Film speed - WikiHQ

thumb|right|This film container denotes its speed as ISO 100/21°, including both arithmetic (100 ASA) and logarithmic (21 DIN) components. The second is often dropped, making (e.g.) "ISO 100" effectively equivalent to the older ASA speed. (As is common, the "100" in the film name alludes to its ISO rating.)

Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system introduced in 1974. A closely related system, also known as ISO, is used to describe the relationship between exposure and output image lightness in digital cameras. Prior to ISO, the most common systems were ASA in the United States and DIN in Europe.

The term speed comes from the early days of photography. Photographic emulsions that were more sensitive to light needed less time to generate an acceptable image and thus a complete exposure could be finished faster, with the subjects having to hold still for a shorter length of time. Emulsions that were less sensitive were deemed "slower" as the time to complete an exposure was much longer and often usable only for still life photography. Exposure times for photographic emulsions shortened from hours to fractions of a second by the late 19th century.

In both film and digital photography, choice of speed will almost always affect image quality. Higher sensitivities, which require shorter exposures, typically result in reduced image quality due to coarser film grain or increased digital image noise. Lower sensitivities, which require longer exposures, will retain more viable image data due to finer grain or less noise, and therefore more detail. Ultimately, sensitivity is limited by the quantum efficiency of the film or sensor.

To determine the exposure time needed for a given film, a light meter is typically used.

Film speed measurement systems

Emulsion speed rating criteria

Five criteria for the rating of emulsion speed have been used since the late 19th century, listed here by name and date, these criteria are: threshold (1880), inertia (1890), fixed density (1934), minimum useful gradient (1939) and fractional gradient (1939).

Threshold

The threshold criterion is the point on the characteristic curve corresponding to just perceptible density above fog.

Inertia

The inertia speed point of an emulsion is determined on the Hurter and Driffield characteristic curve by the intercept between the gradient of the straight line part of the curve and the line representing the base + fog (B+F) on the density axis.

Fixed density

The fixed density speed point is determined by defining a fixed minimum density as the basis of the emulsion speed (e.g. 0.1 above B+F).

Minimum useful gradient

The minimum useful gradient criterion places the speed point where the gradient first reaches an agreed value (e.g. tan <big>𝜃</big> = 0.2).

Fractional gradient

The fractional gradient is defined as the speed point at which the slope of the characteristic curve first reaches a fixed fraction (e.g. 0.3) of the average gradient over a range (e.g. 1.5) of the characteristic curve.

Historical systems

Warnerke

The first known practical sensitometer, which allowed measurements of the speed of photographic materials, was invented by the Polish engineer Leon Warnerke

British standard BS 1380:1947 adopted the fractional gradient criterion of the American 1943 standard, and also included arithmetic speed numbers in addition to logarithmic numbers. The logarithmic speed number proposed in the later BS 1380:1957 standard was almost identical to the DIN 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 degrees.

Following an increasing effort to produce international standards, the British, American, and German standards became identical in ISO 6:1974, which corresponded to BS 1380:Part1:1973.

Weston

thumb|Weston Model 650 [[light meter from about 1935]]

thumb|Early Weston Master light meter 1935–1945

Before the advent of the ASA system, the system of Weston film speed ratings was introduced by Edward Faraday Weston (1878–1971) and his father, Edward Weston (1850–1936), a British-born electrical engineer, industrialist and founder of the US-based Weston Electrical Instrument Corporation,

| 1/1°

| 1

| (1)

| Svema Micrat-orto, Astrum Micrat-orto

| 1.2/2°

| 1.2

| 2

| (1)

|- style="background:#ffe"

| −1

| 1.6/3°

| 1.6

| 3

| 1.4

| 2/4°

| 2

| 4

| (2)

| 2.5/5°

| 2.5

| 5

| (2)

|- style="background:#ffe"

| 0

| 3/6°

| 3

| 6

| 2.8

| Svema MZ-3, Astrum MZ-3

| 4/7°

| 4

| 7

| (4)

| 5/8°

| 5

| 8

| (4)

| Original three-strip Technicolor

|- style="background:#ffe"

| 1

| 6/9°

| 6

| 9

| 5.5

| Original Kodachrome

| 8/10°

| 8

| 10

| (8)

| Polaroid PolaBlue

| 10/11°

| 10

| 11

| (8)

| Kodachrome 8mm film

|- style="background:#ffe"

| 2

| 12/12°

| 12

| 11

| Gevacolor 8mm reversal film, later Agfa Dia-Direct

| 16/13°

| 16

| 13

| (16)

| Agfacolor 8mm reversal film

| 20/14°

| 20

| 14

| (16)

| Adox CMS 20

|- style="background:#ffe"

| 3

| 25/15°

| 25

| 15

| 22

| Old Agfacolor, KodachromeII and (later) Kodachrome 25, Efke 25

| 32/16°

| 32

| 16

| (32)

