Editing Film speed (section)

===Historical systems===

====Warnerke{{anchor|Chapman Jones|Henry Chapman Jones|Jones}}====
<!-- This section is linked from inside or outside this article, preferable by "#Warnerke". Do not rename without keeping in sync. -->
The first known practical [[sensitometry|sensitometer]], which allowed measurements of the speed of photographic materials, was invented by the Polish engineer [[Leon Warnerke]]<ref name="DIN_1934_DIN-4512_Introduction"/>&nbsp;– pseudonym of {{lang|pl|[[Władysław Małachowski]]}} (1837–1900)&nbsp;– in 1880, among the achievements for which he was awarded the [[Progress Medal (RPS)|Progress Medal]] of the [[Photographic Society of Great Britain]]<!-- Today named: Royal Photographic Society (RPS) --> in 1882.<ref name="RPS_2011_Progress_Medal_1882"/><ref name="Jones_1911_Cyclopaedia"/> It was commercialized since 1881.

The Warnerke Standard Sensitometer consisted of a frame holding an opaque screen with an array of typically 25 numbered, gradually pigmented squares brought into contact with the photographic plate during a timed test exposure under a [[Phosphorescence|phosphorescent]] tablet excited before by the light of a burning [[magnesium]] ribbon.<ref name="Jones_1911_Cyclopaedia"/> The speed of the emulsion was then expressed in 'degrees' Warnerke (sometimes seen as Warn. or °W.) corresponding with the last number visible on the exposed plate after development and fixation. Each number represented an increase of 1/3 in speed, typical plate speeds were between 10° and 25° Warnerke at the time.<!-- According to Josef Maria Eder - History of photography: p. 451: 20° Warnerke = 10° (European) Scheiner, 24-25° Warnerke = 16-18° (European) Scheiner. -->

His system saw some success but proved to be unreliable<ref name="DIN_1934_DIN-4512_Introduction"/> due to its spectral sensitivity to light, the fading intensity of the light emitted by the phosphorescent tablet after its excitation as well as high built-tolerances.<ref name="Jones_1911_Cyclopaedia"/> The concept, however, was later built upon in 1900 by [[Henry Chapman Jones]] (1855–1932)<!-- 1932-03-07 --> in the development of his<!-- So called Chapman Jones --> plate tester and modified speed system.<ref name="Jones_1911_Cyclopaedia"/><ref name="Hasluck_1905_Jones"/>

====Hurter &amp; Driffield{{anchor|H&D}}====
<!-- This section is linked from inside or outside this article, preferable by "#H&D". Do not rename without keeping in sync. -->
Another early practical system for measuring the sensitivity of an emulsion was that of [[Hurter and Driffield]] (H&D), originally described in 1890, by the Swiss-born [[Ferdinand Hurter]] (1844–1898) and British [[Vero Charles Driffield]] (1848–1915). In their system, speed numbers were inversely proportional to the exposure required. For example, an emulsion rated at 250&nbsp;H&D would require ten times the exposure of an emulsion rated at 2500&nbsp;H&D.<ref name="Sowerby"/>

The methods to determine the sensitivity were later modified in 1925 (in regard to the light source used) and in 1928 (regarding light source, developer and proportional factor)—this later variant was sometimes called "H&D&nbsp;10". The H&D system was officially<ref name="Konovalov_2007"/><!-- TBD: I found documents stating that there was no standard before 1945, so we should find some historic documents stating that H&D (or whatever) was really an *official* standard in the USSR, and not just semi-standard. Also, since GOST 2817-45 was apparently first defined in 1945, why was the GOST standard not introduced before 1951, when its revision GOST 2817-50 was already in place? Runner1616: Until 1951 both standards existed simultaneously in USSR. Any photo book before 1950 operated with H&D (Х и Д) --> accepted as a standard in the former [[Soviet Union]] from 1928 until September 1951, when it was superseded by [[#GOST|GOST]]&nbsp;2817–50.

