominal sensitivity of the film.

## properties

The higher the sensitivity, the lower the resolution of the film, as the light-sensitive crystals become larger and larger and can ultimately be seen as a coarse grain in the photo. More sensitive films have poorer color fidelity and a loss in contrast range (compare gradation behavior ). In addition, as sensitivity increases, so does the selling price.

With older cameras, the film speed must be set manually; Modern electronic cameras evaluate the DX coding on the film cartridge, which contains information about the film speed and length.

## Push and pull development

C-41 for black and white film

The speed of a film depends not only on how the film was made, but also somewhat on its development . The information printed on the films are nominal sensitivities that relate to the standardized developments C-41 for color negative films and E-6 for slide films .

Accidentally or intentionally incorrectly exposed films can be developed with a special development and thus provided with in some cases significantly steeper or even flatter gradation curves; this is called overdevelopment ( pushing ) or underdevelopment (pulling). The film speed hardly changes when pushing (only the increase becomes steeper °), while pulling the film speed is lower.

The ability to push and pull films differs depending on the type of film and - especially in the case of consumer films - also on the respective batch. In the case of professional recording material, the push and pull behavior of the respective film is documented in the manufacturer's data sheets , as is the associated gradation curve with modified development parameters .

Color negative films have a fairly large exposure latitude of up to ± three f-stops anyway, so push or pull development is usually not necessary here. Slide films, on the other hand, generally require precise exposure or targeted over- or under-development, but the tolerances are lower (usually ± one f-stop).

For black and white films, a film with ISO 400/27 ° can usually be exposed like ISO 1600/33 ° and developed with a push of two f-stops. However, if the exposure is further reduced in accordance with ISO 3200/36 ° and the development is extended again, a disproportionate increase in the grain size and a haze is to be expected. This is not a real increase in film speed according to the ISO standard, for which the development process, negative contrast and shadow density to be achieved are strictly defined. Push and pull processes consciously vary these parameters and adapt them to the requirements of a recording under requirements that deviate from the norm. During the push process with black and white negative film, shadow areas increasingly lose their markings due to the fact that the actual film sensitivity increases only slightly compared to the greatly reduced exposure. As a result of the increased contrast when the development is extended, a differentiated reproduction of the highlights becomes increasingly difficult or even impossible.

Pulling, just like pushing, only slightly changes the measurable film speed. The film speed characterizes the exposure, which causes a slight blackening of the film material. Pulling and pushing change the gradation, however, so that the normally used exposure range for mids ( D  = + 0.5… 1) shifts accordingly.

## Physical relationships

### Black and white negative film sensitivity

The sensitivity of black and white negative film for still photography is defined in the international standard ISO 6 of February 1996, which was also adopted in Germany as the national DIN ISO 6 edition . The 1st edition of the international ISO 6 was published in 1974. The stipulations do not apply to aerial photography, motion picture photography, graphic, radiological and micrographic applications, and also not to negatives that were created with diffusion transfer systems. Since September 2000, DIN ISO 6 has replaced the purely national standard DIN 4512-1 , May 1993 edition. It is based on DIN 4512 “Negative material for pictorial recordings; Determination of the sensitivity to light ”from January 1934. This introduced the sensitivity in "Degrees DIN (° DIN)".

For this purpose, the blackening is determined depending on the exposure . The ISO sensitivity S for black and white negative film is based on the exposure H m , which leads to an optical density of 0.1 (above the gray haze ) and is calculated from the relationship S = 0.8 lux · s / H m .

A black and white negative film with 1 DIN / ASA has one exposure

• of 0.8 lux · s an optical density of D = + 0.1 above the gray haze and
• of 16 lux · s an optical density of D = + 0.9 above the gray haze.

The development of the film is to be adjusted in such a way that a gamma value of the gradation of about 0.61 to 0.62 is established (d D  = 0.8; log H / H m  = 1.3). When exposing films with different sensitivities, the required exposure time is reduced in inverse proportion.

An exposure whose geometric mean value of the brightness is H g  = 11.38 * H m is regarded as a standard exposure . This corresponds to an exposure of 9.1 lux · s for a sensitivity of 1 DIN.

Since the standardized development process has too much contrast for many requirements, the effective DIN value is often corrected to the requirements for image contrast (e.g. using the zone system).

### Color negative film sensitivity

The sensitivity of the color negative film is defined in ISO 5800 .

