1.
Focus (optics)
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In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent and this non-ideal focusing may be caused by aberrations of the imaging optics. In the absence of significant aberrations, the smallest possible blur circle is the Airy disc, aberrations tend to get worse as the aperture diameter increases, while the Airy circle is smallest for large apertures. An image, or image point or region, is in focus if light from object points is converged almost as much as possible in the image, the border between these is sometimes defined using a circle of confusion criterion. A principal focus or focal point is a focus, For a lens, or a spherical or parabolic mirror. Since light can pass through a lens in either direction, a lens has two focal points—one on each side, the distance in air from the lens or mirrors principal plane to the focus is called the focal length. Elliptical mirrors have two points, light that passes through one of these before striking the mirror is reflected such that it passes through the other. The focus of a mirror is either of two points which have the property that light from one is reflected as if it came from the other. Diverging lenses and convex mirrors do not focus a beam to a point. Instead, the focus is the point from which the light appears to be emanating, a convex elliptical mirror will reflect light directed towards one focus as if it were radiating from the other focus, both of which are behind the mirror. A convex hyperbolic mirror will reflect rays emanating from the point in front of the mirror as if they were emanating from the focal point behind the mirror. Conversely, it can focus rays directed at the point that is behind the mirror towards the focal point that is in front of the mirror as in a Cassegrain telescope. Autofocus Cardinal point Defocus aberration Depth of field Depth of focus Far point Focus Fixed focus Bokeh Focus stacking Focal Plane
2.
Ray (optics)
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In optics a ray is an idealized model of light, obtained by choosing a line that is perpendicular to the wavefronts of the actual light, and that points in the direction of energy flow. This allows even very complex systems to be analyzed mathematically or simulated by computer. Ray theory does not describe phenomena such as interference and diffraction, a light ray is a line that is perpendicular to the lights wavefronts, its tangent is collinear with the wave vector. Light rays in homogeneous media are straight and they bend at the interface between two dissimilar media and may be curved in a medium in which the refractive index changes. Geometric optics describes how rays propagate through an optical system, objects to be imaged are treated as collections of independent point sources, each producing spherical wavefronts and corresponding outward rays. Rays from each point can be mathematically propagated to locate the corresponding point on the image. There are many special rays that are used in modelling to analyze an optical system. These are defined and described below, grouped by the type of system they are used to model, an incident ray is a ray of light that strikes a surface. The angle between this ray and the perpendicular or normal to the surface is the angle of incidence, the reflected ray corresponding to a given incident ray, is the ray that represents the light reflected by the surface. The angle between the normal and the reflected ray is known as the angle of reflection. The Law of Reflection says that for a surface, the angle of reflection always equals the angle of incidence. The refracted ray or transmitted ray corresponding to an incident ray represents the light that is transmitted through the surface. The angle between this ray and the normal is known as the angle of refraction, and it is given by Snells Law. Conservation of energy requires that the power in the incident ray must equal the sum of the power in the ray, the power in the reflected ray. If the material is birefringent, the ray may split into ordinary and extraordinary rays. A meridional ray or tangential ray is a ray that is confined to the containing the systems optical axis. A skew ray is a ray that does not propagate in a plane that contains both the point and the optical axis. Such rays do not cross the optical axis anywhere, and are not parallel to it
3.
Real image
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In optics, a real image is an image which is located in the plane of convergence for the light rays that originate from a given object. If a screen is placed in the plane of an image the image will generally become visible on the screen. Examples of real images include the image seen on a screen, the image produced on a detector in the rear of a camera. In ray diagrams, real rays of light are represented by full, solid lines. A real image occurs where rays converge, whereas a virtual image occurs where rays only appear to converge. Real images can be produced by concave mirrors and converging lenses, only if the object is placed away from the mirror/lens than the focal point. As the object approaches the point the image is approaching infinity. Virtual image Focal plane Image plane Lens
4.
Lens (optics)
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A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a piece of transparent material, while a compound lens consists of several simple lenses. Lenses are made from such as glass or plastic, and are ground. A lens can focus light to form an image, unlike a prism, devices that similarly focus or disperse waves and radiation other than visible light are also called lenses, such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses. The word lens comes from the Latin name of the lentil, the genus of the lentil plant is Lens, and the most commonly eaten species is Lens culinaris. The lentil plant also gives its name to a geometric figure, the variant spelling lense is sometimes seen. While it is listed as a spelling in some dictionaries. The oldest lens artifact is the Nimrud lens, dating back 2700 years to ancient Assyria, david Brewster proposed that it may have been used as a magnifying glass, or as a burning-glass to start fires by concentrating sunlight. Another early reference to magnification dates back to ancient Egyptian hieroglyphs in the 8th century BC, the earliest written records of lenses date to Ancient Greece, with Aristophanes play The Clouds mentioning a burning-glass. Some scholars argue that the evidence indicates that there was widespread use of lenses in antiquity. Such lenses were used by artisans for fine work, and for authenticating seal impressions, both Pliny and Seneca the Younger described the magnifying effect of a glass globe filled with water. The Viking lenses were capable of concentrating enough sunlight to ignite fires, between the 11th and 13th century reading stones were invented. Often used by monks to assist in illuminating manuscripts, these were primitive plano-convex lenses initially made by cutting a sphere in half. As the stones were experimented with, it was understood that shallower lenses magnified more effectively. Lenses came into use in Europe with the invention of spectacles. Spectacle makers created improved types of lenses for the correction of vision based more on knowledge gained from observing the effects of the lenses. With the invention of the telescope and microscope there was a deal of experimentation with lens shapes in the 17th. Opticians tried to construct lenses of varying forms of curvature, wrongly assuming errors arose from defects in the figure of their surfaces
5.