====Scheiner{{anchor|Scheinergrade|Sch|Sch.}}====
<!-- This section is linked from inside or outside this article, preferable by "#Scheiner". Do not rename without keeping in sync. -->
The ''Scheinergrade'' (Sch.) system was devised by the German astronomer [[Julius Scheiner]] (1858–1913) in 1894 originally as a method of comparing the speeds of plates used for astronomical photography. Scheiner's system rated the speed of a plate by the least exposure to produce a visible darkening upon development. Speed was expressed in degrees Scheiner, originally ranging from 1° to 20°&nbsp;Sch., with each increment of a degree corresponding to a ''multiplicative'' factor of increased light sensitivity. This multiplicative factor was determined by the constraint that an increment of 19° Sch. (from 1° to 20°&nbsp;Sch.) corresponded to a hundredfold increase in sensitivity. Thus emulsions that differed by 1° Sch. on the Scheiner scale were <math>\sqrt[19]{100} = 1.2742...</math>-fold more (or, less) sensitive to each other. An increment of 3°&nbsp;Sch. came close to a doubling of sensitivity<ref name ="Sowerby"/><ref name="Riat_2006"/> <math>(\sqrt[19]{100})^3 = 2.06914...</math>.

The system was later extended to cover larger ranges and some of its practical shortcomings were addressed by the Austrian scientist [[Josef Maria Eder]] (1855–1944)<ref name="DIN_1934_DIN-4512_Introduction"/> and Flemish-born botanist {{Interlanguage link multi|Walter Hecht|de|3=Walter Hecht}} (1896–1960), (who, in 1919/1920, jointly developed their ''Eder–Hecht neutral wedge sensitometer'' measuring emulsion speeds in ''Eder–Hecht'' grades). It remained difficult for manufacturers to reliably determine film speeds, often only by comparing with competing products,<ref name="DIN_1934_DIN-4512_Introduction"/> so that an increasing number of modified semi-Scheiner-based systems started to spread, which no longer followed Scheiner's original procedures and thereby defeated the idea of comparability.<ref name="DIN_1934_DIN-4512_Introduction"/><ref name="Sheppard_1932_Dresden-Congress"/>

Scheiner's system was eventually abandoned in Germany, when the standardized [[#DIN|DIN]] system was introduced in 1934. In various forms, it continued to be in widespread use in other countries for some time.

====DIN{{anchor|DIN 4512|DIN 4512-1|DIN 4512-4|DIN 4512-5}}====
<!-- This section is linked from inside or outside this article, preferable by "#DIN. Do not rename without keeping in sync. -->
The DIN system, officially DIN standard 4512 by the ''{{lang|de|[[Deutsches Institut für Normung]]}}'' (then known as the ''{{lang|de|Deutscher Normenausschuß}}''<!-- Sic, old German spelling, no typos here. --> (DNA)), was published in January 1934. It grew out of drafts for a standardized method of sensitometry put forward by the ''{{lang|de|Deutscher Normenausschuß für Phototechnik}}''<!-- Sic, old German spelling, no typos here. --><ref name="Sheppard_1932_Dresden-Congress"/> as proposed by the committee for sensitometry of the ''{{lang|de|Deutsche Gesellschaft für photographische Forschung}}''<ref name="Biltz_1933_DIN-Grade"/> since 1930<ref name="Heisenberg_1930_Tagung"/><ref name="Voss_2002_Luther"/> and presented by {{Interlanguage link multi|Robert Thomas Dietrich Luther{{!}}Robert Luther|de|3=Robert Thomas Dietrich Luther}}<ref name="Voss_2002_Luther"/><ref name="Buckland_2008_Kinamo"/> (1868–1945)<!-- 1868-01-02 (21. December 1867 in Julian caldendar) to 1945-04-17, chemist. --> and [[Emanuel Goldberg]]<ref name="Buckland_2008_Kinamo"/> (1881–1970) at the influential VIII. [[International Congress of Photography]] (German: ''{{lang|de|Internationaler Kongreß für wissenschaftliche und angewandte Photographie}}''<!-- Sic, old German spelling, no typos here. -->) held in [[Dresden]] from 3 to 8 August 1931.<ref name="Sheppard_1932_Dresden-Congress"/><ref name="Eggert_1932_Kongress-Bericht"/>

The DIN system was inspired by [[#Scheiner|Scheiner]]'s system,<ref name="DIN_1934_DIN-4512_Introduction"/> but the sensitivities were represented as the base 10 logarithm of the sensitivity multiplied by 10, similar to [[decibel]]s. Thus an increase of 20° (and not 19° as in Scheiner's system) represented a hundredfold increase in sensitivity, and a difference of 3° was much closer to the base 10 logarithm of 2 (0.30103...):<ref name="Riat_2006"/>

:<math>\log_{10}{(2)} = 0.30103... \approx 3/10</math>.

