sentence-transformers/squad huggingface dataset:
Passage: 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° Sch. to 20° Sch., where an increment of 19° Sch. corresponded to a hundredfold increase in sensitivity, which meant that an increment of 3° Sch. came close to a doubling of sensitivity.

Question: Who created the Scheinergrade system?

Question: What is the Scheinergrade system used for?

Question: What do degrees Scheiner indicate?

Question: What is the range of Scheiner speeds?

Question: Approximately how many degrees indicate double the sensitivity?
Passage: 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) and Flemish-born botanist Walter Hecht (de) (1896–1960), (who, in 1919/1920, jointly developed their Eder–Hecht neutral wedge sensitometer measuring emulsion speeds in Eder–Hecht grades). Still, it remained difficult for manufactures to reliably determine film speeds, often only by comparing with competing products, 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.

Question: Who developed a device that improved on the shortcomings of Scheiner's invention?

Question: What did the Eder-Hecht device measure?

Question: What method did manufacturers use much of the time to compare film speeds?

Question: What type of measurement methods began to proliferate?

Question: What eliminated comparability?
Passage: The DIN system, officially DIN standard 4512 by Deutsches Institut für Normung (but still named Deutscher Normenausschuß (DNA) at this time), was published in January 1934. It grew out of drafts for a standardized method of sensitometry put forward by Deutscher Normenausschuß für Phototechnik as proposed by the committee for sensitometry of the Deutsche Gesellschaft für photographische Forschung since 1930 and presented by Robert Luther (de) (1868–1945) and Emanuel Goldberg (1881–1970) at the influential VIII. International Congress of Photography (German: Internationaler Kongreß für wissenschaftliche und angewandte Photographie) held in Dresden from August 3 to 8, 1931.

Question: When was the DIN system established?

Question: Who created the DIN system?

Question: What was proposed at the VIII International Congress of Photography?

Question: Who presented the idea that grew into the DIN?

Question: Where was the VIII International Congress of Photography held?
Passage: As in the Scheiner system, speeds were expressed in 'degrees'. Originally the sensitivity was written as a fraction with 'tenths' (for example "18/10° DIN"), where the resultant value 1.8 represented the relative base 10 logarithm of the speed. 'Tenths' were later abandoned with DIN 4512:1957-11, and the example above would be written as "18° DIN". The degree symbol was finally dropped with DIN 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 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" would now be labeled as "21 DIN" without emulsion changes.

Question: What unit was used in the DIN to express speeds?

Question: How was sensitivity expressed at first in the DIN system?

Question: When did the degree symbol fall out of use in the DIN system?

Question: Why did the definition of film speeds change considerably?

Question: What happened to film speeds of black-and-white negative film?
Passage: On an international level the German DIN 4512 system has been effectively superseded in the 1980s by ISO 6:1974, ISO 2240:1982, and ISO 5800:1979 where the same sensitivity is written in linear and logarithmic form as "ISO 100/21°" (now again with degree symbol). These ISO standards were subsequently adopted by DIN as well. Finally, the latest DIN 4512 revisions were replaced by corresponding ISO standards, DIN 4512-1:1993-05 by DIN ISO 6:1996-02 in September 2000, DIN 4512-4:1985-08 by DIN ISO 2240:1998-06 and DIN 4512-5:1990-11 by DIN ISO 5800:1998-06 both in July 2002.

Question: What took the place of the German DIN 4512 system?

Question: How is sensitivity shown in the ISO systems?

Question: What standards did the DIN begin to use?

Question: When were the ISO standards first adopted?

Question: When were the last ISO standards adopted?
Passage: 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 Dr. Edward Weston (1850–1936), a British-born electrical engineer, industrialist and founder of the US-based Weston Electrical Instrument Corporation, 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., who worked for them and later received a Howard N. Potts Medal for his contributions to engineering.

Question: What system was used previous to the ASA system?

Question: Who devised the Weston film speed ratings?

Question: What company did Dr. Edward Weston start?

Question: When was the Weston model 617 created?

Question: Who is credited with creating the film and meter system?
Passage: 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, 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. 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; however the changes of the ASA PH2.5-1960 revision may be taken into account when comparing with newer ASA or ISO values.

Question: Which cameras were first of their type to adopt the ASA scale?