For this purpose, the optical density is determined separately for all 3 colors depending on the exposure .

The ISO sensitivity S for color negative film is based on the exposure H m , which leads to an optical density of 0.1 (above the gray haze ) and is calculated using the relationship S = 1.414 lux · s / H m . In contrast to black and white negative film, development is not defined by two points, but refers to the standard development process intended for the film (usually C-41 ).

An exposure whose geometric mean value of the brightness is H g  = 6.43 * H m is regarded as a standard exposure . This corresponds to an exposure of 9.1 lux · s for a sensitivity of 1 DIN.

### Color slide film sensitivity

The sensitivity of the color slide film (also called color reversal film) is defined in the international standard ISO 2240 from October 2003; this edition was adopted in October 2005 as DIN ISO 2240 in the German set of standards. The specifications also apply to 8 mm and 16 mm motion picture films, but only for non-professional applications.

For this purpose, the optical density is determined depending on the exposure . The ISO sensitivity S for color slide film is based on the exposure H m , which leads to an optical density of 1.0 (above the gray haze ) and is calculated using the relationship S = 10.0 lux · s / H m .

In contrast to the black and white negative film, the development is not defined by two points, but relates to the standard development process that is intended for the film (mostly E-6 , with Kodachrome K-14 ).

An exposure whose geometric mean value of the brightness is H g  = 0.91 * H m is regarded as a standard exposure . This corresponds to an exposure of 9.1 lux · s for a sensitivity of 1 DIN.

### Sensitivity in semiconductor sensors

CCD - and CMOS - sensors of digital cameras , which are based on the internal photoelectric effect, not can be characterized with the methods of the chemical film. On the one hand, they have no optical density; on the other hand, it is not possible to match the strictly linear characteristics of semiconductor sensors to the gradation curves of film material. The characterization must therefore be carried out on the basis of the electrical or the digitized output signal of the sensor.

In this way, a film sensitivity analogous to that of a chemical film can also be defined for semiconductor sensors. The sensors can be set to a lower or higher sensitivity via the camera electronics using software parameters. Similar to the chemical film, the noise can be reduced when the sensitivity is set to low; setting a higher sensitivity, on the other hand, usually leads to an increase in image noise. Higher sensitivities are achieved by amplifying the (analog) signal of the sensor more strongly before digitization .

 ISO 100 ISO 200 ISO 400 ISO 800 ISO 1600 ISO 3200 Examples of the effect of the ISO setting on a digital SLR camera ( Konica Minolta Dynax 7D ) with APS-C size CCD sensor .

With digital sensors, depending on the application, the sensitivity is defined either in relation to the degree of saturation of the sensor with a lot of light, in relation to the signal-to-noise ratio (SNR) or simply on the basis of manufacturer recommendations ( ISO 12232 , Photography - Electronic Still Picture Cameras - Determination of ISO Speed).

The camera electronics or the RAW converter are calibrated using the desired ISO value so that the digitally encoded exposure is converted into a pixel value that represents the actual remission of the object in the color space used (on average approx. 18 percent). The green or yellow channel is used as a reference, as these are the most sensitive.

There are several problems when defining the sensitivity of semiconductor sensors (including the analog-to-digital converter):

• Many semiconductor sensors have a switchable preamplifier, which leads to different sensitivities.
• Semiconductor sensors are too broadband for normal photography, so that blocking filters are used, which reduce the sensitivity by a factor of 2 to 2.5. In practice, the sensitivity of the sensor + blocking filter is measured in this case.
• There are different definitions for the sensitivity, saturation-based and SNR-based, the latter additionally with different additional parameters.
• A semiconductor sensor, in combination with the camera electronics, is so flexible that the whole concept of standardized film sensitivity can be questioned. This knowledge has also led to the definition of more or less arbitrary ISO values ​​by the camera manufacturer.

#### Saturation-based sensitivity

The saturation-based sensitivity S s (based on ISO value) is based on the measurement of the saturation exposure H s . With cumulative sensors, this is a comparatively easily determinable variable. At some point the charge-collecting pixels are so full that the resulting voltage (U = Q / C) is so high that the electrons can leave the pixels. The collected charge (full well capacity) and the associated exposure (in lux · s) can be measured.

The saturation-based sensitivity is defined by S s  = 78 lux · s / H s .