[[File:Agfacolor neu - 7300960484.jpg|thumb|A box of [[Agfacolor|Agfacolor Neu]] with the instruction "expose as 15/10° DIN" (in German)]]

As in the Scheiner system, speeds were expressed in 'degrees'. Originally the sensitivity was written as a fraction with 'tenths' (for example "18/10°&nbsp;DIN"),<ref name="Benser_1957_Farbig"/> where the resultant value 1.8 represented the relative base 10 logarithm of the speed. 'Tenths' were later abandoned with DIN&nbsp;4512:1957-11, and the example above would be written as "18°&nbsp;DIN".<ref name="Sowerby"/> The degree symbol was finally dropped with DIN&nbsp;4512:1961-10. This revision also saw significant changes in the definition of film speeds in order to accommodate then-recent changes in the American [[#ASA|ASA]] PH2.5-1960 standard, so that film speeds of black-and-white negative film effectively would become doubled, that is, a film previously marked as "18° DIN"<!-- With degree symbol. --> would now be labeled as "21&nbsp;DIN"<!-- Without degree symbol. --> without emulsion changes.

Originally only meant for black-and-white negative film, the system was later extended and regrouped into nine parts, including DIN&nbsp;4512-1:1971-04 for black-and-white negative film, DIN&nbsp;4512-4:1977-06 for color reversal film and DIN&nbsp;4512-5:1977-10 for color negative film.

On an international level the German DIN 4512 system has been effectively superseded in the 1980s by ISO&nbsp;6:1974,<ref name="ISO_6"/> ISO&nbsp;2240:1982,<ref name="http"/> and ISO&nbsp;5800:1979<ref name="iso.org"/> where the same sensitivity is written in linear and logarithmic form as "ISO&nbsp;100/21°" (now again with degree symbol). These [[#ISO|ISO]] standards were subsequently adopted by DIN as well. Finally, the latest DIN&nbsp;4512 revisions were replaced by corresponding ISO standards, DIN&nbsp;4512-1:1993-05 by DIN&nbsp;ISO&nbsp;6:1996-02 in September 2000, DIN&nbsp;4512-4:1985-08 by DIN&nbsp;ISO&nbsp;2240:1998-06 and DIN&nbsp;4512-5:1990-11 by DIN&nbsp;ISO&nbsp;5800:1998-06 both in July 2002.<!-- DIN 4512-3:1973-01 was replaced by DIN 4512-7:1993-01, DIN 4512-8:1993-01 and DIN 4512-9:1993-01. DIN 4512-6:1980-07 was withdrawn. As far as I know, DIN 4512-7:1993-01, DIN 4512-8:1993-01, DIN 4512-9:1993-01 as well as DIN 4512-10:1993-01 are still active as of this writing (2011–07), but don't define film speeds. -->

====BSI{{anchor|BS}}====
When [[British Standards Institution|BS]]&nbsp;935:1941 was published during [[World War II]], specifying exposure tables for negative materials, it employed the same [[#Fixed density|fixed-density]] speed criterion used in the German [[Deutsches Institut für Normung|DIN]]&nbsp;4512:1934 system. The British Standard also used ''logarithmic'' speed numbers, following the example of [[#Scheiner|Scheiner]] and DIN. When the American ASA&nbsp;Z38.2.1:1943 standard was published, it used a [[#Fractional gradient|fractional gradient]] speed criterion and ''arithmetic'' speed numbers, for compatibility with [[Edward Weston|Weston]] and [[GE]].<ref>{{citation
 | last = Jacobson | first = Ralph E
 | publisher = Focal Press 
 | title = The Manual of Photography (Seventh Edition)
 | page = 412
 | year = 1978}}
</ref>

