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Crystal Ball
A crystal ball, also known as an orbuculum or crystal sphere, is a crystal or glass ball and common fortune-telling object. It is generally associated with the performance of clairvoyance and scrying in particular. In more recent times, the crystal ball has been used for creative photography with the term lensball commonly used to describe a crystal ball used as a photography prop. History In the first century CE, Pliny the Elder describes use of crystal balls by soothsayers (''"crystallum orbis"'', later written in Medieval Latin by scribes as ''orbuculum''). By the fifth century CE, scrying was widespread within the Roman Empire and was condemned by the early medieval Christian Church as heretical. Dr. John Dee was a noted British mathematician, astronomer, astrologer, geographer, and consultant to Queen Elizabeth I. He devoted much of his life to alchemy, divination, and Hermetic philosophy, of which the use of crystal balls was often included. Crystal gazing was a popu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John William Waterhouse - The Crystal Ball
John is a common English name and surname: * John (given name) * John (surname) John may also refer to: New Testament Works * Gospel of John, a title often shortened to John * First Epistle of John, often shortened to 1 John * Second Epistle of John, often shortened to 2 John * Third Epistle of John, often shortened to 3 John People * John the Baptist (died c. AD 30), regarded as a prophet and the forerunner of Jesus Christ * John the Apostle (lived c. AD 30), one of the twelve apostles of Jesus * John the Evangelist, assigned author of the Fourth Gospel, once identified with the Apostle * John of Patmos, also known as John the Divine or John the Revelator, the author of the Book of Revelation, once identified with the Apostle * John the Presbyter, a figure either identified with or distinguished from the Apostle, the Evangelist and John of Patmos Other people with the given name Religious figures * John, father of Andrew the Apostle and Saint Peter * Pope John ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Romani People
The Romani (also spelled Romany or Rromani , ), colloquially known as the Roma, are an Indo-Aryan ethnic group, traditionally nomadic itinerants. They live in Europe and Anatolia, and have diaspora populations located worldwide, with significant concentrations in the Americas. In the English language, the Romani people are widely known by the exonym Gypsies (or Gipsies), which is considered pejorative by many Romani people due to its connotations of illegality and irregularity as well as its historical use as a racial slur. For versions (some of which are cognates) of the word in many other languages (e.g., , , it, zingaro, , and ) this perception is either very small or non-existent. At the first World Romani Congress in 1971, its attendees unanimously voted to reject the use of all exonyms for the Romani people, including ''Gypsy'', due to their aforementioned negative and stereotypical connotations. Linguistic and genetic evidence suggests that the Roma originated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Aberrations
In optics, aberration is a property of optical systems, such as lenses, that causes light to be spread out over some region of space rather than focused to a point. Aberrations cause the image formed by a lens to be blurred or distorted, with the nature of the distortion depending on the type of aberration. Aberration can be defined as 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 (or does not diverge from) a single point after transmission through the system. Aberrations occur because the simple paraxial theory is not a completely accurate model of the effect of an optical system on light, rather than due to flaws in the optical elements. An image-forming optical system with aberration will produce an image which is not sharp. Makers of optical instruments need to correct optical systems to compensate for aberration. Aberration can be anal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Field Curvature
Petzval field curvature, named for Joseph Petzval, describes the optical aberration in which a flat object normal to the optical axis (or a non-flat object past the hyperfocal distance) cannot be brought properly into focus on a flat image plane. Field curvature can be corrected with the use of a field flattener, designs can also incorporate a curved focal plane like in the case of the human eye in order to improve image quality at the focal surface. It is not to be confused with flat-field correction, which refers to brightness uniformity. Analysis Consider an "ideal" single-element lens system for which all planar wave fronts are focused to a point at distance ''f'' from the lens. Placing this lens the distance ''f'' from a flat image sensor, image points near the optical axis will be in perfect focus, but rays off axis will come into focus before the image sensor, dropping off by the cosine of the angle they make with the optical axis. This is less of a problem when the im ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coma (optics)
In optics (especially telescopes), the coma (), or comatic aberration, in an optical system refers to aberration inherent to certain optical designs or due to imperfection in the lens or other components that results in off-axis point sources such as stars appearing distorted, appearing to have a tail (coma) like a comet. Specifically, coma is defined as a variation in magnification over the entrance pupil. In refractive or diffractive optical systems, especially those imaging a wide spectral range, coma can be a function of wavelength, in which case it is a form of chromatic aberration. Overview Coma is an inherent property of telescopes using parabolic mirrors. Unlike a spherical mirror, a bundle of parallel rays parallel to the optical axis will be perfectly focused to a point (the mirror is free of spherical aberration), no matter where they strike the mirror. However, this is only true if the rays are parallel to the axis of the parabola. When the incoming rays strike the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Focus (optics)
