Information about Film Speed
Film speed is the measure of a photographic film's sensitivity to light. Stock with lower sensitivity (lower ISO speed rating) requires a longer exposure and is thus called a slow film, while stock with higher sensitivity (higher ISO speed rating) can shoot the same scene with a shorter exposure and is called a fast film.
In the first approximation the amount of light energy which reaches the film determines the effect on the emulsion, so that if the brightness of the light is multiplied by a factor and the exposure of the film decreased by the same factor so that the energy received is the same, the film will be exposed to the same density; this rule is called reciprocity, and the concept of a unique speed for an emulsion is possible because reciprocity holds. In practice this holds reasonably well for normal photographic films for the range of exposures usually used, say 1/1000 sec to 1 sec, but longer exposures, different for different films, are required outside these limits, a phenomenon known as reciprocity failure.
In the ISO linear scale, which corresponds to the older ASA scale, doubling the speed of a film (that is, halving the amount of light that is necessary to expose the film) implies doubling the numeric value that designates the film speed. In the ISO logarithmic scale, which corresponds to the older DIN scale, doubling the speed of a film implies adding 3° to the numeric value that designates the film speed. For example, a film rated ISO 200/24° is twice as sensitive as a film rated ISO 100/21°.
Commonly, the logarithmic (DIN) component is omitted from film speed ratings, and only the linear component is given (e.g. "ISO 100"). In such cases, the quoted "ISO" rating is in effect synonymous with the older ASA standard.
GOST (Russian: ГОСТ) is a pre-1987 linear standard used in the former Eastern Bloc. It was almost, but not quite identical to the ASA standard. After 1987 the GOST scale was aligned to the ISO scale. GOST markings are only found on pre-1987 photographic equipment (film, cameras, lightmeters, etc.) of Eastern Bloc manufacture.
The most common ISO film ratings are 25/15°, 50/18°, 100/21°, 200/24°, 400/27°, 800/30°, 1600/33°, and 3200/36°. Consumer films are generally rated between 100/21° and 800/30°, inclusive.
A film speed is converted from the linear scale to the logarithmic scale by this formula (plus rounding to the nearest integer):
Conversion from the logarithmic scale to the linear scale is analogous, except that results must be rounded to the conventional values of the linear scale listed in the table below.
The following table shows the correspondence between these scales:
The exposure index is sometimes called the speed setting, as opposed to the speed rating.
For example, a photographer may choose to rate a 400 ISO speed film at 800 and then use push processing in order to get printable negatives from low-light conditions. In this case it is said that film has been shot at EI 800.
Another example of a situation when exposure index would differ from film manufacturer's rating is when a camera shutter is known to be miscalibrated and consistently overexposes or underexposes the film; similarly, a light meter can be known to understate or overstate lighting conditions. In such cases one could adjust EI rating accordingly in order to compensate for these effects and consistently produce correctly exposed negatives.
Film speed is roughly related to granularity, the size of the grains of silver halide in the emulsion, since larger grains give film a greater sensitivity to light. Fine-grain stock, such as portrait film or those used for the intermediate stages of copying original camera negatives, is "slow", meaning that the amount of light used to expose it must be high or the shutter must be open longer. Fast films, used for shooting in poor light or for shooting fast motion, produce a grainier image. Each grain of silver halide develops in an all-or-nothing way into dark silver or nothing. Thus, each grain is a threshold detector; in aggregate, their effect can be thought of as a noisy nonlinear analog light detector.
Kodak has defined a "Print Grain Index" (PGI) to characterize film grain (color negative films only), based on perceptual just noticeable difference of graininess in prints. They also define "granularity", a measurement of grain using an RMS measurement of density fluctuations in uniformly-exposed film, measured with a microdensitometer with 48-micron aperture.[1] Granularity varies with exposure — underexposed film looks grainier than overexposed film.
However, this standard ISO speed "rating" for a digital camera is not necessarily very related to the ISO "setting" or "exposure index" used on the camera.
The image sensors in digital cameras can be adjusted, or can have their outputs adjusted, in sensitivity to function with metering at any given ISO setting. This is usually done by simply amplifying the output of the image sensor, which increases image noise, sometimes beyond the level that the ISO standard says is acceptable.
Just as with photographic film, greater sensitivity or exposure index comes with some loss of image quality, though this loss is visible as image noise rather than grain. The best digital cameras as of 2006 exhibit no perceptible noise at ISO 200 sensitivity, and some produce usable results up to ISO 3200.
