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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 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.
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.
A Fresnel lens is a type of composite compact lens originally developed by French physicist Augustin-Jean Fresnel (1788–1827) for lighthouses. It has been called "the invention that saved a million ships."
The Very Large Telescope (VLT) is a telescope facility operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2 m across, which are generally used separately but can be used together to achieve very high angular resolution. The four separate optical telescopes are known as Antu, Kueyen, Melipal, and Yepun, which are all words for astronomical objects in the Mapuche language. The telescopes form an array which is complemented by four movable Auxiliary Telescopes (ATs) of 1.8 m aperture.
Subaru Telescope is the 8.2-meter (320 in) flagship telescope of the National Astronomical Observatory of Japan, located at the Mauna Kea Observatory on Hawaii. It is named after the open star cluster known in English as the Pleiades. It had the largest monolithic primary mirror in the world from its commissioning until 2005.
Angular resolution describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object, thereby making it a major determinant of image resolution. It is used in optics applied to light waves, in antenna theory applied to radio waves, and in acoustics applied to sound waves. The closely related term spatial resolution refers to the precision of a measurement with respect to space, which is directly connected to angular resolution in imaging instruments. The Rayleigh criterion shows that the minimum angular spread that can be resolved by an image forming system is limited by diffraction to the ratio of the wavelength of the waves to the aperture width. For this reason, high resolution imaging systems such as astronomical telescopes, long distance telephoto camera lenses and radio telescopes have large apertures.
An optical telescope is a telescope that gathers and focuses light, mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct view, or to make a photograph, or to collect data through electronic image sensors.
In optics, the Airy disk and Airy pattern are descriptions of the best-focused spot of light that a perfect lens with a circular aperture can make, limited by the diffraction of light. The Airy disk is of importance in physics, optics, and astronomy.
A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved. Most coronagraphs are intended to view the corona of the Sun, but a new class of conceptually similar instruments are being used to find extrasolar planets and circumstellar disks around nearby stars as well as host galaxies in quasars and other similar objects with active galactic nuclei (AGN).
A zone plate is a device used to focus light or other things exhibiting wave character. Unlike lenses or curved mirrors, zone plates use diffraction instead of refraction or reflection. Based on analysis by French physicist Augustin-Jean Fresnel, they are sometimes called Fresnel zone plates in his honor. The zone plate's focusing ability is an extension of the Arago spot phenomenon caused by diffraction from an opaque disc.
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, 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 worsen as the aperture diameter increases, while the Airy circle is smallest for large apertures.
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. 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.
Antoine Émile Henry Labeyrie is a French astronomer, who held the Observational astrophysics chair at the Collège de France between 1991 and 2014, where he is currently professor emeritus. He is working with the Hypertelescope Lise association, which aims to develop an extremely large astronomical interferometer with spherical geometry that might theoretically show features on Earth-like worlds around other suns, as its president. He is a member of the French Academy of Sciences in the Sciences of the Universe section. Between 1995 and 1999 he was director of the Haute-Provence Observatory.
Apodization is an optical filtering technique. Its literal translation is "removing the foot". It is the technical term for changing the shape of a mathematical function, an electrical signal, an optical transmission or a mechanical structure. In optics, it is primarily used to remove Airy disks caused by diffraction around an intensity peak, improving the focus.
A telescope is an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. The first known practical telescopes were refracting telescopes invented in the Netherlands at the beginning of the 17th century, by using glass lenses. They were used for both terrestrial applications and astronomy.
A microlens is a small lens, generally with a diameter less than a millimetre (mm) and often as small as 10 micrometres (µm). The small sizes of the lenses means that a simple design can give good optical quality but sometimes unwanted effects arise due to optical diffraction at the small features. A typical microlens may be a single element with one plane surface and one spherical convex surface to refract the light. Because micro-lenses are so small, the substrate that supports them is usually thicker than the lens and this has to be taken into account in the design. More sophisticated lenses may use aspherical surfaces and others may use several layers of optical material to achieve their design performance.
Advanced Telescope for High-ENergy Astrophysics (ATHENA) is an X-ray observatory mission selected by ESA within its Cosmic Vision Program to address the Hot and Energetic Universe scientific theme. Athena will operate in the energy range of 0.2–12keV and will offer spectroscopic and imaging capabilities exceeding those of currently operating X-ray astronomy satellites – e.g. the Chandra X-ray Observatory and XMM-Newton – by at least one order of magnitude on several parameter spaces simultaneously.
The International X-ray Observatory (IXO) is a cancelled X-ray telescope that was to be launched in 2021 as a joint effort by NASA, the European Space Agency (ESA), and the Japan Aerospace Exploration Agency (JAXA). In May 2008, ESA and NASA established a coordination group involving all three agencies, with the intent of exploring a joint mission merging the ongoing XEUS and Constellation-X projects. This proposed the start of a joint study for IXO. NASA was forced to cancel the observatory due to budget constrains in fiscal year 2012. ESA however decided to reboot the mission on its own developing Advanced Telescope for High Energy Astrophysics as a part of Cosmic Vision program.
The Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL), is a space telescope planned for launch in 2029 as the fourth medium-class mission of the European Space Agency's Cosmic Vision programme. The mission is aimed at observing at least 1,000 known exoplanets using the transit method, studying and characterising the planets' chemical composition and thermal structures. Compared to James Webb Space Telescope, ARIEL will have more observing time available for planet characterisation but a much smaller telescope.
Nautilus Deep Space Observatory (NDSO) is a proposed deep space fleet of space telescopes designed to search for biosignatures of life in the atmospheres of exoplanets.
References
- 1 2 L. Koechlin; D. Serre; P. Duchon (2005). "High resolution imaging with Fresnel interferometric arrays:suitability for exoplanet detection" (PDF). Astronomy and Astrophysics. 443 (2): 12 Chapter 9, Paragraph 1. Bibcode:2005A&A...443..709K. doi:10.1051/0004-6361:20052880 . Retrieved 8 September 2009.
- ↑ L. Koechlin; D. Serre; P. Duchon (2005). "High resolution imaging with Fresnel interferometric arrays:suitability for exoplanet detection" (PDF). Astronomy and Astrophysics. 443 (2): 1 Chapter 1, Paragraph 2. Bibcode:2005A&A...443..709K. doi:10.1051/0004-6361:20052880 . Retrieved 8 September 2009.
The focal length of such a Fresnel array can vary from 200 m to 20 km, depending on the array type and wavelength used.
- 1 2 3 4 Shiga, David (1 May 2008). "Telescope could focus light without a mirror or lens". New Scientist.
- 1 2 Laurent Koechlin. "The UV side of galaxy evolution with FRESNEL imagers" (PDF). Laboratoire d’Astrophysique de Toulouse-Tarbes. Université de Toulouse. Retrieved 8 September 2009.
- ↑ Koechlin, L; Serre, D; Deba, P (2009). "The Fresnel interferometric imager". Astrophysics and Space Science. 320 (1–3): 225. Bibcode:2009Ap&SS.320..225K. doi:10.1007/s10509-008-9793-8. hdl: 10871/16076 . S2CID 119749945.
- 1 2 3 Laurent Koechlin; Denis Serre; Paul Deba; Truswin Raksasataya; Christelle Peillon. "The Fresnel Interferometric Imager, Proposal to ESA Cosmic Vision 2007" (PDF). pp. 2–3. Retrieved 9 September 2009.
- 1 2 3 "Proposed Telescope Focuses Light Without Mirror Or Lens". science.slashdot.org.
- ↑ "Twinkle, twinkle, little planet: An undervalued optical trick may help to find life in other solar systems". The Economist. June 9, 2012.
