|
Diffraction Spike
Diffraction spikes are lines radiating from bright light sources, causing what is known as the starburst effect or sunstars in photographs and in vision. They are artifacts caused by light diffracting around the support vanes of the secondary mirror in reflecting telescopes, or edges of non-circular camera apertures, and around eyelashes and eyelids in the eye. While similar in appearance, this is a different effect to "vertical smear" or "blooming" that appears when bright light sources are captured by a charge-coupled device (CCD) image sensor. Causes Support vanes In the vast majority of reflecting telescope designs, the secondary mirror has to be positioned at the central axis of the telescope and so has to be held by struts within the telescope tube. No matter how fine these support rods are they diffract the incoming light from a subject star and this appears as diffraction spikes which are the Fourier transform of the support struts. The spikes represent a loss of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diaphragm (optics)
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. Iris diaphragms versus other types A natural optical system that has a diaphra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anastigmat
An anastigmat or anastigmatic lens is a photographic lens completely corrected for the three main optical aberrations: spherical aberration, coma (optics), coma, and Astigmatism (optical systems), astigmatism. Early lenses often included the word ''Anastigmat'' in their name to advertise this new feature (''Doppel-Anastigmat'', ''Voigtländer Anastigmat Skopar'', etc.). History Early designs The first ''Anastigmat'' was designed by Paul Rudolph (physicist), Paul Rudolph for the German firm Carl Zeiss AG in 1890 and marketed as the ''Protar''; it consisted of four elements in two groups, as an asymmetric arrangement of two cemented achromatic lens doublets and was improved to a five-element, two-group design in 1891, substituting a cemented triplet for the rear group. In 1892, the Swiss mathematician Emil von Höegh designed the ''Dagor'' (aka ''Double Anastigmatic Goerz'') for Goerz (company), Goerz, a symmetric lens with six elements in two groups, made of two cemented triple ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffraction Spikes Due To Non-circular Aperture
Diffraction is the deviation of waves from straight-line propagation without any change in their energy due to an obstacle or through an aperture. The diffracting object or aperture effectively becomes a secondary source of the propagating wave. Diffraction is the same physical effect as interference, but interference is typically applied to superposition of a few waves and the term diffraction is used when many waves are superposed. Italian scientist Francesco Maria Grimaldi coined the word ''diffraction'' and was the first to record accurate observations of the phenomenon in 1660. In classical physics, the diffraction phenomenon is described by the Huygens–Fresnel principle that treats each point in a propagating wavefront as a collection of individual spherical wavelets. The characteristic pattern is most pronounced when a wave from a coherent source (such as a laser) encounters a slit/aperture that is comparable in size to its wavelength, as shown in the inserted image. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NGC 7469
NGC 7469 is an intermediate spiral galaxy in the constellation of Pegasus (constellation), Pegasus. NGC 7469 is located about 200 million light-years away from Earth, which means, given its apparent dimensions, that NGC 7469 is approximately 142,000 light-years across. It was discovered by William Herschel on November 12, 1784. NGC 7469 is a type I Seyfert galaxy, characterised by its bright nucleus. It is also a Luminous infrared galaxy, luminous infrared source with a powerful Starburst region, starburst embedded into its circumnuclear region. The coexistence of a circumnuclear starburst ring and an active galactic nucleus have turned NGC 7469 into a key target for studying their relation. NGC 7469 interacts with its smaller companion IC 5283, forming a pair collectively known in the ''Atlas of Peculiar Galaxies'' as Arp 298. NGC 7469 is one of the first galaxies observed by the James Webb Space Telescope. Characteristics Active galactic nucleus NGC 7469 is a type 1.2 Seyfe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Westerlund 1
Westerlund 1 (abbreviated Wd1, sometimes called Ara Cluster) is a compact young super star cluster about 3.8 kiloparsec, kpc (12,000 ly) away from Earth. It is thought to be the most massive young star cluster in the Milky Way, and was discovered by Bengt Westerlund in 1961 but remained largely unstudied for many years due to high interstellar extinction, interstellar absorption in its direction. In the future, it will probably evolve into a globular cluster. The cluster contains a large number of rare, evolved, high-mass stars, including: 6 yellow hypergiants, 4 red supergiants including Westerlund 1-26, one of the List of largest known stars, largest known stars, 24 Wolf-Rayet stars, a luminous blue variable, many OB star, OB supergiants, and an unusual supergiant B(e) star, sgB[e] star which has been proposed to be the remnant of a recent Stellar collision, stellar merger. In addition, X-ray observations have revealed the presence of the anomalous X-ray pulsar CXOU J164710.2- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