<gallery caption="Images of a flower taken at ISO 100 and ISO 1600 on a Canon 400D digital camera. Both images were shot under similar lighting conditions, varying only the ISO setting and shutter speed." widths="150px" heights="315px" perrow="5"> Image:Flower_at_100_ISO_for_comparison.JPG|ISO 100, f/5.6, 1/350 s
(click on image for larger version)
Image:Flower_at_1600_ISO_for_comparison.JPG|ISO 1600, f/5.6, 1/4000 s
(click on image for larger version)
Image:ISO_comparison_150px.jpg|Comparison of both images. This is a crop of a small section of each image displayed at 100%. The top portion was shot at 100 ISO, the bottom portion at 1600 ISO.
</gallery>
..... Click the link for more information.
In the first approximation the amount of light energy which reaches the film determines the effect on the emulsion, so that if the brightness of the light is multiplied by a factor and the exposure of the film decreased by the same factor so that the energy received is the same, the film will be exposed to the same density; this rule is called reciprocity, and the concept of a unique speed for an emulsion is possible because reciprocity holds. In practice this holds reasonably well for normal photographic films for the range of exposures usually used, say 1/1000 sec to 1 sec, but longer exposures, different for different films, are required outside these limits, a phenomenon known as reciprocity failure.
Technical information
ISO film speed scales
The standard known as ISO 5800:1987 from the International Organization for Standardization (ISO) defines both a linear scale and a logarithmic scale for measuring film speed.In the ISO linear scale, which corresponds to the older ASA scale, doubling the speed of a film (that is, halving the amount of light that is necessary to expose the film) implies doubling the numeric value that designates the film speed. In the ISO logarithmic scale, which corresponds to the older DIN scale, doubling the speed of a film implies adding 3° to the numeric value that designates the film speed. For example, a film rated ISO 200/24° is twice as sensitive as a film rated ISO 100/21°.
Commonly, the logarithmic (DIN) component is omitted from film speed ratings, and only the linear component is given (e.g. "ISO 100"). In such cases, the quoted "ISO" rating is in effect synonymous with the older ASA standard.
GOST (Russian: ГОСТ) is a pre-1987 linear standard used in the former Eastern Bloc. It was almost, but not quite identical to the ASA standard. After 1987 the GOST scale was aligned to the ISO scale. GOST markings are only found on pre-1987 photographic equipment (film, cameras, lightmeters, etc.) of Eastern Bloc manufacture.
The most common ISO film ratings are 25/15°, 50/18°, 100/21°, 200/24°, 400/27°, 800/30°, 1600/33°, and 3200/36°. Consumer films are generally rated between 100/21° and 800/30°, inclusive.
A film speed is converted from the linear scale to the logarithmic scale by this formula (plus rounding to the nearest integer):
Conversion from the logarithmic scale to the linear scale is analogous, except that results must be rounded to the conventional values of the linear scale listed in the table below.
The following table shows the correspondence between these scales:
| ISO linear scale (old ASA scale) |
ISO log scale (old DIN scale) |
GOST (Soviet pre-1987) |
Example of film stock with this nominal speed |
|---|---|---|---|
| 6 | 9° | original Kodachrome | |
| 8 | 10° | ||
| 10 | 11° | Kodachrome 8mm film | |
| 12 | 12° | 11 | Gevacolor 8mm reversal film |
| 16 | 13° | 11 | Agfacolor 8mm reversal film |
| 20 | 14° | 16 | |
| 25 | 15° | 22 | old Agfacolor, Kodachrome 25 |
| 32 | 16° | 22 | Kodak Panatomic-X |
| 40 | 17° | 32 | Kodachrome 40 (movie) |
| 50 | 18° | 45 | Fuji RVP (Velvia) |
| 64 | 19° | 45 | Kodachrome 64, Ektachrome-X |
| 80 | 20° | 65 | Ilford Commercial Ortho |
| 100 | 21° | 90 | Kodacolor Gold, Kodak T-Max (TMX) |
| 125 | 22° | 90 | Ilford FP4, Kodak Plus-X Pan |
| 160 | 23° | 130 | Fuji NPS, Kodak High-Speed Ektachrome |
| 200 | 24° | 180 | Fujicolor Superia 200 |
| 250 | 25° | 180 | |
| 320 | 26° | 250 | Kodak Tri-X Pan Professional (TXP) |
| 400 | 27° | 350 | Kodak T-Max (TMY), Tri-X 400, Ilford HP5 |
| 500 | 28° | 350 | |
| 640 | 29° | 560 | Polaroid 600 |
| 800 | 30° | 700 | Fuji NPZ |
| 1000 | 31° | 700 | Ilford Delta 3200 (see text below) |
| 1250 | 32° | ||
| 1600 | 33° | 1400–1440 | Fujicolor 1600 |
| 2000 | 34° | ||
| 2500 | 35° | ||
| 3200 | 36° | 2800–2880 | old Konica 3200 |
| 4000 | 37° | ||
| 5000 | 38° | ||
| 6400 | 39° |
Determining film speed