Mirror
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This is different from other light-reflecting objects that do not preserve much of the original wave signal other than color and diffuse reflected light. The most familiar type of mirror is the mirror, which has a flat screen surface. Curved mirrors are used, to produce magnified or diminished images or focus light or simply distort the reflected image. Mirrors are commonly used for personal grooming or admiring oneself, decoration, Mirrors are also used in scientific apparatus such as telescopes and lasers, cameras, and industrial machinery. Most mirrors are designed for light, however, mirrors designed for other wavelengths of electromagnetic radiation are also used. The first mirrors used by people were most likely pools of dark, still water, the requirements for making a good mirror are a surface with a very high degree of flatness, and a surface roughness smaller than the wavelength of the light. The earliest manufactured mirrors were pieces of polished stone such as obsidian, examples of obsidian mirrors found in Anatolia have been dated to around 6000 BC. Mirrors of polished copper were crafted in Mesopotamia from 4000 BC, polished stone mirrors from Central and South America date from around 2000 BC onwards. In China, bronze mirrors were manufactured from around 2000 BC, some of the earliest bronze, Mirrors made of other metal mixtures such as copper and tin speculum metal may have also been produced in China and India. Mirrors of speculum metal or any precious metal were hard to produce and were owned by the wealthy. Stone mirrors often had poor reflectivity compared to metals, yet metals scratch or tarnish easily, depending upon the color, both often yielded reflections with poor color rendering. The poor image quality of ancient mirrors explains 1 Corinthians 13s reference to seeing as in a mirror, glass was a desirable material for mirrors. Because the surface of glass is smooth, it produces reflections with very little blur. In addition, glass is very hard and scratch resistant, however, glass by itself has little reflectivity, so people began coating it with metals to increase the reflectivity. According to Pliny, the people of Sidon developed a technique for creating crude mirrors by coating glass with molten lead. Glass mirrors backed with gold leaf are mentioned by Pliny in his Natural History and these circular mirrors were typically small, from only a fraction of an inch to as much as eight inches in diameter. These small mirrors produced distorted images, yet were prized objects of high value and these ancient glass mirrors were very thin, thus very fragile, because the glass needed to be extremely thin to prevent cracking when coated with a hot, molten metal. Due to the quality, high cost, and small size of these ancient glass mirrors
6.
Microscope
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A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy, microscopic means invisible to the eye unless aided by a microscope. There are many types of microscopes, the most common is the optical microscope, which uses light to image the sample. Other major types of microscopes are the microscope, the ultramicroscope. The earliest microscopes were single lens magnifying glasses with limited magnification which date at least as far back as the wide use of lenses in eyeglasses in the 13th century. Compound microscopes, which combine an objective lens with an eyepiece to view a real image, the actual inventor of the compound microscope is unknown although many claims have been made over the years. These include what may be a claim by the son of Zacharias Janssen that his father invented the microscope and telescope as early as 1590. Historians note the compound microscope did not appear in the Netherlands until the 1620s, giovanni Faber coined the name microscope for the compound microscope Galileo submitted to the Accademia dei Lincei in 1625. The first detailed account of the construction of living tissue based on the use of a microscope did not appear until 1644, in Giambattista Odiernas Locchio della mosca. It was not until the 1660s and 1670s that the microscope was used extensively for research in Italy, marcello Malpighi in Italy began the analysis of biological structures, beginning with the lungs. Robert Hookes Micrographia had an impact, largely because of its impressive illustrations. A significant contribution came from Antonie van Leeuwenhoek who achieved up to 300 times magnification using a single lens microscope. He sandwiched a very small glass ball lens between the holes in two metal plates riveted together, and with a needle attached to mount the specimen. Then, Van Leeuwenhoek re-discovered red blood cells and spermatozoa, on 9 October 1676, he reported the discovery of micro-organisms. The performance of light microscopy depends as much on how the sample is illuminated as on how it is observed, early instruments were limited until this principle was fully appreciated and developed, and until electric lamps were available as light sources. In 1893 August Köhler developed a key principle of sample illumination, Köhler illumination and this method of sample illumination produces even lighting and overcomes the limited contrast and resolution imposed by early techniques of sample illumination. In the early 20th century a significant alternative to light microscopy was developed, ernst Ruska started development of the first electron microscope in 1931 which was the transmission electron microscope. The transmission electron microscope works on the principle as an optical microscope but uses electrons in the place of light
7.
Telescope
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A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation. The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s and they found use in both terrestrial applications and astronomy. Within a few decades, the telescope was invented, which used mirrors to collect. In the 20th century many new types of telescopes were invented, including radio telescopes in the 1930s, the word telescope now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors. The word telescope was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galileis instruments presented at a banquet at the Accademia dei Lincei, in the Starry Messenger, Galileo had used the term perspicillum. The earliest recorded working telescopes were the telescopes that appeared in the Netherlands in 1608. Their development is credited to three individuals, Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, Galileo heard about the Dutch telescope in June 1609, built his own within a month, and improved upon the design in the following year. Also in 1609, Thomas Harriot became the first person known to point a telescope skyward in order to make observations of a celestial object. The idea that the objective, or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using parabolic mirrors—reduction of spherical aberration and no chromatic aberration—led to many proposed designs, in 1668, Isaac Newton built the first practical reflecting telescope, of a design which now bears his name, the Newtonian reflector. The invention of the lens in 1733 partially corrected color aberrations present in the simple lens and enabled the construction of shorter. The largest reflecting telescopes currently have objectives larger than 10 m, the 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays. The first purpose built radio telescope went into operation in 1937, since then, a tremendous variety of complex astronomical instruments have been developed. The name telescope covers a range of instruments. Most detect electromagnetic radiation, but there are differences in how astronomers must go about collecting light in different frequency bands. The near-infrared can be collected much like light, however in the far-infrared and submillimetre range. For example, the James Clerk Maxwell Telescope observes from wavelengths from 3 μm to 2000 μm, on the other hand, the Spitzer Space Telescope, observing from about 3 μm to 180 μm uses a mirror. Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe in the range from about 0.2 μm to 1.7 μm
8.