In geometrical optics, a focus, also called an image point, is a 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, called the blur circle. 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, which is caused by diffraction from the optical system's aperture. Aberrations tend to worsen 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, and out of focus if light is not well converged. The border between these is sometimes defined using a "circle of confusion" criterion. A principal focus or focal point is a special focus: * For a lens, or a spherical or parabolic mirror, it is a point ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Refractive Index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or refracted, when entering a material. This is described by Snell's law of refraction, , where ''θ''1 and ''θ''2 are the angle of incidence and angle of refraction, respectively, of a ray crossing the interface between two media with refractive indices ''n''1 and ''n''2. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the critical angle for total internal reflection, their intensity ( Fresnel's equations) and Brewster's angle. The refractive index can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is , and similarly the wavelength in that medium is , where ''Π... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optics
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties. Most optical phenomena can be accounted for by using the classical electromagnetic description of light. Complete electromagnetic descriptions of light are, however, often difficult to apply in practice. Practical optics is usually done using simplified models. The most common of these, geometric optics, treats light as a collection of rays that travel in straight lines and bend when they pass through or reflect from surfaces. Physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radius Of Curvature
In differential geometry, the radius of curvature, , is the reciprocal of the curvature. For a curve, it equals the radius of the circular arc which best approximates the curve at that point. For surfaces, the radius of curvature is the radius of a circle that best fits a normal section or combinations thereof. Definition In the case of a space curve, the radius of curvature is the length of the curvature vector. In the case of a plane curve, then is the absolute value of : R \equiv \left, \frac \ = \frac, where is the arc length from a fixed point on the curve, is the tangential angle and is the curvature. Formula In 2D If the curve is given in Cartesian coordinates as , i.e., as the graph of a function, then the radius of curvature is (assuming the curve is differentiable up to order 2): : R =\left, \frac \, \qquad\mbox\quad y' = \frac,\quad y'' = \frac, and denotes the absolute value of . If the curve is given parametrically by functions and , then the radius o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spherical Lens
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), usually arranged along a common axis. Lenses are made from materials such as glass or plastic, and are ground and polished or molded to a desired shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. 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. Lenses are used in various imaging devices like telescopes, binoculars and cameras. They are also used as visual aids in glasses to correct defects of vision such as myopia and hypermetropia. History The word '' lens'' comes from '' lēns'', the Latin name of the lentil (a seed of a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alexander (magician)
Claude Alexander Conlin (June 30, 1880 – August 5, 1954), also known as Alexander, C. Alexander, Alexander the Crystal Seer, and Alexander the Man Who Knows, was an American spiritual author, vaudeville magician who specialized in mentalism and psychic reading acts, dressed in Oriental style robes and a feathered turban, and often used a crystal ball as a prop. In addition to performing, he also worked privately for clients, giving readings. He was the author of several pitch books, New Thought pamphlets, and psychology books, as well as texts for stage performers. His stage name was "Alexander," and as an author he wrote under the name "C. Alexander." Life and stage career Alexander was born on June 30, 1880 in Alexandria, South Dakota, the son of Berthold Michael James Conlin and Martha Michaels. Within the family Claude Alexander was known as "C. A." and his brother Clarence Berthold Conlin was known as "C. B." Clarence B. had a successful career as an attorney and he also ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magic (illusion)
Magic, which encompasses the subgenres of illusion, stage magic, and close up magic, among others, is a performing art in which audiences are entertained by tricks, effects, or illusions of seemingly impossible feats, using natural means. It is to be distinguished from paranormal magic which are effects claimed to be created through supernatural means. It is one of the oldest performing arts in the world. Modern entertainment magic, as pioneered by 19th-century magician Jean-Eugène Robert-Houdin, has become a popular theatrical art form. In the late 19th and early 20th centuries, magicians such as Maskelyne and Devant, Howard Thurston, Harry Kellar, and Harry Houdini achieved widespread commercial success during what has become known as "the Golden Age of Magic." During this period, performance magic became a staple of Broadway theatre, vaudeville, and music halls. Magic retained its popularity in the television age, with magicians such as Paul Daniels, David Copperfield ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
