Information about Diaphragm (optics)
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A 35mm lens set to f/8; the diameter of the seven-sided entrance pupil, the virtual image of the opening in the iris diaphragm, is 4.375mm
In optics, a diaphragm is a thin opaque structure with an opening (aperture) at its centre. The role of the diaphragm is to stop the passage of light, except for the light passing through the aperture. Thus it is also called a stop (an aperture stop, if it limits the brightness of light reaching the focal plane, or a field stop or flare stop for other uses of diaphragms in lenses). The diaphragm is placed in the light path of a lens or objective, and the size of the aperture regulates the amount of light that passes through the lens. The centre of the diaphragm's aperture coincides with the optical axis of the lens system.
Most modern cameras use a type of adjustable diaphragm known as an iris diaphragm, and often referred to simply as an iris.
See the articles on aperture and f-number for the photographic effect and system of quantification of varying the opening in the diaphragm.
Iris diaphragms versus other types
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A natural optical system that has a diaphragm and an aperture is the human eye. The iris is the diaphragm, and the opening in the iris of the eye (the pupil) is the aperture. An analogous device in a photographic lens is called an iris diaphragm.
In the early years of photography, a lens could be fitted with one of a set of interchangeable diaphragms [1], often as brass strips known as Waterhouse stops or Waterhouse diaphragms. In modern cameras, an iris diaphragm is usually used; it has an adjustable opening, like the iris of the eye. Normally, the opening is shaped in a near-round fashion by a number of movable blades. Iris diaphragms usually have five to eight blades, depending on the intended uses, pricing and quality of the device in which it is used. Furthermore, each blade can be curved, resulting in an 'inflated' pentagon (or other polygon) shape, to improve the overall roundness of the iris opening.
Some modern automatic point-and-shoot cameras have a small set of selectable fixed diaphragms, rather than an iris diaphragm (for example, the Polaroid x530 has only two apertures).
The number of blades in an iris diaphragm has a direct relation with the appearance of the blurred out-of-focus areas in an image, also called Bokeh. The more blades a diaphragm has, the rounder and less polygon-shaped the opening will be. This results in softer and more gradually blurred out-of-focus areas.
In a photograph, the number of blades that the iris diaphragm has can be guessed by counting the number of spikes converging from a light source or bright reflection. For an odd number of blades, there are twice as many spikes as there are blades.
In case of an even number of blades, the two spikes per blade will overlap each other, so the number of spikes visible will be the number of blades in the diaphragm used. This is most apparent in pictures taken in the dark with small bright spots, for example night cityscapes.
History
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Dictionary entry for Diaphragm in the 1889 Wall's Dictionary of Photography[2]
In 1762, Euler[3] says with respect to telescopes that, "it is necessary likewise to furnish the inside of the tube with one or more diaphragms, perforated with a small circular aperture, the better to exclude all extraneous light."
In 1867, Dr. Désiré van Monckhoven, in one the earliest books on photographic optics,[4] draws a distinction betweens stops and diaphragms in photography, but not in optics, saying:
- "Let us see what takes place when the stop is removed from the lens to a proper distance. In this case the stop becomes a diaphragm.
- * In optics, stop and diaphragm are synonyms. But in photographic optics they are only so by an unfortunate confusion of language. The stop reduces the lens to its central aperture; the diaphragm, on the contrary, allows all the segments of the lens to act, but only on the different radiating points placed symmetrically and concentrically in relation to the axis of the lens, or of the system of lenses (of which the axis is, besides, in every case common)."
This distinction was maintained in Wall's 1889 Dictionary of Photography (see figure), but disappeared after Ernst Abbe's theory of stops unified these concepts.
According to Rudolph Kingslake[5], the inventor of the iris diaphragm is unknown. Others credit Joseph Nicéphore Niépce for this device, around 1820. Mr. J. H. Brown, a member of the Royal Microscopical Society, appears to have invented a popular improved iris diaphragm by 1867[6].
Kingslake has more definite histories for some other diaphragm types, such as M. Noton's adjustable cat eye diaphragm of two sliding squares in 1856, and the Waterhouse stops of John Waterhouse in 1858.
