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Aperture
In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image of the aperture and focal length of an optical system determine the cone angle of a bundle of rays that comes to a focus in the image plane. An optical system typically has many structures that limit ray bundles (ray bundles are also known as ''pencils'' of light). These structures may be the edge of a lens or mirror, or a ring or other fixture that holds an optical element in place or may be a special element such as a diaphragm placed in the optical path to limit the light admitted by the system. In general, these structures are called stops, and the aperture stop is the stop that primarily determines the cone of rays that an optical system accepts (see entrance pupil). As a result, it also determines the ray cone angle and brightne ... [...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 of a photograph. The f-number is dimensionless and is usually expressed using a lower-case 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 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 aperture and more light entering the system, while a higher f-number means a s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aberration In Optical Systems
In optics, aberration is a property of optical systems, such as Lens (optics), lenses and mirrors, that causes the ''image'' created by the optical system to not be a faithful reproduction of the ''object'' being observed. Aberrations cause the image formed by a lens to be blurred, distorted in shape or have color fringing or other effects not seen in the object, 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 i ... [...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] |
Depth Of Field
The depth of field (DOF) is the distance between the nearest and the farthest objects that are in acceptably sharp focus (optics), focus in an image captured with a camera. See also the closely related depth of focus. Factors affecting depth of field For cameras that can only focus on one object distance at a time, depth of field is the distance between the nearest and the farthest objects that are in acceptably sharp focus in the image. "Acceptably sharp focus" is defined using a property called the "circle of confusion". The depth of field can be determined by focal length, distance to subject (object to be imaged), the acceptable circle of confusion size, and aperture. Limitations of depth of field can sometimes be overcome with various techniques and equipment. The approximate depth of field can be given by: \text \approx \frac for a given maximum acceptable circle of confusion , focal length , f-number , and distance to subject . As distance or the size of the acc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Entrance Pupil
In an optical system, the entrance pupil is the optical image of the physical aperture stop, as 'seen' through the optical elements in front of the stop. The corresponding image of the aperture stop as seen through the optical elements behind it is called the ''exit pupil''. The entrance pupil defines the cone of rays that can enter and pass through the optical system. Rays that fall outside of the entrance pupil will not pass through the system. If there is no lens in front of the aperture (as in a pinhole camera), the entrance pupil's location and size are identical to those of the aperture. Optical elements in front of the aperture will produce a magnified or diminished image of the aperture that is displaced from the aperture location. The entrance pupil is usually a virtual image: it lies behind the first optical surface of the system. The entrance pupil is a useful concept for determining the size of the cone of rays that an optical system will accept. Once the size ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telecentric Lens
A telecentric lens is a special optical lens (often an objective lens or a camera lens) that has its entrance or exit pupil, or both, at infinity. The size of images produced by a telecentric lens is insensitive to either the distance between an object being imaged and the lens, or the distance between the image plane and the lens, or both, and such an optical property is called ''telecentricity''. Telecentric lenses are used for precision optical two-dimensional measurements, reproduction (e.g., photolithography), and other applications that are sensitive to the image magnification or the angle of incidence of light. The simplest way to make a lens telecentric is to put the aperture stop at one of the lens's focal points. This allows only rays including the chief rays (light rays that pass through the center of the aperture stop), that will be about parallel to the optical axis on the other side of the lens, to pass the optical system for any object point in the field of view. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exit Pupil
In optics, the exit pupil is a virtual aperture in an optical system. Only ray (optics), rays which pass through this virtual aperture can exit the system. The exit pupil is the image of the aperture stop in the optics that follow it. In a optical telescope, telescope or compound microscope, this image is the image of the Objective (optics), objective element(s) as produced by the eyepiece. The size and shape of this disc is crucial to the instrument's performance, because the observer's eye can see light only if it passes through the aperture. The term ''exit pupil'' is also sometimes used to refer to the diameter of the virtual aperture. Older literature on optics sometimes refers to the exit pupil as the ''Ramsden disc'', named after English instrument-maker Jesse Ramsden. Visual instruments To use an optical instrument, the entrance pupil of the viewer's eye (the image of the pupil, anatomical pupil as seen through the cornea) must be aligned with and be of similar size to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Objective Lens
In optical engineering, an objective is an optical element that gathers light from an object being observed and focuses the light rays from it to produce a real image of the object. Objectives can be a single lens or mirror, or combinations of several optical elements. They are used in microscopes, binoculars, telescopes, cameras, slide projectors, CD players and many other optical instruments. Objectives are also called object lenses, object glasses, or objective glasses. Microscope objectives The objective lens of a microscope is the one at the bottom near the sample. At its simplest, it is a very high-powered magnifying glass, with very short focal length. This is brought very close to the specimen being examined so that the light from the specimen comes to a focus inside the microscope tube. The objective itself is usually a cylinder containing one or more lenses that are typically made of glass; its function is to collect light from the sample. Magnification One of the ... [...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 optical instruments, instruments that use or Photodetector, detect it. Optics usually describes the behaviour of visible light, visible, ultraviolet, and infrared light. Light is a type of electromagnetic radiation, and 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 electromagnetism, classical electromagnetic description of light, however complete electromagnetic descriptions of light are 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 Ray (optics), rays that travel in straight lines and bend when they pass through or reflect from surfaces. Physical optics is a more comprehensive mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical System
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. Light is a type of electromagnetic radiation, and 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, however complete electromagnetic descriptions of light are 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 cann ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ray (optics)
In optics, a ray is an idealized geometrical model of light or other electromagnetic radiation, obtained by choosing a curve that is perpendicular to the ''wavefronts'' of the actual light, and that points in the direction of energy flow. Rays are used to model the propagation of light through an optical system, by dividing the real light field up into discrete rays that can be computationally propagated through the system by the techniques of '' ray tracing''. This allows even very complex optical systems to be analyzed mathematically or simulated by computer. Ray tracing uses approximate solutions to Maxwell's equations that are valid as long as the light waves propagate through and around objects whose dimensions are much greater than the light's wavelength. '' Ray optics'' or ''geometrical optics'' does not describe phenomena such as diffraction, which require wave optics theory. Some wave phenomena such as interference can be modeled in limited circumstances by adding ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photometry (astronomy)
In astronomy, photometry, from Greek '' photo-'' ("light") and '' -metry'' ("measure"), is a technique used in astronomy that is concerned with measuring the flux or intensity of light radiated by astronomical objects. This light is measured through a telescope using a photometer, often made using electronic devices such as a CCD photometer or a photoelectric photometer that converts light into an electric current by the photoelectric effect. When calibrated against standard stars (or other light sources) of known intensity and colour, photometers can measure the brightness or apparent magnitude of celestial objects. The methods used to perform photometry depend on the wavelength region under study. At its most basic, photometry is conducted by gathering light and passing it through specialized photometric optical bandpass filters, and then capturing and recording the light energy with a photosensitive instrument. Standard sets of passbands (called a photometric system) are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