British standard BS&nbsp;1380:1947 adopted the ''fractional gradient'' criterion of the American 1943 standard, and also included ''arithmetic'' speed numbers in addition to ''logarithmic'' numbers.<ref>{{citation
 | last = Jacobson | first = Ralph E
 | publisher = Focal Press 
 | title = The Manual of Photography (Seventh Edition)
 | page = 412
 | year = 1978}}
</ref> The ''logarithmic'' speed number proposed in the later BS&nbsp;1380:1957 standard was almost identical to the DIN&nbsp;4512:1957 standard, except that the BS number was +9 degrees greater than the corresponding DIN number; in 1971, the BS and DIN standards changed this to +10&nbsp;degrees.<ref>{{citation
 | last1 = Dunn | first1 = Jack F
 | last2 = Wakefield | first2 = George L
 | publisher = Fountain Press 
 | title = Exposure Manual (Fourth Edition)
 | page = 22
 | year = 1981}}
</ref>

Following an increasing effort to produce international standards, the British, American, and German standards became identical in ISO&nbsp;6:1974, which corresponded to BS&nbsp;1380:Part1:1973.<ref>{{citation
 | last = Allbright | first = G S
 | journal = The Journal of Photographic Science
 | doi = 10.1080/00223638.1991.11737126
 | title = Emulsion Speed Rating Systems
 | year = 1991| volume = 39
 | issue = 2
 | pages = 95–99
 }}
</ref>

====Weston{{anchor|Weston film speed ratings}}====

[[File:Weston 650 Light Meter July 2015.jpg|thumb|Weston Model 650 [[light meter]] from about 1935]]
[[File:Weston Master Light Meter July 2015.jpg|thumb|Early Weston Master light meter 1935–1945]]

<!-- This section is linked from inside or outside this article, preferable by "#Weston". Do not rename without keeping in sync. -->
Before the advent of the ASA system, the system of ''Weston film speed ratings'' was introduced by [[Edward Faraday Weston]]<!-- No relation with [[Edward Henry Weston]], the photographer. --> (1878–1971) and his father Dr. [[Edward Weston (chemist)|Edward<!-- W.? - see comment below. --> Weston]]<!-- no relation with [[Edward Henry Weston]], the famous photographer --> (1850–1936), a British-born electrical engineer, industrialist and founder of the US-based [[Weston Electrical Instrument Corporation]],<ref name="Mulhern_1990_Letter"/><!-- Note: Both above mentioned patents of Edward F. Weston do not apply to the Weston 617 and the speed rating system. --> with the Weston model 617, one of the earliest photo-electric exposure meters, in August 1932. The meter and film rating system were invented by [[William Nelson Goodwin, Jr.]],<ref name="Goodwin_1938_emulsion_ratings"/><ref name="Roseborough_1996_PHSC-PC-22-3"/> who worked for them<ref name="Tipper_Weston"/><!-- In the Weston Master II model 735 manual (dated 1948?) Weston claimed the Weston film speed rating system was in use for over 15 years already. Reportedly, the Master II was introduced as early as 1945. The manual of the Master Universal model 715 (1939) explicitly mentioned the speed ratings already. The manual of the Universal model 650 (1937) seems to mention them to, but does not name them as such. Goodwin published "Weston emulsion speed ratings" in 1938. So they must have been introduced between 1932 and 1938. --> and later received a [[Howard N. Potts Medal]] for his contributions to engineering.<!-- Franklin Institute, Howard N. Potts Medal, 1958, Engineering, "Contributions to the fields of electrical measuring instruments, and for work on photoelectric exposure meters and establishing a scale for film speeds." http://www.fi.edu/winners/detail.faw?winner_id=2912 --><!-- Goodwin's patents regarding exposure meters: "Photographic exposure meter", US patent 2073790, filed: 1932-10-21, issued 1937-03-16, https://www.google.com/patents/about?id=txdQAAAAEBAJ. "Photoelectric cell circuit", US patent 2032010, filed 1933-06-23, issued 1936-02-25, https://www.google.com/patents/about?id=lixMAAAAEBAJ. "Photoelectric cell circuit", US patent RE20823, filed 1933-06-23, issued 1938-08-09, https://www.google.com/patents/about?id=724CAAAAEBAJ -->

The company tested and frequently published speed ratings for most films of the time. Weston film speed ratings could since be found on most Weston exposure meters and were sometimes referred to by film manufacturers and third parties<ref name="Hefley_1951_micrographs"/> in their exposure guidelines. Since manufacturers were sometimes creative about film speeds, the company went as far as to warn users about unauthorized uses of their film ratings in their "Weston film ratings" booklets.<ref name="Weston_1946_Ratings"/>