| Kodak Panatomic-X

| 40/17°

| 40

| 17

| (32)

| Kodachrome 40 (movie)

|- style="background:#ffe"

| 4

| 50/18°

| 50

| 18

| 45

| Fuji RVP (Velvia), Ilford Pan F Plus, Kodak Vision 250D 5201 (movie), AGFA CT18, Efke 50, Polaroid type 55

| 64/19°

| 64

| 19

| (65)

| Kodachrome 64, Ektachrome-X, Polaroid type 64T

| 80/20°

| 80

| 20

| (65)

| Ilford Commercial Ortho, Polaroid type669

|- style="background:#ffe"

| 5

| 100/21°

| 100

| 21

| 90

| Kodak T-MAX 100 (TMX), Kodak Ektar, Fujichrome Provia 100F, Fujifilm Acros 100 II Efke 100, Fomapan/Arista 100, Kentmere Pan 100

| 125/22°

| 125

| 22

| (130)

| Ilford FP4+, Kodak Plus-X Pan, Svema Color 125

| 160/23°

| 160

| 23

| (130)

| Fujicolor Pro 160C/S, Kodak High-Speed Ektachrome, Kodak Portra 160NC and 160VC

|- style="background:#ffe"

| 6

| 200/24°

| 200

| 24

| 180

| Kodak Gold 200, Fujicolor Superia 200, Agfa Scala 200x, Fomapan/Arista 200, Wittner Chrome 200D, Agfa Aviphot Chrome 200 PE1

| 250/25°

| 250

| 25

| (250)

| Tasma Foto-250, Eastman Double-X

| 320/26°

| 320

| 26

| (250)

| Kodak Tri-X Pan Professional (TXP)

|- style="background:#ffe"

| 7

| 400/27°

| 400

| 27

| 350

| Kodak T-Max400 (TMY), Kodak Tri-X 400, Kodak Portra 400, Ilford HP5+, Fujifilm Superia X-tra 400, Fujichrome Provia 400X, Fomapan/Arista 400, KentmerePan 400

| 500/28°

| 500

| 28

| (500)

| Kodak Vision3500T5219 (movie)

| 640/29°

| 640

| 29

| (500)

| Polaroid600

|- style="background:#ffe"

| 8

| 800/30°

| 800

| 30

| 700

| Fuji Pro 800Z, Fuji Instax

| 1000/31°

| 1000

| 31

| (1000)

| Ilford Delta 3200, Kodak P3200 TMAX

|- style="background:#ffe"

| 13

| 25000/45°

</references>

ISO 6:1974, ISO 6:1993 (1993-02). Photography — Black-and-white pictorial still camera negative film/process systems — Determination of ISO speed. Geneva: International Organization for Standardization.
ISO 2240:1982 (1982-07), ISO 2240:1994 (1994-09), ISO 2240:2003 (2003–10). Photography — Colour reversal camera films — Determination of ISO speed. Geneva: International Organization for Standardization.
ISO 2720:1974. General Purpose Photographic Exposure Meters (Photoelectric Type) — Guide to Product Specification. Geneva: International Organization for Standardization.
ISO 5800:1979, ISO 5800:1987 (1987-11), ISO 5800:1987/Cor 1:2001 (2001-06). Photography — Colour negative films for still photography — Determination of ISO speed. Geneva: International Organization for Standardization.
ISO 12232:1998 (1998-08), ISO 12232:2006 (2006-04-15), ISO 12232:2006 (2006-10-01), ISO 12232:2019 (2019-02-01). Photography — Digital still cameras — Determination of exposure index, ISO speed ratings, standard output sensitivity, and recommended exposure index. Geneva: International Organization for Standardization.
ASA Z38.2.1-1943, ASA Z38.2.1-1946, ASA Z38.2.1-1947 (1947-07-15). American Standard Method for Determining Photographic Speed and Speed Number. New York: American Standards Association. Superseded 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 (USASI). Superseded by ANSI PH2.5-1972.
ANSI PH2.5-1972, ANSI PH2.5-1979 (1979-01-01), ANSI PH2.5-1979(R1986). Speed of photographic negative materials (monochrome, continuous tone, method for determining). New York: American National Standards Institute. Superseded by NAPM IT2.5-1986.
NAPM IT2.5-1986, ANSI/ISO 6-1993 ANSI/NAPM IT2.5-1993 (1993-01-01). 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 represents the US adoption 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. Superseded by ANSI PH3.49-1971.
ANSI PH2.21-1983 (1983-09-23), ANSI PH2.21-1983(R1989). Photography (Sensitometry) Color reversal camera films – Determination of ISO speed. New York: American Standards Association. Superseded by ANSI/ISO 2240-1994 ANSI/NAPM IT2.21-1994.
ANSI/ISO 2240-1994 ANSI/NAPM IT2.21-1994. Photography – Colour reversal camera films – determination of ISO speed. New York: American National Standards Institute. This represents the US adoption of ISO 2240.
ASA PH2.27-1965 (1965-07-06), ASA PH2.27-1971, ASA PH2.27-1976, ANSI PH2.27-1979, ANSI PH2.27-1981, ANSI PH2.27-1988 (1988-08-04). Photography – Colour negative films for still photography – Determination of ISO speed (withdrawn). New York: American Standards Association. Superseded by ANSI IT2.27-1988.
ANSI IT2.27-1988 (1994-08/09?). Photography Color negative films for still photography – Determination of ISO speed. New York: American National Standards Institute. Withdrawn. This represented the US adoption of ISO 5800.
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. After several revisions, this standard was withdrawn in favor of ANSI/ISO 2720:1974.
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 represents the US adoption of ISO 2720.
BSI BS 1380:1947, BSI BS 1380:1963. Speed and exposure index. British Standards Institution. Superseded by BSI BS 1380-1:1973 (1973-12), BSI BS 1380-2:1984 (1984-09), BSI BS 1380-3:1980 (1980-04) and others.
BSI BS 1380-1:1973 (1973-12-31). Speed of sensitized photographic materials: Negative monochrome material for still and cine photography. British Standards Institution. Replaced by BSI BS ISO 6:1993, superseded by BSI BS ISO 2240:1994.
BSI BS 1380-2:1984 ISO 2240:1982 (1984-09-28). Speed of sensitized photographic materials. Method for determining the speed of colour reversal film for still and amateur cine photography. British Standards Institution. Superseded by BSI BS ISO 2240:1994.
BSI BS 1380-3:1980 ISO 5800:1979 (1980-04-30). Speed of sensitized photographic materials. Colour negative film for still photography. British Standards Institution. Superseded by BSI BS ISO 5800:1987.