In contrast to chemical film, you cannot directly specify a mean color or density value for a digital sensor. Therefore, H m is set in relation to that exposure at which the sensor or the A / D converter goes into saturation. A common value here is 18/106 if an 18 percent gray card is used as the reference object and a 6 percent safety reserve is planned for saturation. Professional devices allow for a reserve of up to 80 percent here and therefore specify the basic ISO value much more carefully than consumer devices.

With a calibration reference of 18/106 of the maximum saturation, the reserve of a commercially available digital sensor up to saturation is log 2 (106/18) + 0.3 = 2.9 f-stops above the measured value, since a digital sensor is proportional to the change in exposure saturates. This is slightly more than with color reversal film, but less than with negative film. In the other direction there is by definition a reserve of at least −2.5 f-stops, the actual sensitivity limit depends on the signal-to-noise ratio of the sensor.

The saturation-based sensitivity is based solely on the saturation limit of a sensor. It correlates well with the minimum possible sensitivity of a semiconductor sensor, but says nothing about the signal quality in low light. If the storage capacity of the pixels is increased with otherwise the same properties, the saturation-based sensitivity is reduced, although this does not make the sensor less sensitive.

The DXOMark website, which provides extensive readings from sensors on current digital cameras, defines sensitivity as S = 110 lux · s / H s . This is synonymous with the fact that a sensor has to clip from around 220% of the white value . However, many current cameras now have more reserve upwards (to avoid eroded lights), which is chalked up on the DXOMark website as an incorrectly specified ISO sensitivity.

#### SNR-based sensitivity

Signal-to-Noise Ratio (SNR) based ISO sensitivities give a better idea of ​​the signal quality in low light. The ISO sensitivity S depends on the respective measurement specification:

S 10 = 10 / H 10 is the sensitivity at which, with an exposure of H 10, an image that is just acceptable (SNR value of 10) is achieved.

S 40 = 10 / H 40 is the sensitivity at which the first excellent image (SNR value of 40) is achieved with an exposure of H 40 .

The SNR and the saturation reserve (= dynamic range) determine the quality of the sensor: high-quality sensors show details in the shadows and in the lights, while simpler sensors only deliver pure black or white. The SNR data of the sensors used in digital cameras therefore rarely leave the manufacturers' laboratories.

#### Recommended Exposure Index (REI)

Recommended Exposure Index indicates the recommended value for the ISO film speed S of the sensor. This definition has been used for consumer digital cameras since 2004 and is based on the knowledge of the Japanese Camera & Imaging Products Association (CIPA) that complex, standardized measurement methods according to ISO 12232 make little sense for consumer devices where the image is mostly from the image processor in the camera " nicely calculated " (CIPA DC-004 - Sensitivity of digital cameras) .

The REI is defined using the following formula: S REI = 10 / H m . Here, H m is the average exposure of the sensor plane recommended by the manufacturer. There are no specific measuring regulations here; it is assumed that the manufacturers themselves know best how the camera takes the best pictures for the average consumer.

### Film speed and exposure

The illuminance on the film or sensor can be determined by measuring the luminance L of a reflecting object in the scene using the following formula:

${\ displaystyle \ mathrm {E} = {\ frac {b \ cdot L} {k ^ {2}}}}$

k stands for the effective f-number of the lens. The factor b = 0.650 results from the physical properties of the lens (lens transmission, vignetting and stray light factor), an object distance of 80 times the focal length and an angle of 12 ° from the lens axis (ISO measurement specification). With a TTL exposure meter, b is approx. 2 percent larger, since the focal length of the lens and the object distance are automatically taken into account during the measurement. Assuming a distant object on the objective axis to simplify the measurement, b = 0.728.

The exposure time t in seconds gives the exposure H of the film or sensor

${\ displaystyle \ mathrm {H} = E \ cdot t = {\ frac {b \ cdot L \ cdot t} {k ^ {2}}}}$

The correct exposure value H b (see also exposure (photography) ) results from the DIN / ASA value of the film speed S according to ANSI / ISO 2720-1974 using the following formula:

${\ displaystyle \ mathrm {H_ {b}} = {\ frac {b \ cdot K} {S}}}$

The factor K is the calibration factor of the light meter and is selected between 10.6 and 13.4 according to ANSI / ISO 2720-1974 . Usually K = 12.5 for Nikon , Canon , Sekonic and K = 14 for Minolta and Pentax . This difference hardly plays a role in practice.