The Weston Cadet (model 852 introduced in 1949), Direct Reading (model 853 introduced 1954) and Master III (models 737 and S141.3 introduced in 1956) were the first in their line of exposure meters to switch and utilize the meanwhile established ASA scale instead. Other models used the original Weston scale up until ca. 1955. The company continued to publish Weston film ratings after 1955,<ref name="Sangamo_1959_Weston-Ratings"/><!-- TBD: Did Weston also publish ratings after the ASA PH2.5-1960 changes? --> but while their recommended values often differed slightly from the ASA film speeds found on film boxes, these newer Weston values were based on the ASA system and had to be converted for use with older Weston meters by subtracting 1/3 exposure stop as per Weston's recommendation.<ref name="Sangamo_1959_Weston-Ratings"/> Vice versa, "old" Weston film speed ratings could be converted into "new" Westons and the ASA scale by adding the same amount, that is, a film rating of 100 Weston (up to 1955) corresponded with 125 ASA (as per ASA PH2.5-1954 and before). This conversion was not necessary on Weston meters manufactured and Weston film ratings published since 1956 due to their inherent use of the ASA system;<!-- temporary sentence follows: --> however the changes of the ASA PH2.5-1960 revision may be taken into account when comparing with newer ASA or ISO values.<!-- Comparing historical black-and-white negative film speeds given in old Westons with newer ASA values (as per ASA PH2.5-1960) or [[#ISO|ISO]] film speeds may require to add another full exposure stop to the effect of actually adding 1.3 EV to that Weston value in order to find the ISO/ASA equivalent.--><!-- TBD: In order to prove this statement it would be most interesting to learn about Weston speed ratings published after the ASA PH2.5-1960 revision, if they exist. -->

====General Electric{{anchor|GE|General Electric film values}}====
<!-- This section is linked from inside or outside this article, preferable by "#GE". Do not rename without keeping in sync. -->
Prior to the establishment of the ASA scale<ref name="General-Electric_194x_GES-2810_Manual_GW-68"/> and similar to [[#Weston|Weston film speed ratings]] another manufacturer of photo-electric exposure meters, [[General Electric]], developed its own rating system of so-called ''General Electric film values'' (often abbreviated as ''G-E'' or ''GE'') around 1937.<!-- The exposure meter GW-47 is dated 1937 and has GE "film value" scale. -->

Film speed values for use with their meters were published in regularly updated ''General Electric Film Values''<ref name="General-Electric_1947_GED-744_Film-Values"/> leaflets and in the ''General Electric Photo Data Book''.<ref name="General-Electric_1942_GET-I717"/>

General Electric switched to use the [[#ASA|ASA]] scale in 1946. Meters manufactured since February 1946 are equipped with the ASA scale (labeled "Exposure Index") already. For some of the older meters with scales in "Film Speed" or "Film Value" (e.g. models DW-48, DW-49 as well as early DW-58 and GW-68 variants), replaceable hoods with ASA scales were available from the manufacturer.<ref name="General-Electric_1947_GED-744_Film-Values"/><ref name="General-Electric_1946_Ad_Hood"/> The company continued to publish recommended film values after that date, however, they were then aligned to the ASA scale.

====ASA{{anchor|APEX|ASA PH2.5|ASA Z38.2.1}}====
<!-- This section is linked from inside or outside this article, preferable by "#ASA". Do not rename without keeping in sync. -->
Based on earlier research work by [[Loyd A. Jones|Loyd Ancile Jones]] (1884–1954) of [[Kodak]]<!-- TBD: Original name of Kodak system was "Kodak speed" since 1939 --> and inspired by the systems of [[#Weston|Weston film speed ratings]]<ref name="Sangamo_1959_Weston-Ratings"/> and [[#GE|General Electric film values]],<ref name="General-Electric_1947_GED-744_Film-Values"/> the [[American Standards Association]] (now named ANSI) defined a new method to determine and specify film speeds of black-and-white negative films in 1943. ASA&nbsp;Z38.2.1–1943 was revised in 1946 and 1947 before the standard grew into ASA PH2.5-1954. Originally, ASA values were frequently referred to as ''American standard speed numbers'' or ''ASA exposure-index numbers''. (See also: [[#EI|Exposure Index]] (EI).)