Question: What were updated Weston values based on?

Question: How were Weston values changed to ASA values?

Question: Beginning with which year was the Weston to ASA conversion not necessary?

Question: Until what year did other models use the original Weston scale?
Passage: General Electric switched to use the ASA scale in 1946. Meters manufactured since February 1946 were 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. The company continued to publish recommended film values after that date, however, they were now aligned to the ASA scale.

Question: Which company adopted the ASA scale in 1946?

Question: Beginning what year were cameras built with the ASA meter?

Question: How did older models convert to ASA scale?

Question: How was the ASA scale shown on models built after 1946?

Question: What were recommended film values lined up with after 1946?
Passage: Based on earlier research work by Loyd Ancile Jones (1884–1954) of Kodak and inspired by the systems of Weston film speed ratings and General Electric 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 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: Exposure Index (EI).)

Question: Who pioneered research that led to the new ANSI values?

Question: What standards were the ANSI developed from?

Question: What types of film did the ANSI measure?

Question: When did the ANSI define its new measure?

Question: What were ANSI values often called in the beginning?
Passage: 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 HP3 that had been rated at 200 ASA before 1960 was labeled 400 ASA afterwards without any change to the emulsion. Similar changes were applied to the DIN system with DIN 4512:1961-10 and the BS system with BS 1380:1963 in the following years.

Question: In what year were big changes made to the ANSI?

Question: What did the 1960 changes to film speed measures lead to?

Question: Which other system were these changes applied to?

Question: In what year was the BS system modified?

Question: What safety factors were done away with beginning with the modifications to the standards?
Passage: Film speed is found from a plot of optical density vs. log of exposure for the film, known as the D–log H curve or Hurter–Driffield curve. There typically are five regions in the curve: the base + fog, the toe, the linear region, the shoulder, and the overexposed region. For black-and-white negative film, the “speed point” m is the point on the curve where density exceeds the base + fog density by 0.1 when the negative is developed so that a point n where the log of exposure is 1.3 units greater than the exposure at point m has a density 0.8 greater than the density at point m. The exposure Hm, in lux-s, is that for point m when the specified contrast condition is satisfied. The ISO arithmetic speed is determined from:

Question: What is the plot from which film speed is derived called?

Question: How many regions does the Hurter-Driffield curve have?

Question: What is plotted in the Hurter-Driffield curve?

Question: What is denoted when the specified contrast condition is met?

Question: What are the five regions of the Hurter-Driffield curve?
Passage: Film speed is used in the exposure equations 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; this increment is commonly known as a "stop". The effective f-number is proportional to the ratio between the lens focal length and aperture diameter, the diameter itself being 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.

Question: What is the effective f-number proportional to?

Question: What is used to discover the right exposure parameters?

Question: What variables help the photographer produce the desired effect?

Question: A lens with a setting of f/1.4 lets how much to hit the focal plane compared with a setting of f/2?

Question: In the APEX system, the increment that doubles the exposure is called what?
Passage: Upon exposure, the amount of light energy that reaches the film determines the effect upon the emulsion. If the brightness of the light is multiplied by a factor and the exposure of the film decreased by the same factor by varying the camera's shutter speed and aperture, so that the energy received is the same, the film will be developed to the same density. This rule is called reciprocity. The systems for determining the sensitivity for an emulsion are possible because reciprocity holds. In practice, reciprocity works reasonably well for normal photographic films for the range of exposures between 1/1000 second to 1/2 second. However, this relationship breaks down outside these limits, a phenomenon known as reciprocity failure.

Question: What determines the effect on the emulsion after exposure?

Question: In what range of exposures does reciprocity usually work?

Question: How is the exposure of film changed?

Question: How are ways of finding an emulsion's sensitivity possible?

Question: What happens outside the 1/1000 second to 1/second exposure range?
Passage: Some high-speed black-and-white films, such as Ilford Delta 3200 and Kodak T-MAX P3200, are marketed with film speeds in excess of their true ISO speed as determined using the ISO testing method. For example, the Ilford product is actually an ISO 1000 film, according to its data sheet. The manufacturers do not indicate that the 3200 number is an ISO rating on their packaging. Kodak and Fuji also marketed E6 films designed for pushing (hence the "P" prefix), such as Ektachrome P800/1600 and Fujichrome P1600, both with a base speed of ISO 400.