References
1. ^ Louis Derr, Photography for students of physics and chemistry London: The Macmillan Co., 1906
2. ^ E. J. Wall, A Dictionary of Photography for the Amateur and Professional Photographer, New York: E. & H. T. Anthony & Co., 1889
3. ^ Leonhard Euler, "Precautions to be used in the Construction of Telescopes. Necessitiy of blackening the Inside of Tubes. Diaphragms." 1762, in Letters of Euler on different subjects in physics and philosophy. Addressed to a German princess, Vol. II, Henry Hunter, D.D. (ed.), London, 1802,
4. ^ Désiré van Monckhoven, Photographic Optics: Including the Description of Lenses and Enlarging Apparatus, English translation, London: Robert Hardwicke, 1867
5. ^ Rudolf Kingslake, A History of the Photographic Lens, London: Academic Press, 1989
6. ^ J. Henle, W, Keferstein, and G. Meissner, Bericht über die Fortschritte der Anatomie und Physiologie im Jahre 1867, Liepzip: C. F. Winter'sche Verlagshandlung, 1868.
2. ^ E. J. Wall, A Dictionary of Photography for the Amateur and Professional Photographer, New York: E. & H. T. Anthony & Co., 1889
3. ^ Leonhard Euler, "Precautions to be used in the Construction of Telescopes. Necessitiy of blackening the Inside of Tubes. Diaphragms." 1762, in Letters of Euler on different subjects in physics and philosophy. Addressed to a German princess, Vol. II, Henry Hunter, D.D. (ed.), London, 1802,
4. ^ Désiré van Monckhoven, Photographic Optics: Including the Description of Lenses and Enlarging Apparatus, English translation, London: Robert Hardwicke, 1867
5. ^ Rudolf Kingslake, A History of the Photographic Lens, London: Academic Press, 1989
6. ^ J. Henle, W, Keferstein, and G. Meissner, Bericht über die Fortschritte der Anatomie und Physiologie im Jahre 1867, Liepzip: C. F. Winter'sche Verlagshandlung, 1868.
See also
Optics (ὀπτική appearance or look in Ancient Greek) is a branch of physics that describes the behavior and properties of light and the interaction of light with matter.
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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.
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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.
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lens (or lense) is an optical device with perfect or approximate axial symmetry which transmits and refracts light, concentrating or diverging the beam. A simple lens is a lens consisting of a single optical element.
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photographic lens (also known as objective lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image
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In optics, the term optical axis is used to define a direction along which there is some degree of rotational symmetry. It can be used in several contexts:
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- In an optical system, the optical axis is an imaginary line that defines the path along which light propagates through
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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.
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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.
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In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. The following describes the iris of vertebrates, not the independently evolved iris found in some cephalopods.
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photographic lens (also known as objective lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image
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pentagon is any five-sided polygon. A pentagon may be simple or self-intersecting. The internal angles in a simple pentagon total 540°.
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Regular pentagons
The term pentagon is commonly used to mean a regular convex pentagon..... Click the link for more information.
POLYGONE is an Electronic Warfare Tactics Range located on the border between France and Germany. It is one of only two in Europe, the other being RAF Spadeadam.
The range, also referred to as the Multi-national Aircrew Electronic Warfare Tactics Facility (MAEWTF), is
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The range, also referred to as the Multi-national Aircrew Electronic Warfare Tactics Facility (MAEWTF), is
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Bokeh (from the Japanese boke ぼけ, "blur") is a photographic term referring to the appearance of out-of-focus areas in an image produced by a camera lens.
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Désiré Charles Emanuel van Monckhoven (1834–1882) was a Belgian chemist, physicist, and optician, who wrote several of the earliest books on photography and photographic optics, in French, later translated to English and other languages.
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Ernst Abbe
Ernst Karl Abbe (1840-1905)
Born January 23 1840
Eisenach, Saxe-Weimar-Eisenach
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Ernst Karl Abbe (1840-1905)
Born January 23 1840
Eisenach, Saxe-Weimar-Eisenach
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Joseph Nicéphore Niépce, also spelled Niepce (March 7, 1765 – July 5, 1833) was a French inventor, most noted as a pioneer in photography.
He began experimenting with processes to set optical images in 1793.
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Biography
Niépce was born in Chalon-sur-Saône.He began experimenting with processes to set optical images in 1793.
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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.
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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.
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shutter is a device that allows light to pass for a determined period of time, for the purpose of exposing photographic film or a light-sensitive electronic sensor to light to capture a permanent image of a scene.
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In photography, a leaf shutter is a type of camera shutter consisting of a mechanism with one or more pivoting metal leaves which normally does not allow light through the lens onto the film, but which when triggered opens the shutter by moving the leaves to uncover the lens for
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