Sensitometry
Encyclopedia
Photographic film
Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and resolution of the film...
. The study has its origins in the work by Ferdinand Hurter
Ferdinand Hurter
Ferdinand Hurter was a Swiss industrial chemist who settled in England. He also carried out research into photography.-Early life:...
and Vero Charles Driffield
Vero Charles Driffield
Vero Charles Driffield was a chemical engineer who also became involved in photographic research.Driffield was educated at Liverpool Collegiate and Sandbach Grammar School. He also attended a private school in Southport where he came into contact with a Swiss master called Dr Knecht...
(circa 1876) with early black-and-white emulsions. They determined how the density of silver produced varied with the amount of light received, and the method and time of development
Photographic developer
In the processing of photographic films, plates or papers, the photographic developer is a chemical that makes the latent image on the film or print visible. It does this by reducing the silver halides that have been exposed to light to elemental silver in the gelatine matrix...
.
Details
Plots of film density (log of opacity) versus the log of exposureExposure (photography)
In photography, exposure is the total amount of light allowed to fall on the photographic medium during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value and scene luminance over a specified area.In photographic jargon, an exposure...
are called characteristic curves, Hurter–Driffield curves, H–D curves, HD curves, H & D curves, D–logE curves, or D–logH curves. The overall shape is a bit like an "S" slanted so that its base and top are horizontal. There is usually a central region of the HD curve which approximates to a straight line, called the "linear" or "straight-line" portion; the slope of this region is called the gamma. The low end is called the "toe", and at the top, the curve rounds over to form the "shoulder".
Different commercial film materials cover a gamma range from about 0.5 to about 5. Often it is not the original film that one views but a second or later generation. In these cases the end-to-end gamma is approximately the product of the separate gammas. Photographic paper prints have end-to-end gammas generally somewhat over 1. Projection transparencies for dark surround viewing have end-to-end gamma approximately 1.5. A full set of HD curves for a film shows how these vary with developer type and time.
See also
- Film speedFilm speedFilm 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....
- DensitometryDensitometryDensitometry is the quantitative measurement of optical density in light-sensitive materials, such as photographic paper or film, due to exposure to light...
- Leon WarnerkeLeon WarnerkeLeon Warnerke . Polish engineer and inventor in the field of photography, independence activist and revolutionary. Leon Warnerke have been a pseudonym. His real name is Władysław Małachowski....
aka Władysław Małachowski, inventor of the first practical sensitometer in 1880. - Hurter and DriffieldHurter and DriffieldFerdinand Hurter and Vero Charles Driffield were nineteenth-century photographic scientists who brought quantitative scientific practice to photography through the methods of sensitometry and densitometry....
- Julius ScheinerJulius ScheinerJulius Scheiner was a German astronomer, born in Cologne and educated at Bonn. He became assistant at the astrophysical observatory in Potsdam in 1887 and its observer in chief in 1898, three years after his appointment to the chair of astrophysics in the University of Berlin...
- Scheiner sensitometer - Henry Chapman Jones - Chapman Jones plate tester
- Josef Maria EderJosef Maria EderJosef Maria Eder 16 March 1855 – 18 October 1944) was an Austrian chemist who specialized in the chemistry of photography.-Life and work:Eder was born in Krems an der Donau in 1855. He studied chemistry, physics and mathematics at the Vienna University of Technology and at the University of Vienna...
and - Eder-Hecht neutral wedge sensitometer - Spectral sensitivitySpectral sensitivitySpectral sensitivity is the relative efficiency of detection, of light or other signal, as a function of the frequency or wavelength of the signal....
- Zone systemZone systemThe Zone System is a photographic technique for determining optimal film exposure and development, formulated by Ansel Adams and Fred Archer. Adams described how the Zone System was developed: "I take this opportunity to restate that the Zone System is not an invention of mine; it is a codification...
External links
- Basic Sensitometry And Characteristics of Film (Kodak undated)http://motion.kodak.com/motion/uploadedFiles/US_plugins_acrobat_en_motion_newsletters_filmEss_06_Characteristics_of_Film.pdf
- A memorial volume containing an account of the photographic researches of Ferdinand Hurter & Vero C. Driffield ; being a reprint of their published papers, together with a history of their early work and a bibliography of later work on the same subject. (Royal Photographic Society of Great Britain 1920)