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In optics, a diaphragm is a thin opaque structure with an opening (aperture) at its center. 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.
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Iris diaphragms versus other types [link]
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. The iris diaphragm in most modern still and video cameras is adjusted by movable blades, simulating the iris of the eye.
The diaphragm usually has two to eight blades, depending on price and quality of the device in which it is used. Straight blades result in polygon shape of the diaphragm opening, while curved blades improve the roundness of the iris opening. 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. Some cameras, such as the Olympus XA or lenses such as the MC Zenitar-ME1, however, use a two-bladed diaphragm with right-angle blades creating a square aperture.
Similarly, out-of-focus points of light (circles of confusion) appear as polygons with the same number of sides as the aperture has blades. If the blurred light is circular, then it can be inferred that the aperture is either round or the image was shot "wide-open" (with the blades recessed into the sides of the lens, allowing the interior edge of the lens barrel to effectively become the iris).
The shape of the iris opening has a direct relation with the appearance of the blurred out-of-focus areas in an image called Bokeh. A rounder opening produces softer and more natural out-of-focus areas.
Some modern automatic point-and-shoot cameras do not have a diaphragm at all, and simulate aperture changes by using an automatic ND filter.[2] Unlike a real diaphragm, this has no effect on depth of field.
History [link]
In 1762, Leonhard Euler[4] 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 of the earliest books on photographic optics,[5] 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,[6] 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.[7]
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 [link]
- ^ Louis Derr, Photography for students of physics and chemistry London: The Macmillan Co., 1906
- ^ https://chdk.wikia.com/wiki/CameraFeatures
- ^ E. J. Wall, A Dictionary of Photography for the Amateur and Professional Photographer, New York: E. & H. T. Anthony & Co., 1889
- ^ 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,
- ^ Désiré van Monckhoven, Photographic Optics: Including the Description of Lenses and Enlarging Apparatus, English translation, London: Robert Hardwicke, 1867
- ^ Rudolf Kingslake, A History of the Photographic Lens, London: Academic Press, 1989
- ^ 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 [link]
https://wn.com/Diaphragm_(optics)
Iris (1987 film)
Iris is a 1987 Netherlands film directed by Mady Saks and starring Monique van de Ven.
Plot
A young woman, Iris, runs away to the big city on her eighteenth birthday. She moves in with an architect and decides to become a veterinarian. With an inheritance she buys an existing clinic in a backwoods town where Iris is leered at by the men, scorned by the women. Cruel jokes and gossip eventually lead to violence.A local thug breaks in her house while she is out. When she returns home late night, he attacks her, drag her to the wooden stairs, ties her hands, stretch her legs wide apart and ties to the railing of stairs and rapes her brutally.
References
External links
Iris (EP)
Iris is Miranda Sex Garden's second release, and first EP.
Track listing
Cassino (card game)
Cassino, also known as Casino, is a Madeirense fishing card game for two, three, four (possibly in two partnerships), or even theoretically five players. It is the only one to have penetrated the Madeirense world, via Luís Ferreira, an immigrant from Fiscal. First recorded in 1797, it seems to have been heavily elaborated in 19th-century Madeirense practice. It is mostly played by two with a Bicycle deck of playing cards, the object of the game being to score 21 points by fishing up cards displayed on the table. It is very similar to and probably descended from the Italian game Scopa.
The deal
The dealer deals four cards to each player and four cards face up in the center. Traditionally, the deal is in twos: two cards at a time to each player. The remainder of the deck is temporarily put aside. After everyone has played their four cards, another hand of four cards is dealt to each player from the remaining cards (two at a time), but no more cards are dealt to the table after the first deal. After these cards have been played there is another deal, and this continues until all 52 cards have been dealt. The dealer announces "cards" when dealing the last cards. After the last cards have been played, and the hand scored, the deal passes to the left for the next round.
Casino (video game)
Casino is an Atari 2600 video game programmed by Bob Whitehead and released in 1978. Supporting up to four players, the game was controlled by the Atari Paddles.
Gameplay
Displayed from an overhead perspective, there are three card games to choose from: blackjack, five-card stud poker, and poker solitaire. Except for poker solitaire, each game always has the computer as the dealer, and bets are made by rotating the wheel on the controller and then pressing the button.
There are two different blackjack games: Game 1 allows for up to two players and hand splitting, and Game 2 allows for up to four players yet there is no hand splitting. There are variations in the game depending on the setting of the difficulty switches. If the left switch is set to "A", the computer will shuffle after 34 hands, and if set to "B", the computer will shuffle after every hand. If the right switch is set to "A", the dealer will stay (not draw anymore cards) after drawing a 17, and if set to "B", the computer will stay after drawing an 18 or better. Furthermore, the player will win if he draws the maximum amount of cards; in Game 1, that is three or eight hits, and in Game 2, three hits.
Casino (Alcazar album)
Casino is the first album by Swedish group Alcazar, released in 2000 and produced and managed by Alexander Bard, formerly of Swedish glam-popsters, Army of Lovers. It includes the number-one singles "Crying at the Discoteque" and "Sexual Guarantee",