The relation between the exposure H b proposed by the exposure meter and the reference exposure H m specified in the standard is thus obtained via the respective definition of the sensitivity . The differences reflect the different measurement rules for each film type (reference at the base of the density curve or with a defined mean density or saturation)

• The following applies to black and white negative films : (corresponds to +3.3 f-stops above H m )${\ displaystyle H_ {b} = {\ tfrac {b \ cdot K} {\ mathrm {S}}} = {\ tfrac {b \ cdot K} {0.8}} \ cdot H_ {m} = 10 { ,} 16 \ cdot H_ {m}}$
• The following applies to color negative films: (corresponds to +2.5 f-stops above H m )${\ displaystyle H_ {b} = {\ tfrac {b \ cdot K} {\ sqrt {2}}} \ cdot H_ {m} = 5 {,} 75 \ cdot H_ {m}}$
• For color reversal films (saturation-based measurement) the following applies: (corresponds to −0.3 f-stops in relation to H m )${\ displaystyle H_ {b} = {\ tfrac {b \ cdot K} {10}} \ cdot H_ {m} = 0 {,} 81 \ cdot H_ {m}}$

The deviation from the reference value is not due to the "wrong" calibration of the exposure meter, but to the geometry of the scene and the definition of the film speed.

## Conversion of the film speed

Conversion between ISO, DIN, ASA and GOST:

Conversion between ASA and DIN: DIN = 21 ° + 10 ° log (ASA / 100)

Conversion between ASA and GOST: GOST ≈ 0.9 ASA

## literature

General:

• Felix Freier: DuMont Lexicon of Photography. Dumont Literature and Art Verlag, Cologne 1992, ISBN 3-7701-2982-2 .
• Hugo Schöttle: DuMont's Lexicon of Photography. Photo technique, photo art, photo design. DuMont Reise Verlag, Cologne 1978, ISBN 3-7701-0944-9 .
• KaPe Schmidt: Basics of film material exposure : The guide for a perfect film material and digital exposure. Mediabook International, Stein-Bockenheim 2004, ISBN 978-3-937708-01-0 .

Conversion between GOST / ASA / DIN:

• Polytechnic Dictionary. Moskva, Sovetskaya Encyclopedia, 1980.
• Photo amateur. Letter Reference, Moskva, Iskusstvo, 1981.

Norms and standards:

• ISO 6: 1974 , ISO 6: 1993-02 . Photography - Black-and-white pictorial still camera negative film / process systems - Determination of ISO speed . International Organization for Standardization.
• ISO 2240: 1982-07 , ISO 2240: 1994-09 , ISO 2240: 2003-10 . Photography - Color reversal camera films - Determination of ISO speed . International Organization for Standardization.
• ISO 2720: 1974 . General Purpose Photographic Exposure Meters (Photoelectric Type) - Guide to Product Specification . International Organization for Standardization.
• ISO 5800: 1979 , ISO 5800: 1987-11 , ISO 5800: 1987-11 / Cor 1: 2001-06 . Photography - Color negative films for still photography - Determination of ISO speed . International Organization for Standardization.
• ISO 12232: 1998-08 , ISO 12232: 2006-04 , ISO 12232: 2006-10. Photography - Digital still cameras - Determination of exposure index, ISO speed ratings, standard output sensitivity, and recommended exposure index . International Organization for Standardization.
• DIN 4512: 1934-01, DIN 4512: 1957-11 (sheet 1), DIN 4512: 1961-10 (sheet 1). Photographic sensitometry, determination of optical density . German Standards Committee (DNA). Replaced by DIN 4512-1: 1971-04, DIN 4512-4: 1977-06, DIN 4512-5: 1977-10 and others.
• DIN 4512-1: 1971-04 , DIN 4512-1: 1993-05 . Photographic sensitometry; Black and white negative film systems and their processing for still photography; Determination of photosensitivity . German Institute for Standardization (before 1975: German Standards Committee (DNA)). Replaced by DIN ISO 6: 1996-02.
• DIN 4512-4: 1977-06 , DIN 4512-4: 1985-08 . Photographic sensitometry; Determination of the photosensitivity of color reversal films . German institute for standardization. Replaced by DIN ISO 2240: 1998-06.
• DIN 4512-5: 1977-10 , DIN 4512-5: 1990-11 . Photographic sensitometry; Determination of the light sensitivity of color negative films . German institute for standardization. Replaced by DIN ISO 5800: 1998-06.
• DIN ISO 6: 1996-02 . Photography - Black and white negative film systems and their processing for taking still pictures - Determination of ISO sensitivity (ISO 6: 1993) . German institute for standardization. This is the German implementation of ISO 6: 1993-02.
• DIN ISO 2240: 1998-06 , DIN ISO 2240: 2005-10 . Photography - Camera color reversal films - Determination of ISO sensitivity (ISO 2240: 2003) . German institute for standardization. This is the German implementation of ISO 2240: 2003-10.
• DIN ISO 5800: 1998-06 , DIN ISO 5800: 2003-11 . Photography - Color negative films for still photography - Determination of ISO sensitivity (ISO 5800: 1987 + Corr 1: 2001) . German institute for standardization. This is the German implementation of ISO 5800: 2001-06.
• ASA Z38.2.1-1943, ASA Z38.2.1-1946, ASA Z38.2.1-1947 (July 15, 1947). American Standard Method for Determining Photographic Speed ​​and Speed ​​Number . New York: American Standards Association. Replaced by ASA PH2.5-1954.
• ASA PH2.5-1954, ASA PH2.5-1960. American Standard Method for Determining Speed ​​of photographic Negative Materials (Monochrome, Continuous Tone) . New York: United States of America Standards Institute. Replaced by ANSI PH2.5-1972.
• ANSI PH2.5-1972, ANSI PH2.5-1979 (January 1, 1979), ANSI PH2.5-1979 (R1986). Speed ​​of photographic negative materials (monochrome, continuous tone) . New York: American National Standards Institute. Replaced by NAPM IT2.5-1986.
• NAPM IT2.5-1986, ANSI / ISO 6-1993 ANSI / NAPM IT2.5-1993 (January 1, 1993). Photography - Black-and-White Pictorial Still Camera Negative Film / Process Systems - Determination of ISO Speed ​​(same as ANSI / ISO 6-1993) . National Association of Photographic Manufacturers. This is the US implementation of ISO 6.
• ASA PH2.12-1957, ASA PH2.12-1961. American Standard, General-Purpose Photographic Exposure Meters (photoelectric type) . New York: American Standards Association. Replaced by ANSI PH3.49-1971.
• ANSI PH3.49-1971, ANSI PH3.49-1971 (R1987). American National Standard for general-purpose photographic exposure meters (photoelectric type) . New York: American National Standards Institute. Replaced by ANSI / ISO 2720: 1974 after a number of revisions.
• ANSI / ISO 2720: 1974, ANSI / ISO 2720: 1974 (R1994) ANSI / NAPM IT3.302-1994. General Purpose Photographic Exposure Meters (Photoelectric Type) - Guide to Product Specification . New York: American National Standards Institute. This is the US implementation of ISO 2720.
• BSI BS 1380: 1947, BSI BS 1380: 1963. Speed ​​and exposure index . British Standards Institution. Replaced by BSI BS 1380-1: 1973-12, BSI BS 1380-2: 1984-09, BSI BS 1380-3: 1980-04 and others.
• BSI BS 1380-1: 1973-12 (December 31, 1973). Speed ​​of sensitized photographic materials: Negative monochrome material for still and cine photography . British Standards Institution. Replaced by BSI BS ISO 6: 1993 and BSI BS ISO 2240: 1994.
• BSI BS 1380-2: 1984 ISO 2240: 1982 (September 28, 1984). Speed ​​of sensitized photographic materials. Method for determining the speed of color reversal film for still and amateur cine photography . British Standards Institution. Replaced by BSI BS ISO 2240: 1994.
• BSI BS 1380-3: 1980 ISO 5800: 1979 (April 30, 1980). Speed ​​of sensitized photographic materials. Color negative film for still photography . British Standards Institution. Replaced by BSI BS ISO 5800: 1987.
• BSI BS ISO 6: 1993 (March 15, 1995). Photography. Black-and-white pictorial still camera negative film / process systems. Determination of ISO speed . British Standards Institution. This is the British implementation of ISO 6: 1993-02.
• BSI BS ISO 2240: 1994 (March 15, 1993), BSI BS ISO 2240: 2003 (February 11, 2004). Photography. Color reversal camera films. Determination of ISO speed . British Standards Institution. This is the British implementation of ISO 2240: 2003-10.
• BSI BS ISO 5800: 1987 (March 15, 1995). Photography. Color negative films for still photography. Determination of ISO speed . British Standards Institution. This is the British implementation of ISO 5800: 1987-11.

