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Lens Speed
Lens speed is the maximum aperture diameter, or minimum f-number, of a photographic lens. A lens with a larger than average maximum aperture (that is, a smaller minimum f-number) is called a "fast lens" because it can achieve the same exposure as an average lens with a faster shutter speed. Conversely, a smaller maximum aperture (larger minimum f-number) is "slow" because it delivers less light intensity and requires a slower (longer) shutter speed. A fast lens speed is desirable in taking pictures in dim light, for stability with long telephoto lenses, and for controlling depth of field and bokeh, especially in portrait photography, as well as for sports photography and photojournalism. Lenses may also be referred to as being "faster" or "slower" than one another; so an 3.5 lens can be described as faster than an 5.6 despite 3.5 not generally being considered "fast" outright. What ''is'' considered fast largely depends on focal length, image diameter (i.e. format covered, such a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spherical Aberration
In optics, spherical aberration (SA) is a type of aberration found in optical systems that have elements with spherical surfaces. This phenomenon commonly affects lenses and curved mirrors, as these components are often shaped in a spherical manner for ease of manufacturing. Light rays that strike a spherical surface off-centre are refracted or reflected more or less than those that strike close to the centre. This deviation reduces the quality of images produced by optical systems. The effect of spherical aberration was first identified in the 11th century by Ibn al-Haytham who discussed it in his work Kitāb al-Manāẓir. Overview A spherical lens has an aplanatic point (i.e., no spherical aberration) only at a lateral distance from the optical axis that equals the radius of the spherical surface divided by the index of refraction of the lens material. Spherical aberration makes the focus of telescopes and other instruments less than ideal. This is an important effect, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
APS-C
Advanced Photo System type-C (APS-C) is an image sensor format approximately equivalent in size to the Advanced Photo System film negative in its C ("Classic") format, of 25.1×16.7 mm, an aspect ratio of 3:2 and Ø 30.15 mm field diameter. It is therefore also equivalent in size to the Super 35 motion picture film format, which has the dimensions of 24.89 mm × 18.66 mm (0.980 in × 0.735 in) and Ø 31.11 mm field diameter. Sensors approximating these dimensions are used in many digital single-lens reflex cameras (DSLRs), mirrorless interchangeable-lens cameras (MILCs), and a few large-sensor live-preview digital cameras. APS-C size sensors are also used in a few digital rangefinder camera, rangefinders. Such sensors exist in many different variants depending on the manufacturer and camera model. All APS-C variants are considerably smaller than 35 mm standard film which measures 36×24 mm. Because of this, devices with APS-C sensors a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Canon EF 85mm Lens
The EF 85mm lenses are a group of medium Telephoto lens, telephoto prime lens, prime photographic lens, lenses made by Canon Inc. that share the same focal length. These lenses have an Canon EF lens mount, EF type mount that fits the Canon Canon EOS, EOS line of cameras. This 85mm focal length is "perfect for portraiture" as labeled by Canon and practicing professionals, due to the focal length creating just the right perspective for both the subject and the background. The 85mm is most commonly used for head and shoulder type portraiture, upper torso portraiture and selective floral photography. It will commonly be found in the kits of photographers that shoot wedding, birthdays, and other events involving people. These photographers would also carry a Canon EF 70-200mm lens, 70-200mm for complementing the longer focal lengths and when extremely shallow depth of field is not needed. EF 85mm 1.2L USM The EF 85mm 1.2L USM is a professional Canon L lens, L series lens. Canon marke ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Canon EF 50mm Lens
The EF 50mm lenses are a group of normal lens, normal prime lens, prime photographic lens, lenses made by Canon (company), Canon that share the same focal length. These lenses are based on the classic double-Gauss lens, with the f/1.8 being a standard six-element double-Gauss with an air gap and powers between element 2 and 3 and its Lens speed, faster cousins adding additional elements. The 50mm focal length, when used with a 35mm film or full-frame sensor, has been widely considered to match the perspective seen by the human eye. Canon 50mm lenses have an Canon EF lens mount, EF type mount that fits the Canon EOS line of cameras. When pairing a 50mm lens to a Canon DSLR with an APS-C sized sensor, the crop factor effectively turns the 50mm focal length into an 80mm field of view. Seven EF 50mm lenses have been sold by Canon: * 1.0L USM (discontinued, replaced by 1.2L USM) * 1.2L USM * 1.4 USM * 1.8 (discontinued, replaced by 1.8 II) * 1.8 II (discontinued, replaced by 1.8 STM ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linear Approximation
In mathematics, a linear approximation is an approximation of a general function (mathematics), function using a linear function (more precisely, an affine function). They are widely used in the method of finite differences to produce first order methods for solving or approximating solutions to equations. Definition Given a twice continuously differentiable function f of one real number, real variable, Taylor's theorem for the case n = 1 states that f(x) = f(a) + f'(a)(x - a) + R_2 where R_2 is the remainder term. The linear approximation is obtained by dropping the remainder: f(x) \approx f(a) + f'(a)(x - a). This is a good approximation when x is close enough to since a curve, when closely observed, will begin to resemble a straight line. Therefore, the expression on the right-hand side is just the equation for the tangent line to the graph of f at (a,f(a)). For this reason, this process is also called the tangent line approximation. Linear approximations in this case are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Square Root Of 2