Film speed is found by referencing the Hurter–Driffield curve, or D–logE curve, for the film. This is a plot of optical density vs. log of exposure (lux-s). There are typically five regions in the curve: the base + fog, the toe, the linear region, the shoulder, and the overexposed region. Following the curve to the point where density exceeds the base + fog by 0.1, find the corresponding exposure. Dividing 0.8 by that exposure yields the linear ISO speed rating.Applying film speed
Film speed is used in the exposure equation to find the appropriate exposure parameters. Four variables are available to the photographer to obtain the desired effect: lighting, film speed, f-number (aperture size), and shutter speed (exposure time). The equation may be expressed as ratios, or, by taking the logarithm (base 2) of both sides, by addition, using the APEX system, in which every increment of 1 is a doubling of exposure, known as a "stop". The f-number is proportional to the ratio between the lens focal length and aperture diameter, which is proportional to the square root of the aperture area. Thus, a lens set to f/1.4 allows twice as much light to strike the focal plane as a lens set to f/2. Therefore, each f-number factor of the square root of two (approximately 1.4) is also a stop, so lenses are typically marked in that progression: f/1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc.Exposure index
Exposure index, or EI, refers to speed rating assigned to a particular film and shooting situation, and used in the exposure meter or equation, to compensate for equipment calibration inaccuracies or process variables, or to achieve certain effects. Exposure index may or may not be the same as manufacturer's film speed rating for that particular film.The exposure index is sometimes called the speed setting, as opposed to the speed rating.
For example, a photographer may choose to rate a 400 ISO speed film at 800 and then use push processing in order to get printable negatives from low-light conditions. In this case it is said that film has been shot at EI 800.
Another example of a situation when exposure index would differ from film manufacturer's rating is when a camera shutter is known to be miscalibrated and consistently overexposes or underexposes the film; similarly, a light meter can be known to understate or overstate lighting conditions. In such cases one could adjust EI rating accordingly in order to compensate for these effects and consistently produce correctly exposed negatives.
Film grain
)
Grainy high speed B/W film negative
Kodak has defined a "Print Grain Index" (PGI) to characterize film grain (color negative films only), based on perceptual just noticeable difference of graininess in prints. They also define "granularity", a measurement of grain using an RMS measurement of density fluctuations in uniformly-exposed film, measured with a microdensitometer with 48-micron aperture.[1] Granularity varies with exposure — underexposed film looks grainier than overexposed film.
Improvements in film
In the early 1980s, there were some radical improvements in film stock. It became possible to shoot color film in very low light and produce a fine-grained image with a good range of midtones.Use of grain
In advertising, music videos, and some drama, mismatches of grain, color cast, and so forth between shots are often deliberate and added in post-production.Altering film speed
Certain high-speed black-and-white films, such as Ilford Delta 3200 and Kodak T-Max P3200 (TMZ), are marketed with higher speeds on the box than their true ISO speed (determined using the ISO testing methodology). For example, the Ilford product is actually an ISO 1000 film, according to its data sheet. The manufacturers are careful not to refer to the 3200 number as an ISO speed on the packaging. These films can be successfully exposed at EI 3200 (or any of several other speeds) through the use of push processing. The most sensitive sensor common in commercial photography may be the Silicon Intensified Target vidicon, at ASA 200,000, used in TV cameras.Digital camera ISO speed and exposure index
The International Organization for Standardization (ISO) has a performance-based ISO speed standard for digital cameras, just as they have for film. ISO Standard 12232:2006 ("Photography — Digital still cameras — Determination of exposure index, ISO speed ratings, standard output sensitivity, and recommended exposure index") defines ISO speed in terms of the amount of light needed to achieve a certain "quality" in the sense of a per-pixel signal-to-noise ratio.However, this standard ISO speed "rating" for a digital camera is not necessarily very related to the ISO "setting" or "exposure index" used on the camera.