## Individual evidence

1. Matthias Paul: Information on medium format roll films with barcode identification, barcodes on Fujifilm Brownies . Minolta Forum, accessed on May 18, 2009 (forum post).
2. ^ A b Martin Riat: Graphic Techniques - An introduction to the various techniques and their history. E-book, 3rd German edition, Burriana, spring 2006 ( PDF version v3.0 ), based on a Spanish book Martin Riat: Techniques Grafiques: Una Introduccio a Les Diferents Techniques I a La Seva Historia . 1st edition, Aubert, September 1983, ISBN 84-86243-00-9 .
3. Josef Stüper: The photographic camera from the series Kurt Michel (Hrsg.): The scientific and applied photography - second volume: The photographic camera . Springer-Verlag, Vienna 1962, p. 393, reprinted by Verlag der H. Lindemanns Buchhandlung, Stuttgart 1999, ISBN 3-89506-192-1 (more than 530 pages).
4. a b c d Maurice Fisher: Notes on the Weston light meter models II (until 1956 with Weston scaling) and III (from 1956 with ASA scaling) . English-language article about Johnson of Hendon exposure calculators on Photomemorabilia, updated on March 16, 2010 (accessed July 13, 2011).
5. ^ Re: ISO is amplifier gain on sensor. (nt) - On the technical background of the ISO setting for digital sensors.
6. Weston (Ed.): Weston Film Ratings . Newark, 1946, booklet, 16 pages ( online (PDF; 718 kB), accessed July 28, 2011).
7. General Electric (Ed.): General Electric Film Values . 1947, booklet, 12 pages ( online (PDF; 888 kB), accessed on July 28, 2011).
8. Agon Buchholz: Notes on scaling on General Electric light meters  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.   . In: Article about film speed in kefk-Fotonexus from March 19, 1998, updated January 8, 2006 (accessed July 13, 2011).
9. Maurice Fisher: Notes on the Ilford Speed ​​Group system of Ilford light meters and films . In: Article about Ilford light meters on Photomemorabilia, updated June 5, 2011 (accessed July 13, 2011).
10. Maurice Fisher: Notes on Ilford groups in a picture quotation from Newnes Photographers' Pocket Reference Book, published by George Newnes Ltd, Tower House, Southampton Street, Strand, WC2 (London, UK), ca.1955 . In: Article about Johnson of Hendon exposure calculator on Photomemorabilia, updated on March 16, 2010 (accessed July 13, 2011).
11. a b c Chris Lord: Notes on the Amateur Photographer magazine Exposure Calculator (approx. 1950) . In: English-language article on the history of exposure metering (accessed on July 16, 2011).
12. Erna Padelt, Hansgeorg Laporte: Units and sizes of the natural sciences . Book publisher Leipzig 1967
13. Maurice Fisher: Table with extended Hurter & Driffield value range and some slightly different H&D values ​​in an image quotation from Newnes Photographers' Pocket Reference Book, published by George Newnes Ltd, Tower House, Southampton Street, Strand, WC2 (London, UK) , ca.1955 . In: Article about Johnson of Hendon exposure calculator on Photomemorabilia, updated on March 16, 2010 (accessed July 13, 2011).
14. Chris Lord: Notes on the Cappelli exposure computer with Warnerke numbers, Milan (approx. 1930) . In: English-language article on the history of exposure metering (Accessed July 16, 2011)
15. Maurice Fisher: Notes on Burroughs Wellcome exposure computers (c. 1900 to 1950) by Henry Wellcome and SM Burroughs in an image citation from Newnes Photographers' Pocket Reference Book, published by George Newnes Ltd, Tower House, Southampton Street, Strand, WC2 ( London, UK), ca.1955 . In: Article about Johnson of Hendon exposure calculator on Photomemorabilia, updated on March 16, 2010 (accessed July 13, 2011).
16. a b Maurice Fisher: Notes on Burroughs Wellcome exposure computers (approx. 1900 to 1950) by Henry Wellcome . In: Article about the Johnson of Hedon yearbook on Photomemorabilia, updated September 2, 2010 (accessed August 1, 2011).
17. Hans Windisch: School of color photography . 4th edition, 1951 ("For Agfacolor (negative and reversal) film, a general sensitivity of 12/10 ° DIN = 12 ASAgrade = 16 General Electric = 10 Weston = 22 ° Scheiner is to be assumed.")