The square root of 2 (approximately 1.4142) is the positive real number that, when multiplied by itself or squared, equals the number 2. It may be written as \sqrt or 2^. It is an algebraic number, and therefore not a transcendental number. Technically, it should be called the ''principal'' square root of 2, to distinguish it from the negative number with the same property. Geometrically, the square root of 2 is the length of a diagonal across a Unit square, square with sides of one unit of length; this follows from the Pythagorean theorem. It was probably the first number known to be irrational number, irrational. The fraction (≈ 1.4142857) is sometimes used as a good Diophantine approximation, rational approximation with a reasonably small denominator. Sequence in the On-Line Encyclopedia of Integer Sequences consists of the digits in the decimal expansion of the square root of 2, here truncated to 60 decimal places: : History The Babylonian clay tablet YBC 7289 (–1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Canon 85mm Comparison (front)
Canon or Canons may refer to: Arts and entertainment * Canon (fiction), the material accepted as officially written by an author or an ascribed author * Literary canon, an accepted body of works considered as high culture ** Western canon, the body of high culture literature, music, philosophy, and works of art that is highly valued in the West * Canon of proportions, a formally codified set of criteria deemed mandatory for a particular artistic style of figurative art * Canon (music), a type of composition * Canon (hymnography), a type of hymn used in Eastern Orthodox Christianity. * ''Canon'' (album), a 2007 album by Ani DiFranco * ''Canon'' (film), a 1964 Canadian animated short * ''Canon'' (manga), by Nikki * Canonical plays of William Shakespeare * ''The Canon'' (Natalie Angier book), a 2007 science book by Natalie Angier * ''The Canon'' (podcast), concerning film Brands and enterprises * Canon Inc., a Japanese imaging and optical products corporation * Château ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
1911 Encyclopædia Britannica
Events January * January 1 – A decade after federation, the Northern Territory and the Australian Capital Territory are added to the Commonwealth of Australia. * January 3 ** 1911 Kebin earthquake: An earthquake of 7.7 Moment magnitude scale, moment magnitude strikes near Almaty in Russian Turkestan, killing 450 or more people. ** Siege of Sidney Street in London: Two Latvian people, Latvian anarchists die, after a seven-hour siege against a combined police and military force. Home Secretary Winston Churchill arrives to oversee events. * January 4 – Comparison of the Amundsen and Scott expeditions, Amundsen and Scott expeditions: Robert Falcon Scott's British Terra Nova Expedition, ''Terra Nova'' Expedition to the South Pole arrives in the Antarctic and establishes a base camp at Cape Evans on Ross Island. * January 5 – Egypt's Zamalek SC is founded as a general sports and Association football club by Belgian lawyer George Merzbach as Q ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Coating
An optical coating is one or more thin-film optics, thin layers of material deposited on an optical component such as a lens (optics), lens, prism (optics), prism or mirror, which alters the way in which the optic reflection (physics), reflects and transmittance, transmits light. These coatings have become a key technology in the field of optics. One type of optical coating is an anti-reflective coating, which reduces unwanted reflections from surfaces, and is commonly used on glasses, spectacle and camera lenses. Another type is the high-reflector coating, which can be used to produce mirrors that reflect greater than 99.99% of the light that falls on them. More complex optical coatings exhibit high reflection over some range of wavelengths, and anti-reflection over another range, allowing the production of dichroism, dichroic dichroic filter, thin-film filters. Types of coating The simplest optical coatings are thin layers of metals, such as aluminium, which are deposited on g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Manufacturing
Optical manufacturing and testing is the process of manufacturing and testing optical components. It spans a wide range of manufacturing procedures and optical test configurations. The manufacture of a conventional spherical lens typically begins with the generation of the optic's rough shape by grinding a glass blank. This can be done, for example, with ring tools. Next, the lens surface is polished to its final form. Typically this is done by lapping—rotating and rubbing the rough lens surface against a tool with the desired surface shape, with a mixture of abrasives and fluid in between. Typically a carved pitch tool is used to polish the surface of a lens. The mixture of abrasive is called slurry and it is typically made from cerium or zirconium oxide in water with lubricants added to facilitate pitch tool movement without sticking to the lens. The particle size in the slurry is adjusted to get the desired shape and finish. Types of lapping include planetary lapping, d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lens Design
Optical lens design is the process of designing a lens to meet a set of performance requirements and constraints, including cost and manufacturing limitations. Parameters include surface profile types (spherical, aspheric, holographic, diffractive, etc.), as well as radius of curvature, distance to the next surface, material type and optionally tilt and decenter. The process is computationally intensive, using ray tracing or other techniques to model how the lens affects light that passes through it. Design requirements Performance requirements can include: #Optical performance (image quality): This is quantified by various metrics, including encircled energy, modulation transfer function, Strehl ratio, ghost reflection control, and pupil performance (size, location and aberration control); the choice of the image quality metric is application specific. #Physical requirements such as weight, static volume, dynamic volume, center of gravity and overall configuration requirements. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