The image sensors in digital cameras can be adjusted, or can have their outputs adjusted, in sensitivity to function with metering at any given ISO setting. This is usually done by simply amplifying the output of the image sensor, which increases image noise, sometimes beyond the level that the ISO standard says is acceptable.
Just as with photographic film, greater sensitivity or exposure index comes with some loss of image quality, though this loss is visible as image noise rather than grain. The best digital cameras as of 2006 exhibit no perceptible noise at ISO 200 sensitivity, and some produce usable results up to ISO 3200.
<gallery caption="Images of a flower taken at ISO 100 and ISO 1600 on a Canon 400D digital camera. Both images were shot under similar lighting conditions, varying only the ISO setting and shutter speed." widths="150px" heights="315px" perrow="5"> Image:Flower_at_100_ISO_for_comparison.JPG|
(click on image for larger version)
(click on image for larger version)
References
- Leslie Stroebel, John Compton, Ira Current, and Richard Zakia. Basic Photographic Materials and Processes, second edition. Boston: Focal Press, 2000. ISBN 0-240-80405-8.
See also
External links
- The official ISO 5800:1987 (non-free content).
- The official ISO 12232:2006 (non-free content).
- What is the meaning of ISO for digital cameras? Digital Photography FAQ
- understanding sensitivity By Gloria Putnam
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.
..... Click the link for more information.
..... Click the link for more information.
Light is electromagnetic radiation of a wavelength that is visible to the eye (visible light). In a scientific context, the word "light" is sometimes used to refer to the entire electromagnetic spectrum.
..... Click the link for more information.
..... Click the link for more information.
exposure is the total amount of light allowed to fall on the photographic medium (photographic film or image sensor) during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance.
..... Click the link for more information.
..... Click the link for more information.
In photography and holography, reciprocity refers to the inverse relationship between the intensity and duration of light that determines exposure of light-sensitive material.
..... Click the link for more information.
..... Click the link for more information.
In photography and holography, reciprocity refers to the inverse relationship between the intensity and duration of light that determines exposure of light-sensitive material.
..... Click the link for more information.
..... Click the link for more information.
International Organization for Standardization (Organisation internationale de normalisation), widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations.
..... Click the link for more information.
..... Click the link for more information.
American National Standards Institute or ANSI (IPA pronunciation: [ænsiː]) is a private nonprofit organization that oversees the development of voluntary consensus standards for products, services, processes,
..... Click the link for more information.
..... Click the link for more information.
DIN or Din or din can have several meanings:-
..... Click the link for more information.
- A din is a loud noise.
- Dīn, an Arabic term meaning "religion" or "way of life".
- Din (Kabbalah) is one of the ten aspects of the Ein Sof in Kabbalah (more commonly known as "Gevurah").
..... Click the link for more information.
GOST refers to a set of technical standards maintained by the Euro-Asian Council for Standardization, Metrology and Certification (EASC), a regional standards organization operating under the auspices of the Commonwealth of Independent States (CIS).
..... Click the link for more information.
..... Click the link for more information.
Eastern Bloc (or Soviet Bloc) was used to refer to the Soviet Union and its allies in Central and Eastern Europe (Bulgaria, Czechoslovakia, East Germany, Hungary, Poland, Romania, and—until the early 1960s—Albania).
..... Click the link for more information.
..... Click the link for more information.
GOST refers to a set of technical standards maintained by the Euro-Asian Council for Standardization, Metrology and Certification (EASC), a regional standards organization operating under the auspices of the Commonwealth of Independent States (CIS).
..... Click the link for more information.
..... Click the link for more information.
Kodachrome
Maker: Eastman Kodak
Speed: 25/15°, 40/17°, 64/19°, 200/24°
Type: Color slide
Process: K-14 process
Format: 16mm, 8mm, 35mm
Introduced: 1935
Discontinued:
..... Click the link for more information.
Maker: Eastman Kodak
Speed: 25/15°, 40/17°, 64/19°, 200/24°
Type: Color slide
Process: K-14 process
Format: 16mm, 8mm, 35mm
Introduced: 1935
Discontinued:
..... Click the link for more information.