Question: What are two examples of films that are marketed with speeds above their true ISO speed?

Question: What speed of film is the Ilford Delta 3200?

Question: Which two companies produced E6 films meant for "pushing"?

Question: What is the base speed of Ektachrome P800/1600 and Fujichrome P1600?

Question: What type of films are Ilford Delta 3200 and Kodak T-MAX P3200?
Passage: For digital photo cameras ("digital still cameras"), an exposure index (EI) rating—commonly called ISO setting—is specified by the manufacturer such that the sRGB image files produced by the camera will have a lightness similar to what would be obtained with film of the same EI rating at the same exposure. The usual design is that the camera's parameters for interpreting the sensor data values into sRGB values are fixed, and a number of different EI choices are accommodated by varying the sensor's signal gain in the analog realm, prior to conversion to digital. Some camera designs provide at least some EI choices by adjusting the sensor's signal gain in the digital realm. A few camera designs also provide EI adjustment through a choice of lightness parameters for the interpretation of sensor data values into sRGB; this variation allows different tradeoffs between the range of highlights that can be captured and the amount of noise introduced into the shadow areas of the photo.

Question: What is another name for an exposure index rating?

Question: How do some camera designs give some EI choices?

Question: Who provides the exposure index rating?

Question: What are digital photo cameras also called?
Passage: Digital cameras have far surpassed film in terms of sensitivity to light, with ISO equivalent speeds of up to 409,600, a number that is unfathomable in the realm of conventional film photography. Faster processors, as well as advances in software noise reduction techniques allow this type of processing to be executed the moment the photo is captured, allowing photographers to store images that have a higher level of refinement and would have been prohibitively time consuming to process with earlier generations of digital camera hardware.

Question: What types of cameras have proven to be much more sensitive to light than film?

Question: What ISO equivalent speeds can digital cameras obtain?

Question: What is responsible for these vast increases in speed?

Question: What is one thing that limited speeds of older digital hardware?

Question: What does the higher speed do for the images produced?
Passage: The ISO standard ISO 12232:2006 gives digital still camera manufacturers a choice of five different techniques for determining the exposure index rating at each sensitivity setting provided by a particular camera model. Three of the techniques in ISO 12232:2006 are carried over from the 1998 version of the standard, while two new techniques allowing for measurement of JPEG output files are introduced from CIPA DC-004. Depending on the technique selected, the exposure index rating can depend on the sensor sensitivity, the sensor noise, and the appearance of the resulting image. The standard specifies the measurement of light sensitivity of the entire digital camera system and not of individual components such as digital sensors, although Kodak has reported using a variation to characterize the sensitivity of two of their sensors in 2001.

Question: How many techniques are available because of ISO 12232:2006?

Question: What techniques did CIPA DC-004 provide?

Question: What factors affect the exposure index rating?

Question: What does the standard of ISO 12232:2006 specify?

Question: In what year did Kodak start using a different way of characterizing two sensors?
Passage: The Recommended Exposure Index (REI) technique, new in the 2006 version of the standard, allows the manufacturer to specify a camera model’s EI choices arbitrarily. The choices are based solely on the manufacturer’s opinion of what EI values produce well-exposed sRGB images at the various sensor sensitivity settings. This is the only technique available under the standard for output formats that are not in the sRGB color space. This is also the only technique available under the standard when multi-zone metering (also called pattern metering) is used.

Question: What option does the Recommended Exposure Index give manufacturers?

Question: What is another name for multi-zone metering?

Question: What distinction does the Recommended Exposure Index have?

Question: When was the Recommended Exposure Index introduced?

Question: What is the only technique that can be used when multi-zone metering is used?
Passage: The Standard Output Sensitivity (SOS) technique, also new in the 2006 version of the standard, effectively specifies that the average level in the sRGB image must be 18% gray plus or minus 1/3 stop when the exposure is controlled by an automatic exposure control system calibrated per ISO 2721 and set to the EI with no exposure compensation. Because the output level is measured in the sRGB output from the camera, it is only applicable to sRGB images—typically JPEG—and not to output files in raw image format. It is not applicable when multi-zone metering is used.

Question: What year was the Standard Output Sensitivity technique introduced?