Camera
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Thumb|A2016 Nikon D810 A camera is an optical instrument for recording or capturing images, which may be stored locally, transmitted to another location, or both. The images may be individual still photographs or sequences of images constituting videos or movies, the camera is a remote sensing device as it senses subjects without physical contact. The word camera comes from camera obscura, which means dark chamber and is the Latin name of the device for projecting an image of external reality onto a flat surface. The modern photographic camera evolved from the camera obscura, the functioning of the camera is very similar to the functioning of the human eye. A camera may work with the light of the spectrum or with other portions of the electromagnetic spectrum. A still camera is a device which creates a single image of an object or scene. All cameras use the basic design, light enters an enclosed box through a converging lens/convex lens. A shutter mechanism controls the length of time that light can enter the camera, a display, often a liquid crystal display, permits the user to view scene to be recorded and settings such as ISO speed, exposure, and shutter speed. A movie camera or a video camera operates similarly to a camera, except it records a series of static images in rapid succession. When the images are combined and displayed in order, the illusion of motion is achieved, the forerunner to the photographic camera was the camera obscura. The oldest known record of this principle is a description by Han Chinese philosopher Mozi, Mozi correctly asserted that the camera obscura image is inverted because light travels in straight lines from its source. In the 11th century Arab physicist Ibn al-Haytham s wrote very influential essays about experiments with light through an opening in a darkened room. The use of a lens in the opening of a wall or closed window shutter of a room to project images used as a drawing aid has been traced back to circa 1550. Since the late 17th century portable camera obscura devices in tents, before the development of the photographic camera, it had been known for hundreds of years that some substances, such as silver salts, darkened when exposed to sunlight. The first person to use this chemistry to create images was Thomas Wedgwood, to create images, Wedgwood placed items, such as leaves and insect wings, on ceramic pots coated with silver nitrate, and exposed the set-up to light. These images werent permanent, however, as Wedgwood didnt employ a fixing mechanism and he ultimately failed at his goal of using the process to create fixed images created by a camera obscura. The first permanent photograph of an image was made in 1826 by Joseph Nicéphore Niépce using a sliding wooden box camera made by Charles. Niépce had been experimenting with ways to fix the images of a camera obscura since 1816, the photograph Niépce succeeded in creating shows the view from his window
9.
Slide projector
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A slide projector is an opto-mechanical device for showing photographic slides. Slide projectors were widely used in educational and other institutional settings. This glass transmits visible wavelengths but absorbs infrared, light passes through the transparent slide and lens, and the resulting image is enlarged and projected onto a perpendicular flat screen so the audience can view its reflection. Alternatively, the image may be projected onto a translucent rear projection screen, often used for continuous automatic display for close viewing and this form of projection also avoids the audience interrupting the light stream by casting their shadows on the projection or by bumping into the projector. Slide projectors get smarter all the time
10.
CD player
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A CD player is an electronic device that plays audio compact discs, which are a digital optical disc data storage format. CD players were first sold to consumers in 1982, CDs typically contain recordings of audio material such as music. CD players are often a part of home systems, car audio systems. With the exception of CD boomboxes, most CD players do not produce sound by themselves, most CD players only produce an output signal via a headphone jack and/or RCA jacks. To listen to using a CD player with a headphone output jack. To use a CD player in a stereo system, the user connects an RCA cable to the RCA jacks or other outputs and connects it to a hi-fi. They are also manufactured as portable devices, which are battery powered, modern units can play other formats in addition to PCM audio coding used in CDs, such as MP3, AAC and WMA. DJs playing dance music at clubs often use specialized players with a playback speed to alter the pitch. Audio engineers using CD players to play music for an event through a reinforcement system use professional audio-grade CD players. CD playback functionality is also valuable on CD-ROM/DVD-ROM drive equipped computers as well as on DVD players, American inventor James T. Russell has been credited with inventing the first system to record digital information on an optical transparent foil that is lit from behind by a high-power halogen lamp. Russells patent application was first filed in 1966, and he was granted a patent in 1970, following litigation, Sony and Philips licensed Russells patents in the 1980s. The Compact Disc is an evolution of LaserDisc technology, where a laser beam is used that enables the high information density required for high-quality digital audio signals. Prototypes were developed by Philips and Sony independently in the late 1970s, in 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. After a year of experimentation and discussion, the Red Book CD-DA standard was published in 1980, after their commercial release in 1982, compact discs and their players were extremely popular. Despite costing up to $1,000, over 400,000 CD players were sold in the United States between 1983 and 1984. The success of the disc has been credited to the cooperation between Philips and Sony, who came together to agree upon and develop compatible hardware. The unified design of the disc allowed consumers to purchase any disc or player from any company. In 1974, L. However, due to the performance of the analog format
11.
Magnifying glass
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A magnifying glass is a convex lens that is used to produce a magnified image of an object. The lens is mounted in a frame with a handle. A sheet magnifier consists of very narrow concentric ring-shaped lenses. This arrangement is known as a Fresnel lens, a magnifying glass can also be used to focus light, such as to concentrate the suns radiation to create a hot spot at the focus for fire starting. The magnifying glass is an icon of detective fiction, particularly that of Sherlock Holmes, roger Bacon described the properties of a magnifying glass in 13th-century England. Eyeglasses were developed in 13th-century Italy, the magnification of a magnifying glass depends upon where it is placed between the users eye and the object being viewed, and the total distance between them. The magnifying power is equivalent to angular magnification, the magnifying power is the ratio of the sizes of the images formed on the users retina with and without the lens. For the without case, it is assumed that the user would bring the object as close to one eye as possible without it becoming blurry. This point, known as the point, varies with age. In a young child, it can be as close as 5 cm, while, magnifiers are typically characterized using a standard value of 0.25 m. The highest magnifying power is obtained by putting the lens very close to one eye and moving the eye, the object will then typically also be close to the lens. The magnifying power obtained in this condition is MP0 = Φ +1, where Φ is the power in dioptres. This value of the power is the one normally used to characterize magnifiers. It is typically denoted m×, where m = MP0 and this is sometimes called the total power of the magnifier. However, magnifiers are not always used as described above because it is comfortable to put the magnifier close to the object. The eye can then be a distance away, and a good image can be obtained very easily. The magnifying power in case is roughly MP = Φ. A typical magnifying glass might have a length of 25 cm
12.
Focal length
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The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. A system with a focal length has greater optical power than one with a long focal length. For a thin lens in air, the length is the distance from the center of the lens to the principal foci of the lens. For a converging lens, the length is positive, and is the distance at which a beam of collimated light will be focused to a single spot. For a diverging lens, the length is negative, and is the distance to the point from which a collimated beam appears to be diverging after passing through the lens. The focal length of a lens can be easily measured by using it to form an image of a distant light source on a screen. The lens is moved until an image is formed on the screen. In this case 1/u is negligible, and the length is then given by f ≈ v. Back focal length or back focal distance is the distance from the vertex of the last optical surface of the system to the focal point. For an optical system in air, the focal length gives the distance from the front. If the surrounding medium is not air, then the distance is multiplied by the index of the medium. Some authors call these distances the front/rear focal lengths, distinguishing them from the front/rear focal distances, defined above. In general, the length or EFL is the value that describes the ability of the optical system to focus light. The other parameters are used in determining where an image will be formed for an object position. The quantity 1/f is also known as the power of the lens. The corresponding front focal distance is, FFD = f, in the sign convention used here, the value of R1 will be positive if the first lens surface is convex, and negative if it is concave. The value of R2 is negative if the surface is convex
13.