Kodacolor brand has been associated with various color negative films (i.e. film intended for making color prints with) since 1942.[1] Kodak claims that Kodacolor print film was the world's first true color negative film.
..... Click the link for more information.
..... Click the link for more information.
Tri-X
Maker: Kodak
Speed: 400/27°
Type: B&W print
Process: Gelatin-silver
Format: 35 mm, 120
Application: General
Tri-X Professional
Maker: Kodak
Speed: 320/26°
..... Click the link for more information.
Maker: Kodak
Speed: 400/27°
Type: B&W print
Process: Gelatin-silver
Format: 35 mm, 120
Application: General
Tri-X Professional
Maker: Kodak
Speed: 320/26°
..... Click the link for more information.
Sensitometry is the scientific study of light-sensitive materials, especially photographic film. The study has its origins in the work by Ferdinand Hurter and Vero Charles Driffield (circa 1876) with early black-and-white emulsions.
..... Click the link for more information.
..... Click the link for more information.
Not to be confused with lightning.
Lighting includes both artificial light sources such as lamps and natural illumination of interiors from daylight...... Click the link for more information.
f-number (sometimes called focal ratio, f-ratio, or relative aperture[1]) of an optical system expresses the diameter of the entrance pupil in terms of the effective focal length of the lens.
..... Click the link for more information.
..... Click the link for more information.
shutter speed is the length of time a shutter is open; the total exposure is proportional to this exposure time, or duration of light reaching the film or image sensor.
..... Click the link for more information.
..... Click the link for more information.
APEX stands for Additive system of Photographic EXposure, which was proposed in the 1960 ASA standard for monochrome film speed, ASA PH2.5-1960, as a means of simplifying exposure computation.
..... Click the link for more information.
..... Click the link for more information.
F and focal length f of a positive (convex) lens, a negative (concave) lens, a concave mirror, and a convex mirror.]] The focal length of an optical system is a measure of how strongly it converges (focuses) or diverges (diffuses) light.
..... Click the link for more information.
..... Click the link for more information.
In optics, an aperture is a hole or an opening through which light is admitted. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane.
..... Click the link for more information.
..... Click the link for more information.
f-number (sometimes called focal ratio, f-ratio, or relative aperture[1]) of an optical system expresses the diameter of the entrance pupil in terms of the effective focal length of the lens.
..... Click the link for more information.
..... Click the link for more information.
Push processing is a term from photography, referring to a development technique that increases the speed of the film being processed.
Push processing involves developing the film for longer, and/or at a higher temperature.
..... Click the link for more information.
Push processing involves developing the film for longer, and/or at a higher temperature.
..... Click the link for more information.
A light meter is a device used to measure the amount of light. In photography, a light meter is often used to determine the proper exposure for a photograph. Typically a light meter will include a computer, either digital or analogue, which allows the photographer to
..... Click the link for more information.
..... Click the link for more information.
Film grain or granularity is the random optical texture of processed photographic film due to the presence of small grains of a metallic silver developed from silver halide that have received enough photons.
..... Click the link for more information.
..... Click the link for more information.
Film grain or granularity is the random optical texture of processed photographic film due to the presence of small grains of a metallic silver developed from silver halide that have received enough photons.
..... Click the link for more information.
..... Click the link for more information.
A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide (AgBr), chloride (AgCl) and iodide (AgI). As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX.
..... Click the link for more information.
..... Click the link for more information.
emulsion is a mixture of two immiscible (unblendable) substances. One substance (the dispersed phase) is dispersed in the other (the continuous phase). Examples of emulsions include butter and margarine, espresso, mayonnaise, the photo-sensitive side of photographic film, and
..... Click the link for more information.
..... Click the link for more information.
The original camera negative (OCN) is the film in a motion picture camera which captures the original image. This is the film from which all other copies will be made. It is known as raw stock prior to exposure.
..... Click the link for more information.
..... Click the link for more information.
Eastman Kodak Company
Public NYSE: EK
Founded 1892
Headquarters Rochester, New York, USA
Key people Antonio M. Perez, Chairman & CEO
Frank S.
..... Click the link for more information.
Public NYSE: EK
Founded 1892
Headquarters Rochester, New York, USA
Key people Antonio M. Perez, Chairman & CEO
Frank S.
..... Click the link for more information.
This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.
Herod_Archelaus