The ASA scale is a linear scale, that is, a film denoted as having a film speed of 200&nbsp;ASA is twice as fast as a film with 100&nbsp;ASA.

The ASA standard underwent a major revision in 1960 with ASA PH2.5-1960, when the method to determine film speed was refined and previously applied safety factors against under-exposure were abandoned, effectively doubling the nominal speed of many black-and-white negative films. For example, an [[Ilford HP|Ilford HP3]] that had been rated at 200&nbsp;ASA before 1960 was labeled 400&nbsp;ASA afterwards without any change to the emulsion. Similar changes were applied to the [[#DIN|DIN]] system with DIN 4512:1961-10 and the BS system with BS 1380:1963 in the following years.

In addition to the established arithmetic speed scale, ASA PH2.5-1960 also introduced logarithmic ASA grades (100 ASA = 5° ASA), where a difference of 1° ASA represented a full exposure stop and therefore the doubling of a film speed. For some while, ASA grades were also printed on film boxes, and they saw life in the form of the [[APEX system|APEX]] speed value ''S<sub>v</sub>'' (without degree symbol) as well.

ASA PH2.5-1960 was revised as ANSI PH2.5-1979, without the logarithmic speeds, and later replaced by NAPM&nbsp;IT2.5–1986 of the National Association of Photographic Manufacturers, which represented the US adoption of the international standard ISO&nbsp;6. The latest issue of ANSI/NAPM IT2.5 was published in 1993.

The standard for color negative film was introduced as ASA PH2.27-1965 and saw a string of revisions in 1971, 1976, 1979, and 1981, before it finally became ANSI IT2.27–1988 prior to its withdrawal.

Color reversal film speeds were defined in ANSI PH2.21-1983, which was revised in 1989 before it became ANSI/NAPM&nbsp;IT2.21 in 1994, the US adoption of the ISO&nbsp;2240 standard.

On an international level, the ASA system was superseded by the [[#ISO|ISO]] film speed system between 1982 and 1987, however, the arithmetic ASA speed scale continued to live on as the linear speed value of the ISO system.

====GOST{{anchor|GOST 2817|GOST 10691}}====
<!-- This section is linked from inside or outside this article, preferable by "#GOST". Do not rename without keeping in sync. -->
[[File:Svema-film-65.jpg|thumb|A box of [[Svema]] film, with a sensitivity of 65 [[GOST]] (ГОСТ)]]
{{lang|ru-Latn|[[GOST]]|italic=no}} (Cyrillic: {{lang|ru|ГОСТ}}) was an arithmetic film speed scale defined in GOST&nbsp;2817-45 and GOST&nbsp;2817–50.<ref name="Gorokhovskiy_1970_Metrologiya"/><ref name="GOST_2817-50"/> It was used in the former [[Soviet Union]] since October 1951,{{Citation needed|date=August 2011}}<!-- TBD: Why not earlier when GOST 2817-45 was defined earlier? --> replacing Hurter & Driffield (H&D, Cyrillic: ХиД) numbers,<ref name="Gorokhovskiy_1970_Metrologiya"/> which had been used since 1928.{{Citation needed|date=August 2011}}

GOST 2817-50 was similar to the ASA standard, having been based on a speed point at a density 0.2 above base plus fog, as opposed to the ASA's&nbsp;0.1.<ref name="Stroebel_1993_Encyclopedia"/> GOST markings are only found on pre-1987 photographic equipment (film, cameras, [[Light meter|lightmeters]], etc.) of Soviet Union manufacture.<ref name="ZENIT_2011_GOST"/>

On 1 January 1987, the GOST scale was realigned to the [[#ISO|ISO]] scale with GOST&nbsp;10691–84,<ref name="GOST_10691-84"/>

This evolved into multiple parts including GOST&nbsp;10691.6–88<ref name="GOST_10691.6-88"/> and GOST&nbsp;10691.5–88,<ref name="GOST_10691.5-88"/> which both became functional on 1 January 1991.<!-- Also found "GOST 10691-63" and various other GOST 10691.x-xx variants. -->