Magnification
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Magnification is the process of enlarging something only in appearance, not in physical size. This enlargement is quantified by a number also called magnification. When this number is less one, it refers to a reduction in size. Typically, magnification is related to scaling up visuals or images to be able to see detail, increasing resolution, using microscope, printing techniques. In all cases, the magnification of the image does not change the perspective of the image, some optical instruments provide visual aid by magnifying small or distant subjects. A magnifying glass, which uses a lens to make things look bigger by allowing the user to hold them closer to their eye. A microscope, which makes an object appear as a much larger image at a comfortable distance for viewing. A microscope is similar in layout to a telescope except that the object being viewed is close to the objective, a slide projector, which projects a large image of a small slide on a screen. Optical magnification is the ratio between the apparent size of an object and its size, and thus it is a dimensionless number. Optical magnification is sometimes referred to as power, although this can lead to confusion with optical power, for real images, such as images projected on a screen, size means a linear dimension. For optical instruments with an eyepiece, the dimension of the image seen in the eyepiece cannot be given. Strictly speaking, one should take the tangent of that angle, example, The angular size of the full moon is 0. 5°. In binoculars with 10x magnification it appears to subtend an angle of 5°, the linear magnification of a thin lens is where f is the focal length and d o is the distance from the lens to the object. Note that for real images, M is negative and the image is inverted, for virtual images, M is positive and the image is upright. The image recorded by a film or image sensor is always a real image and is usually inverted. When measuring the height of an image using the cartesian sign convention the value for hi will be negative. However, the sign convention used in photography is real is positive. Therefore in photography, Object height and distance are always real, when the focal length is positive the images height, distance and magnification are real and positive
14.
Numerical aperture
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In optics, the numerical aperture of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light. The exact definition of the term varies slightly between different areas of optics, in general, this is the angle of the real marginal ray in the system. Because the index of refraction is included, the NA of a pencil of rays is an invariant as a pencil of rays passes from one material to another through a flat surface. This is easily shown by rearranging Snells law to find that n sin θ is constant across an interface, in air, the angular aperture of the lens is approximately twice this value. The NA is generally measured with respect to an object or image point. In microscopy, NA generally refers to object-space NA unless otherwise noted, in microscopy, NA is important because it indicates the resolving power of a lens. The size of the finest detail that can be resolved is proportional to λ/2NA, a lens with a larger numerical aperture will be able to visualize finer details than a lens with a smaller numerical aperture. Assuming quality optics, lenses with larger numerical apertures collect more light and will provide a brighter image. Numerical aperture is used to define the pit size in optical disc formats, increasing the magnification and the numerical aperture of the objective reduces the working distance, i. e. the distance between front lens and specimen. Numerical aperture is not typically used in photography. Instead, the aperture of a lens is expressed by the f-number, written f/ or N. This ratio is related to the numerical aperture when the lens is focused at infinity. Based on the diagram at the right, the numerical aperture of the lens is, NA i = n sin θ = n sin ≈ n D2 f, thus N ≈ 1/2NAi. As Rudolf Kingslake explains, It is an error to suppose that the ratio is actually equal to tan θ. The tangent would, of course, be if the principal planes were really plane. In this sense, the traditional definition and illustration of f-number is misleading. The f-number describes the ability of the lens in the case where the marginal rays on the object side are parallel to the axis of the lens. This case is encountered in photography, where objects being photographed are often far from the camera
15.
Eyepiece
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An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is so named because it is usually the lens that is closest to the eye when someone looks through the device, the objective lens or mirror collects light and brings it to focus creating an image. The eyepiece is placed near the point of the objective to magnify this image. The amount of magnification depends on the length of the eyepiece. An eyepiece consists of several elements in a housing, with a barrel on one end. The barrel is shaped to fit in an opening of the instrument to which it is attached. The image can be focused by moving the eyepiece nearer and further from the objective, most instruments have a focusing mechanism to allow movement of the shaft in which the eyepiece is mounted, without needing to manipulate the eyepiece directly. The eyepieces of binoculars are usually mounted in the binoculars, causing them to have a pre-determined magnification. With telescopes and microscopes, however, eyepieces are usually interchangeable, by switching the eyepiece, the user can adjust what is viewed. For instance, eyepieces will often be interchanged to increase or decrease the magnification of a telescope, eyepieces also offer varying fields of view, and differing degrees of eye relief for the person who looks through them. Several properties of an eyepiece are likely to be of interest to a user of an optical instrument, eyepieces are optical systems where the entrance pupil is invariably located outside of the system. They must be designed for optimal performance for a distance to this entrance pupil. In a refracting astronomical telescope the entrance pupil is identical with the objective and this may be several feet distant from the eyepiece, whereas with a microscope eyepiece the entrance pupil is close to the back focal plane of the objective, mere inches from the eyepiece. Microscope eyepieces may be corrected differently from telescope eyepieces, however, elements are the individual lenses, which may come as simple lenses or singlets and cemented doublets or triplets. When lenses are cemented together in pairs or triples, the elements are called groups. The first eyepieces had only a lens element, which delivered highly distorted images. Two and three-element designs were invented soon after, and quickly became standard due to the image quality. Today, engineers assisted by computer-aided drafting software have designed eyepieces with seven or eight elements that deliver exceptionally large, internal reflections, sometimes called scatter, cause the light passing through an eyepiece to disperse and reduce the contrast of the image projected by the eyepiece
16.