James Webb Space Telescope
The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. As the largest telescope in space, it is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, List of the most distant astronomical objects, distant, or faint for the Hubble Space Telescope. This enables investigations across many fields of astronomy and cosmology, such as observation of the Population III star, first stars and the Galaxy formation and evolution, formation of the first galaxies, and detailed atmospheric characterization of potentially habitable exoplanets. Although the Webb's mirror diameter is 2.7 times larger than that of the Hubble Space Telescope, it produces images of comparable optical resolution, resolution because it observes in the longer-wavelength infrared spectrum. The longer the wavelength of the spectrum, the larger the information-gathering surface required (mirrors in the infrared spectrum or antenna a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Segmented Mirror
A segmented mirror is an array of smaller mirrors designed to act as segments of a single large curved mirror. The segments can be either spherical or asymmetric (if they are part of a larger parabolic reflector). They are used as objectives for large reflecting telescopes. To function, all the mirror segments have to be polished to a precise shape and actively aligned by a computer-controlled active optics system using actuators built into the mirror support cell. The concept was pioneered by Guido Horn D'Arturo, who built the first working segmented mirror in 1952, after twenty years of research; It was later independently rediscovered and further developed under the leadership of Dr. Jerry Nelson at the Lawrence Berkeley National Laboratory and University of California during the 1980s, and since then all the necessary technologies have spread worldwide to the point that essentially all future large optical telescopes plan to use segmented mirrors. Application Ther ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telescope
A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects – an optical telescope. Nowadays, the word "telescope" is defined as a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors. The first known practical telescopes were refracting telescopes with glass lenses and were invented in the Netherlands at the beginning of the 17th century. They were used for both terrestrial applications and astronomy. The reflecting telescope, which uses mirrors to collect and focus light, was invented within a few decades of the first refracting telescope. In the 20th century, many new types of telescopes were invented, including radio telescopes in t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
B&H Photo
B&H Photo Video (also known as B&H Photo and B&H and B&H Foto & Electronics Corporation) is an American photo and video equipment retailer founded in 1973, based in Manhattan, New York City. B&H conducts business primarily through online e-commerce consumer sales and business to business sales, as they only have one retail location. While initially a photo and film shop, B&H has grown into one of the largest electronic retailers in the U.S., selling over 400,000 products. Their warehouse is located in Florence, New Jersey. History B&H opened in 1973 as a storefront film shop at 17 Warren Street in Tribeca, and took its name from the initials of owners Blimie Schreiber and her husband, Herman. Later in the 1970s, B&H moved to 119 West 17th Street between Sixth and Seventh Avenues in the Photo District and began to expand its stock to a wider range of film and photography products. In the 1990s, the company began selling various electronics, including computers, lighting, and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
F-number
An f-number is a measure of the light-gathering ability of an optical system such as a camera lens. It is calculated by dividing the system's focal length by the diameter of the entrance pupil ("clear aperture").Smith, Warren ''Modern Optical Engineering'', 4th Ed., 2007 McGraw-Hill Professional, p. 183. The f-number is also known as the focal ratio, f-ratio, or f-stop, and it is key in determining the depth of field, diffraction, and Exposure (photography), exposure of a photograph. The f-number is dimensionless number, dimensionless and is usually expressed using a lower-case Ƒ, hooked f with the format ''N'', where ''N'' is the f-number. The f-number is also known as the inverse relative aperture, because it is the Multiplicative inverse, inverse of the relative aperture, defined as the aperture diameter divided by focal length. The relative aperture indicates how much light can pass through the lens at a given focal length. A lower f-number means a larger relative apertur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