Question: What does the Standard Output Sensitivity technique apply to?

Question: What is the output level measured in?

Question: With what type of metering can the Standard Output Sensitivity not be used?

Question: With what standard is the automatic exposure control system calibrated?
Passage: The CIPA DC-004 standard requires that Japanese manufacturers of digital still cameras use either the REI or SOS techniques, and DC-008 updates the Exif specification to differentiate between these values. Consequently, the three EI techniques carried over from ISO 12232:1998 are not widely used in recent camera models (approximately 2007 and later). As those earlier techniques did not allow for measurement from images produced with lossy compression, they cannot be used at all on cameras that produce images only in JPEG format.

Question: Which methods are required by CIPA DC-004?

Question: In what year did the three EI techniques from ISO 12232:1998 largely stop being used?

Question: With what cameras can earlier techniques not be used?

Question: What nation's cameras does the CIPA DC-004 apply to?

Question: What does the DC-008 change?
Passage: where is the maximum possible exposure that does not lead to a clipped or bloomed camera output. Typically, the lower limit of the saturation speed is determined by the sensor itself, but with the gain of the amplifier between the sensor and the analog-to-digital converter, the saturation speed can be increased. The factor 78 is chosen such that exposure settings based on a standard light meter and an 18-percent reflective surface will result in an image with a grey level of 18%/√2 = 12.7% of saturation. The factor √2 indicates that there is half a stop of headroom to deal with specular reflections that would appear brighter than a 100% reflecting white surface.

Question: What does the sensor usually determine?

Question: How can the saturation speed be increased?

Question: What is indicated by the factor √2?

Question: What can too much exposure lead to?
Passage: The noise-based speed is defined as the exposure that will lead to a given signal-to-noise ratio on individual pixels. Two ratios are used, the 40:1 ("excellent image quality") and the 10:1 ("acceptable image quality") ratio. These ratios have been subjectively determined based on a resolution of 70 pixels per cm (178 DPI) when viewed at 25 cm (9.8 inch) distance. The signal-to-noise ratio is defined as the standard deviation of a weighted average of the luminance and color of individual pixels. The noise-based speed is mostly determined by the properties of the sensor and somewhat affected by the noise in the electronic gain and AD converter.

Question: Which ratios are employed to calculate noise-based speed?

Question: What is the noise-based speed?

Question: How are the two ratios found?

Question: What is a definition of signal-to-noise ratio?

Question: What factors influence the noise-based speed?
Passage: The standard specifies how speed ratings should be reported by the camera. If the noise-based speed (40:1) is higher than the saturation-based speed, the noise-based speed should be reported, rounded downwards to a standard value (e.g. 200, 250, 320, or 400). The rationale is that exposure according to the lower saturation-based speed would not result in a visibly better image. In addition, an exposure latitude can be specified, ranging from the saturation-based speed to the 10:1 noise-based speed. If the noise-based speed (40:1) is lower than the saturation-based speed, or undefined because of high noise, the saturation-based speed is specified, rounded upwards to a standard value, because using the noise-based speed would lead to overexposed images. The camera may also report the SOS-based speed (explicitly as being an SOS speed), rounded to the nearest standard speed rating.

Question: What is the range for exposure latitude?

Question: What is another speed that can also be reported by the camera?

Question: When should the noise-based speed be used?

Question: Why should noise-based speed be rounded down to a lower standard?

Question: What does the standard specify?
Passage: Despite these detailed standard definitions, cameras typically do not clearly indicate whether the user "ISO" setting refers to the noise-based speed, saturation-based speed, or the specified output sensitivity, or even some made-up number for marketing purposes. Because the 1998 version of ISO 12232 did not permit measurement of camera output that had lossy compression, it was not possible to correctly apply any of those measurements to cameras that did not produce sRGB files in an uncompressed format such as TIFF. Following the publication of CIPA DC-004 in 2006, Japanese manufacturers of digital still cameras are required to specify whether a sensitivity rating is REI or SOS.[citation needed]

Question: What measures might the user "ISO" setting correspond to?

Question: What did the 1998 version of ISO 12232 not permit?

Question: What types of sensitivity ratings can be specified by a camera?

Question: What standards changed what Japanese camera makers have to specify?

Question: In what year was CIPA DC-004 introduced?