Oil immersion
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In light microscopy, oil immersion is a technique used to increase the resolving power of a microscope. This is achieved by immersing both the lens and the specimen in a transparent oil of high refractive index, thereby increasing the numerical aperture of the objective lens. Immersion oils are transparent oils that have specific optical and viscosity characteristics necessary for use in microscopy, typical oils used have an index of refraction around 1.515. An oil immersion objective is an objective lens specially designed to be used in this way, many condensers also give optimal resolution when the condenser lens is immersed in oil. Lenses reconstruct the light scattered by an object, to successfully achieve this end, ideally, all the diffraction orders have to be collected. This is related to the angle of the lens and its refractive index. The resolution of a microscope is defined as the minimum separation needed between two objects under examination in order for the microscope to discern them as separate objects and this minimum distance is labelled δ. If two objects are separated by a shorter than δ, they will appear as a single object in the microscope. A measure of the power, R. P. of a lens is given by its numerical aperture, NA. From this it is clear that a resolution is connected with a high numerical aperture. State of the art objectives can have an aperture of up to 0.95. Because sin α0 is always less than or equal to unity, if the space between the objective lens and the specimen is filled with oil however, the numerical aperture can obtain values greater than unity. This is because oil has a refractive index greater than 1, from the above it is understood that oil between the specimen and the objective lens improves the resolving power by a factor 1/n. Objectives specifically designed for this purpose are known as oil immersion objectives, Oil immersion objectives are used only at very large magnifications that require high resolving power. Objectives with high power magnification have short focal lengths, facilitating the use of oil, the oil is applied to the specimen, and the stage is raised, immersing the objective in oil. The refractive indices of the oil and of the glass in the first lens element are nearly the same, the correct immersion oil for an objective lens has to be used to ensure that the refractive indices are correctly matched. Use of an oil immersion lens with the incorrect immersion oil, or without immersion oil altogether, the strength of this effect depends on the size of the refractive index mismatch. Oil immersion can generally only be used on rigidly mounted specimens otherwise the surface tension of the oil can move the coverslip and this can also happen on inverted microscopes because the coverslip is below the slide
17.
Camera lens
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A lens might be permanently fixed to a camera, or it might be interchangeable with lenses of different focal lengths, apertures, and other properties. While in principle a simple convex lens will suffice, in practice a compound made up of a number of optical lens elements is required to correct the many optical aberrations that arise. Some aberrations will be present in any lens system and it is the job of the lens designer to balance these and produce a design that is suitable for photographic use and possibly mass production. Typical rectilinear lenses can be thought of as improved pinhole lenses, as shown, a pinhole lens is simply a small aperture that blocks most rays of light, ideally selecting one ray to the object for each point on the image sensor. Here a pixel is the area of the detector exposed to light from a point on the object, making the pinhole smaller improves resolution, but reduces the amount of light captured. At a certain point, shrinking the hole does not improve the resolution because of the diffraction limit, beyond this limit, making the hole smaller makes the image blurrier as well as darker. Practical lenses can be thought of as an answer to the question how can a pinhole lens be modified to more light. A first step is to put a simple convex lens at the pinhole with a length equal to the distance to the film plane. The geometry is almost the same as with a pinhole lens. From the front of the camera, the hole, would be seen. If one were inside the camera, one would see the acting as a projector. The virtual image of the aperture from inside the camera is the exit pupil. Practical photographic lenses include more lens elements, a camera lens may be made from a number of elements, from one, as in the Box Brownies meniscus lens, to over 20 in the more complex zooms. These elements may themselves comprise a group of lenses cemented together, the front element is critical to the performance of the whole assembly. In all modern lenses the surface is coated to reduce abrasion, flare, and surface reflectance, to minimize aberration, the curvature is usually set so that the angle of incidence and the angle of refraction are equal. In a prime lens this is easy, but in a zoom there is always a compromise, the lens usually is focused by adjusting the distance from the lens assembly to the image plane, or by moving elements of the lens assembly. To improve performance, some lenses have a cam system that adjusts the distance between the groups as the lens is focused, manufacturers call this different things, Nikon calls it CRC, Canon calls it a floating system, and Hasselblad and Mamiya call it FLE. Glass is the most common used to construct lens elements, due to its good optical properties
18.
Optical aberration
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An optical aberration is a departure of the performance of an optical system from the predictions of paraxial optics. In an imaging system, it occurs when light from one point of an object does not converge into a point after transmission through the system. Aberrations occur because the simple theory is not a completely accurate model of the effect of an optical system on light. Aberration leads to blurring of the produced by an image-forming optical system. Makers of optical instruments need to correct optical systems to compensate for aberration, the articles on reflection, refraction and caustics discuss the general features of reflected and refracted rays. Aberrations fall into two classes, monochromatic and chromatic, monochromatic aberrations are caused by the geometry of the lens or mirror and occur both when light is reflected and when it is refracted. They appear even when using light, hence the name. Chromatic aberrations are caused by dispersion, the variation of a refractive index with wavelength. They do not appear when monochromatic light is used, if an otherwise perfect wavefront is aberrated by piston and tilt, it will still form a perfect, aberration-free image, only shifted to a different position. Defocus is the true optical aberration. The introduction of simple auxiliary terms, due to C. F. Gauss, named the focal lengths and focal planes, permits the determination of the image of any object for any system. The Gaussian theory, however, is true so long as the angles made by all rays with the optical axis are infinitely small. The investigations of James Clerk Maxwell and Ernst Abbe showed that the properties of these reproductions and these authors proved, however, that no optical system can justify these suppositions, since they are contradictory to the fundamental laws of reflection and refraction. Consequently, the Gaussian theory only supplies a convenient method of approximating to reality and this, and related general questions, have been treated — besides the above-mentioned authors — by M. Thiesen and H. Bruns by means of Sir W. R. Hamiltons characteristic function. Reference may also be made to the treatise of Czapski-Eppenstein, pp. 155–161, a review of the simplest cases of aberration will now be given. Let S be any system, rays proceeding from an axis point O under an angle u1 will unite in the axis point O1. The caustic, in the first case, resembles the sign >, if the angle u1 is very small, O1 is the Gaussian image, and O1 O2 is termed the longitudinal aberration, and O1R the lateral aberration of the pencils with aperture u2. This hole is termed the stop or diaphragm, Abbe used the term stop for both the hole and the limiting margin of the lens