BSI BS ISO 6:1993 (1995-03-15). Photography. Black-and-white pictorial still camera negative film/process systems. Determination of ISO speed. British Standards Institution. This represents the British adoption of ISO 6:1993.
BSI BS ISO 2240:1994 (1993-03-15), BSI BS ISO 2240:2003 (2004-02-11). Photography. Colour reversal camera films. Determination of ISO speed. British Standards Institution. This represents the British adoption of ISO 2240:2003.
BSI BS ISO 5800:1987 (1995-03-15). Photography. Colour negative films for still photography. Determination of ISO speed. British Standards Institution. This represents the British adoption of ISO 5800:1987.
DIN 4512:1934-01, DIN 4512:1957-11 (Blatt 1), DIN 4512:1961-10 (Blatt 1). Photographische Sensitometrie, Bestimmung der optischen Dichte. Berlin: Deutscher Normenausschuß (DNA). Superseded 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; systems of black and white negative films and their process for pictorial photography; determination of speed. Berlin: Deutsches Institut für Normung (before 1975: Deutscher Normenausschuß (DNA)). Superseded by DIN ISO 6:1996-02.

DIN 4512-4:1977-06 , DIN 4512-4:1985-08 . Photographic sensitometry; determination of the speed of colour reversal films. Berlin: Deutsches Institut für Normung. Superseded by DIN ISO 2240:1998-06.
DIN 4512-5:1977-10 , DIN 4512-5:1990-11 . Photographic sensitometry; determination of the speed of colour negative films. Berlin: Deutsches Institut für Normung. Superseded by DIN ISO 5800:1998-06.

DIN ISO 6:1996-02 . Photography – Black-and-white pictorial still camera negative film/process systems – Determination of ISO speed (ISO 6:1993). Berlin: Deutsches Institut für Normung. This represents the German adoption of ISO 6:1993.
DIN ISO 2240:1998-06 , DIN ISO 2240:2005-10 . Photography – Colour reversal camera films – Determination of ISO speed (ISO 2240:2003). Berlin: Deutsches Institut für Normung. This represents the German adoption of ISO 2240:2003.
DIN ISO 5800:1998-06 , DIN ISO 5800:2003-11 . Photography – Colour negative films for still photography – Determination of ISO speed (ISO 5800:1987 + Corr. 1:2001). Berlin: Deutsches Institut für Normung. This represents the German adoption of ISO 5800:2001.
Leslie B. Stroebel, John Compton, Ira Current, Richard B. Zakia. Basic Photographic Materials and Processes, second edition. Boston: Focal Press, 2000. .

External links

What is the meaning of ISO for digital cameras? Digital Photography FAQ
Signal-dependent noise modeling, estimation, and removal for digital imaging sensors

"Handbook of Photography" by Henney and Dudley (1939) Spreadsheet Comparing Film Speed Systems

Film speed measurement systems

Emulsion speed rating criteria

Threshold

Inertia

Fixed density

Minimum useful gradient

Fractional gradient

Historical systems

Warnerke

Weston

Further reading

External links