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Projector
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A projector or image projector is an optical device that projects an image onto a surface, commonly a projection screen. Most projectors create an image by shining a light through a transparent lens. A virtual retinal display, or retinal projector, is a projector that projects an image directly on the retina instead of using a projection screen. The most common type of projector used today is called a video projector. Video projectors are digital replacements for earlier types of such as slide projectors. These earlier types of projectors were replaced with digital video projectors throughout the 1990s and early 2000s. The newest types of projectors are handheld projectors that use lasers or LEDs to project images and their projections are hard to see if there is too much ambient light. Movie theaters used a type of projector called a movie projector, spectators not always provided the details needed to differentiate between for instance a shadow play and a lantern projection. Many did not understand the nature of what they had seen, projections were often presented or perceived as magic or even as religious experiences, with most projectionists unwilling to share their secrets. Shadow play usually does not involve a projection device, but can be seen as a first step in the development of projectors. It evolved into more refined forms of puppetry in Asia. Projectors share a history with cameras in the camera obscura. The oldest known record of this principle is a description by Han Chinese philosopher Mozi, Mozi correctly asserted that the camera obscura image is inverted because light travels in straight lines from its source. In the 11th century Arab physicist Ibn al-Haytham described experiments with light through an opening in a darkened room. The use of a lens in the opening of a wall or closed window shutter of a room has been traced back to circa 1550. The shared history of camera and projector basically split with the introduction of the lantern in the later half of the 17th century. The camera obscura device would mostly live on as an aid in the form of tents. The oldest known objects that can project images are Chinese magic mirrors, the origins of these mirrors have been traced back to the Chinese Han dynasty and are also found in Japan. The mirrors were cast in bronze with a pattern embossed at the back, the pattern seen on the back of the mirror is seen in a projection when light is reflected from the polished front onto a wall or other surface
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Refracting telescope
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A refracting telescope is a type of optical telescope that uses a lens as its objective to form an image. The refracting telescope design was used in spy glasses and astronomical telescopes but is also used for long focus camera lenses. A refractors magnification is calculated by dividing the length of the objective lens by that of the eyepiece. Refractors were the earliest type of optical telescope, Galileo Galilei, happening to be in Venice in about the month of May 1609, heard of the invention and constructed a version of his own. Galileo then communicated the details of his invention to the public, all refracting telescopes use the same principles. The objective in a refracting telescope refracts or bends light and this refraction causes parallel light rays to converge at a focal point, while those not parallel converge upon a focal plane. The telescope converts a bundle of rays to make an angle α. The ratio β/α is called the angular magnification and it equals the ratio between the retinal image sizes obtained with and without the telescope. Refracting telescopes can come in different configurations to correct for image orientation. Because the image was formed by the bending of light, or refraction, the design Galileo Galilei used in 1609 is commonly called a Galilean telescope. It used a convergent objective lens and a divergent eyepiece lens, a Galilean telescope, because the design has no intermediary focus, results in a non-inverted and upright image. Galileo’s best telescope magnified objects about 30 times, because of flaws in its design, such as the shape of the lens and the narrow field of view, the images were blurry and distorted. Despite these flaws, the telescope was still enough for Galileo to explore the sky. The Galilean telescope could view the phases of Venus, and was able to see craters on the Moon, parallel rays of light from a distant object would be brought to a focus in the focal plane of the objective lens. The eyepiece lens intercepts these rays and renders them parallel once more, non-parallel rays of light from the object traveling at an angle α1 to the optical axis travel at a larger angle after they passed through the eyepiece. This leads to an increase in the apparent angular size and is responsible for the perceived magnification, the final image is a virtual image, located at infinity and is the same way up as the object. The Keplerian telescope, invented by Johannes Kepler in 1611, is an improvement on Galileos design and it uses a convex lens as the eyepiece instead of Galileos concave one. The advantage of this arrangement is that the rays of light emerging from the eyepiece are converging and this allows for a much wider field of view and greater eye relief, but the image for the viewer is inverted
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Primary mirror
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A primary mirror is the principal light-gathering surface of a reflecting telescope. The primary mirror of a telescope is a spherical or parabolic shaped disks of polished reflective metal, or in later telescopes. One of the first known reflecting telescopes, Newtons reflector of 1668, the next major change was to use silver on glass rather than metal, in the 19th century such was with the Crossley reflector. This was changed to vacuum deposited aluminum on glass, used on the 200-inch Hale telescope, solid primary mirrors have to sustain their own weight and not deform under gravity, which limits the maximum size for a single piece primary mirror. Segmented mirror configurations are used to get around the limitation on single primary mirrors. For example, the Giant Magellan Telescope will have seven 8.4 meter primary mirrors, with the resolving power equivalent to a 24.5 m optical aperture. The largest optical telescope in the world as of 2009 to use a non-segmented single-mirror as its mirror is the 8. S. /German/Italian Large Binocular Telescope has two 8.4 m mirrors. Both of these are smaller than the 10 m segmented primary mirrors on the two Keck telescope, the Hubble Space Telescope has a 2.4 m primary mirror. Radio and submillimeter telescopes use much larger dishes or antennae, which do not have to be made as precisely as the used in optical telescopes. The Arecibo Observatory uses a 305 m dish, which is the world largest single-dish radio telescope fixed to the ground, the Green Bank Telescope has the worlds largest steerable single radio dish with 100 m in diameter. There are largest radio arrays, composed of multiple dishes which have better image resolution, active optics Honeycomb mirror Liquid mirror List of largest optical reflecting telescopes List of telescope parts and construction Mirror mount Mirror support cell Secondary mirror
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Reflecting telescope
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A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the telescope which. Although reflecting telescopes produce other types of aberrations, it is a design that allows for very large diameter objectives. Almost all of the telescopes used in astronomy research are reflectors. Reflecting telescopes come in many variations and may employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use mirrors, the design is referred to as a catoptric telescope. The idea that curved mirrors behave like lenses dates back at least to Alhazens 11th century treatise on optics, the potential advantages of using parabolic mirrors, primarily reduction of spherical aberration with no chromatic aberration, led to many proposed designs for reflecting telescopes. The most notable being James Gregory, who published a design for a ‘reflecting’ telescope in 1663. It would be ten years, before the experimental scientist Robert Hooke was able to build this type of telescope, Isaac Newton has been generally credited with building the first reflecting telescope in 1668. It used a spherically ground metal primary mirror and a diagonal mirror in an optical configuration that has come to be known as the Newtonian telescope. A curved primary mirror is the reflector telescopes basic optical element that creates an image at the focal plane, the distance from the mirror to the focal plane is called the focal length. The primary mirror in most modern telescopes is composed of a glass cylinder whose front surface has been ground to a spherical or parabolic shape. A thin layer of aluminum is deposited onto the mirror. Some telescopes use primary mirrors which are made differently, molten glass is rotated to make its surface paraboloidal, and is kept rotating while it cools and solidifies. The resulting mirror shape approximates a desired paraboloid shape that requires grinding and polishing to reach the exact figure needed. Reflecting telescopes, just like any other system, do not produce perfect images. The use of mirrors avoids chromatic aberration but they produce other types of aberrations, to avoid this problem most reflecting telescopes use parabolic shaped mirrors, a shape that can focus all the light to a common focus. Field curvature - The best image plane is in general curved and it is sometimes corrected by a field flattening lens
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Catadioptric system
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A catadioptric optical system is one where refraction and reflection are combined in an optical system, usually via lenses and curved mirrors. Catadioptric combinations are used in focusing systems such as lights, headlamps, early lighthouse focusing systems, optical telescopes, microscopes. Other optical systems use lenses and mirrors are also referred to as catadioptric such as surveillance catadioptric sensors. Catadioptric combinations have been used in many optical systems. In the 1820s, Augustin-Jean Fresnel developed several catadioptric lighthouse reflectors, léon Foucault developed a catadioptric microscope in 1859 to counteract aberrations of using a lens to image objects at high power. In 1876 a French engineer, A. Mangin, invented what has come to be called the Mangin mirror, the two surfaces of the reflector have different radii to correct the aberration of the spherical mirror. Light passes through the glass twice, making the system act like a triplet lens. Mangin mirrors were used in searchlights, where they produced a true parallel beam. Catadioptric telescopes are optical telescopes that combine specifically shaped mirrors and lenses to form an image and their designs can have simple all-spherical surfaces and can take advantage of a folded optical path that reduces the mass of the telescope, making them easier to manufacture. Catadioptric dialytes are the earliest type of catadioptric telescope and they consist of a single-element refractor objective combined with a silver-backed negative lens. The first of these was the Hamiltonian telescope patented by W. F. Hamilton in 1814, there are several telescope designs that take advantage of placing one or more full-diameter lenses in front of a spherical primary mirror. Some of these designs have been adapted to create compact, long-focal-length catadioptric cassegrains, the Schmidt corrector, the first full-diameter corrector plate, was used in Bernhard Schmidts 1931 Schmidt camera. The relatively thin and lightweight corrector allows Schmidt cameras to be constructed in diameters up to 1.3 m, the design has lent itself to many Schmidt variants. Popular sub-types Schmidt–Cassegrain telescopes are one of the most popular commercial designs on the amateur astronomical market, the design replaces the Schmidt Camera film holder with a Cassegrain secondary mirror, making a folded optical path with a long focal length and a narrow field of view. Wartime secrecy kept these inventors from knowing about each others designs, albert Bouwers built a prototype meniscus telescope in August 1940 and patented it in February 1941. It used a spherically concentric meniscus and was suitable as a monochromatic astronomical camera. In a later design he added a cemented doublet to correct chromatic aberration, Dmitri Maksutov built a prototype for a similar type of meniscus telescope, the Maksutov telescope, in October 1941 and patented it in November of that same year. His design corrected spherical and chromatic aberrations by placing a weak negative-shaped meniscus corrector closer to the primary mirror, popular sub-types Maksutov–Cassegrain telescopes are the most commonly seen design that uses a meniscus corrector, a variant of the Maksutov telescope
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Angular resolution
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In scientific analysis, in general, the term resolution is used to describe the precision with which any instrument measures and records any variable in the specimen or sample under study. The imaging systems resolution can be limited either by aberration or by diffraction causing blurring of the image and these two phenomena have different origins and are unrelated. Aberrations can be explained by geometrical optics and can in principle be solved by increasing the optical quality —, on the other hand, diffraction comes from the wave nature of light and is determined by the finite aperture of the optical elements. The lens circular aperture is analogous to a version of the single-slit experiment. The interplay between diffraction and aberration can be characterised by the point spread function, the narrower the aperture of a lens the more likely the PSF is dominated by diffraction. If the distance is greater, the two points are well resolved and if it is smaller, they are regarded as not resolved, Rayleigh defended this criteria on sources of equal strength. Considering diffraction through an aperture, this translates into, θ =1.220 λ D where θ is the angular resolution, λ is the wavelength of light. The factor 1.220 is derived from a calculation of the position of the first dark circular ring surrounding the central Airy disc of the diffraction pattern and this number is more precisely 1.21966989. The first zero of the order-one Bessel function of the first kind J1 divided by π, the formal Rayleigh criterion is close to the empirical resolution limit found earlier by the English astronomer W. R. Dawes who tested human observers on close binary stars of equal brightness. The result, θ =4. 3% dip, modern image processing techniques including deconvolution of the point spread function allow resolution of binaries with even less angular separation. The angular resolution may be converted into a resolution, Δℓ. For a microscope, that distance is close to the length f of the objective. For this case, the Rayleigh criterion reads, Δ ℓ =1.220 f λ D. This is the size, in the plane, of smallest object that the lens can resolve. The size is proportional to wavelength, λ, and thus, for example and this result is related to the Fourier properties of a lens.220 f λ D =1.22 λ ⋅. Since this is the radius of the Airy disk, the resolution is better estimated by the diameter,2.44 λ ⋅ Point-like sources separated by a smaller than the angular resolution cannot be resolved. A single optical telescope may have a resolution less than one arcsecond. The angular resolution R of a telescope can usually be approximated by R = λ D where λ is the wavelength of the observed radiation, the Resulting R is in radians
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F-number
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The f-number of an optical system such as a camera lens is the ratio of the systems focal length to the diameter of the entrance pupil. It is a number that is a quantitative measure of lens speed. It is also known as the ratio, f-ratio, f-stop. The f-number is commonly indicated using a hooked f with the format f/N, the f-number N or f# is given by, N = f D where f is the focal length, and D is the diameter of the entrance pupil. It is customary to write f-numbers preceded by f/, which forms a mathematical expression of the pupil diameter in terms of f and N. Ignoring differences in light transmission efficiency, a lens with a greater f-number projects darker images, the brightness of the projected image relative to the brightness of the scene in the lenss field of view decreases with the square of the f-number. Doubling the f-number decreases the brightness by a factor of four. To maintain the same photographic exposure when doubling the f-number, the time would need to be four times as long. Most lenses have a diaphragm, which changes the size of the aperture stop. The entrance pupil diameter is not necessarily equal to the aperture stop diameter, a 100 mm focal length f/4 lens has an entrance pupil diameter of 25 mm. A200 mm focal length f/4 lens has a pupil diameter of 50 mm. The 200 mm lenss entrance pupil has four times the area of the 100 mm lenss entrance pupil, a T-stop is an f-number adjusted to account for light transmission efficiency. The word stop is sometimes confusing due to its multiple meanings, a stop can be a physical object, an opaque part of an optical system that blocks certain rays. In photography, stops are also a used to quantify ratios of light or exposure. The one-stop unit is known as the EV unit. On a camera, the setting is traditionally adjusted in discrete steps. Each stop is marked with its corresponding f-number, and represents a halving of the light intensity from the previous stop. This corresponds to a decrease of the pupil and aperture diameters by a factor of 1/2 or about 0.7071, each element in the sequence is one stop lower than the element to its left, and one stop higher than the element to its right
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Movie projector
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A movie projector is an opto-mechanical device for displaying motion picture film by projecting it onto a screen. Most of the optical and mechanical elements, except for the illumination, the first movie projector was the Zoopraxiscope, invented by British photographer Eadweard Muybridge in 1879. The zoopraxiscope projected images from rotating glass disks in rapid succession to give the impression of motion, the stop-motion images were initially painted onto the glass, as silhouettes. A second series of discs, made in 1892–94, used outline drawings printed onto the discs photographically, a more sophisticated movie projector was invented by Frenchman Louis Le Prince while working in Leeds. In 1888 Le Prince took out a patent for a 16-lens device that combined a motion picture camera with a projector, in 1888, he used an updated version of his camera to film the first ever motion picture, the Roundhay Garden Scene. The pictures were exhibited in Hunslet. The Lumière brothers invented the first successful movie projector and they made their first film, Sortie de lusine Lumière de Lyon, in 1894, which was publicly screened at LEden, La Ciotat a year later. The first commercial, public screening of cinematographic films happened in Paris on 28 December 1895, the cinematograph was also exhibited at the Paris Exhibition of 1900. At the Exhibition, films made by the Lumière Brothers were projected onto a screen measuring 16 by 21 meters. In 1999, digital projectors were being tried out in some movie theatres. These early projectors played the movie stored on a server and played back through the projector, due to their relatively low resolution, the images at the time showed pixelization blocks in some scenes, much like images on early widescreen televisions. By 2006, the advent of much higher 4K resolution digital projection had removed any traces of pixelization, the systems became more compact than the larger machines of four years earlier. By 2009, movie theatres started replacing the film projectors with digital projectors, in 2013, it was estimated that 92% of movie theatres in the United States had converted to digital, with 8% still playing film. In 2015, numerous popular filmmakers—including Quentin Tarantino and Christopher Nolan—lobbied large studios to commit to purchase an amount of 35 mm film from Kodak. The decision ensured that Kodaks 35mm film production would continue for several years, nowadays film projectors are considered obsolete as high-resolution digital projectors offer many advantages over traditional film units. For example, digital projectors contain no moving parts except fans, can be operated remotely and they also allow for much easier, less expensive, and more reliable storage and distribution of content, including the ability to display live broadcasts. According to the theory of the phi phenomenon, the brain constitutes an experience of apparent movement when presented with a sequence of near-identical still images. Persistence of vision should be compared with the phenomena of beta movement
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W. M. Keck Observatory
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The W. M. Keck Observatory is a two-telescope astronomical observatory at an elevation of 4,145 meters near the summit of Mauna Kea in the U. S. state of Hawaii. Both telescopes feature 10 m primary mirrors, currently among the largest astronomical telescopes in use, the combination of an excellent site, large optics and innovative instruments has created the two most scientifically productive telescopes on Earth. With a design in hand a search for the funding began, Keck of the W. M. Keck Foundation gave $70 million to fund the construction of the Keck I telescope. Construction of Keck I began in September 1985, with first light occurring on 24 November 1990 using only nine of the eventual 36 segments, with construction of the first telescope well advanced, further donations allowed the construction of a second telescope starting in 1991. The Keck I telescope began observations in May 1993, while first light for Keck II occurred on October 23,1996. The key advance that allowed the construction of the Keck Observatorys large telescopes was the ability to operate smaller mirror segments as a single, in the case of the Keck Observatory telescopes each of the primary mirrors is composed of 36 hexagonal segments that work together as a single unit. Each segment is 1.8 meters wide,7.5 centimeters thick, the mirrors were made from Zerodur glass-ceramic by the German company Schott AG. On the telescope, each segment is kept stable by a system of active optics, during observation, the computer-controlled system of sensors and actuators adjusts the position of each segment, relative to its neighbors, to an accuracy of four nanometers. This twice-per-second adjustment counters the effect of gravity as the telescope moves, each Keck Observatory telescope sits on an altazimuth mount. Most current 8–10 m class telescopes use altazimuth designs due to the structural requirements compared to older equatorial designs. This mounting style provides the greatest strength and stiffness for the least amount of steel, the total weight of each telescope is more than 300 tons. Two of the designs for the next generation 30 and 40 m telescopes use the same basic technology pioneered at Keck Observatory. Because of this difference in design, Keck Observatorys telescopes arguably remain the largest steerable. The telescopes are equipped with a suite of instruments, both cameras and spectrometers that allow observations across much of the visible and near infrared spectrum, construction of the telescopes was made possible through private grants totaling more than $140 million provided by the W. M. Keck Foundation. The National Aeronautics and Space Administration joined the partnership in October 1996, telescope time is allocated by the partner institutions. Caltech, the University of Hawaii System, and the University of California accept proposals from their own researchers, NASA accepts proposals from researchers based in the United States, while the National Optical Astronomy Observatory accept proposals from researchers around the world. MOSFIRE MOSFIRE is a third generation instrument for the W. M. Keck Observatory, MOSFIRE was delivered to Keck Observatory on February 8,2012 and first light on the Keck I telescope was obtained on April 4,2012. Bars move in each side to form up to 46 short slits
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International Standard Book Number
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The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
