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Baden-Powell's Unilens
The unilens monocular is a simple refracting telescope for field use, designed by Robert Baden-Powell, 1st Baron Baden-Powell, Robert Baden-Powell. Consisting of only one Lens (optics), lens, it is the simplest of all telescopes, and while occupying very little space can still magnify a distant image up to about four times. The nature of its operation however does not accommodate to everyone's visual acuity, with only three out of four people able to use it. Description and use The unilens monocular is simply a 2.5 inch (6.4 cm) diameter convex lens with a 6 foot (1.8 m) focal length, equivalent to +0.55 dioptres. In use the eye is closer than 6 feet to the lens (usually 3–4 feet) and thus between the lens and its principal focus. Accommodation (eye), Eye accommodation required is similar to that when viewing objects in the far distance, but more so as actual accommodation is made for somewhere beyond accommodation for infinity. Because of this unusual requi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selfie Stick
A selfie stick is used to take photographs or video by positioning a digital camera device, typically a smartphone, beyond the normal range of the arm. This allows for shots to be taken at angles and distances that would not have been possible with the human arm by itself. The sticks are typically extensible, with a handle on one end and an adjustable clamp on the other end to hold the device in place. As their name suggests, they are most commonly used for taking selfies with camera phones. Some are connected to a smartphone via its jack plug, while others are tethered using Bluetooth controls. The connection between the device and the selfie stick lets the user decide when to take the picture or start recording a video by clicking a button located on the handle. Models designed for compact cameras have a mirror behind the viewscreen so that the shot can be lined up. In contrast to a monopod for stabilising a camera on the ground, a selfie stick's arm is thickest and strongest at ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monocular
A monocular is a compact refracting telescope used to magnify images of distant objects, typically using an optical prism to ensure an erect image, instead of using relay lenses like most telescopic sights. The volume and weight of a monocular are typically less than half of a pair of binoculars with similar optical properties, making it more portable and also less expensive. This is because binoculars are essentially a pair of monoculars packed together — one for each eye. As a result, monoculars only produce two-dimensional images, while binoculars can use two parallaxed images (each for one eye) to produce binocular vision, which allows stereopsis and depth perception. Monoculars are ideally suited to those application where three-dimensional perception is not needed, or where compactness and low weight are important (e.g. hiking). Monoculars are also sometimes preferred where difficulties occur using both eyes through binoculars due to significant eyesight variation ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Autostereoscopy
Autostereoscopy is any method of displaying stereoscopic images (adding binocular perception of 3D depth) without the use of special headgear, glasses, something that affects vision, or anything for eyes on the part of the viewer. Because headgear is not required, it is also called "glasses-free 3D" or "glassesless 3D". There are two broad approaches currently used to accommodate motion parallax and wider viewing angles: eye-tracking, and multiple views so that the display does not need to sense where the viewer's eyes are located. Examples of autostereoscopic displays technology include lenticular lens, parallax barrier, and may include Integral imaging, but notably do not include volumetric display or holographic displays. Technology Many organizations have developed autostereoscopic 3D displays, ranging from experimental displays in university departments to commercial products, and using a range of different technologies. The method of creating autostereoscopic flat panel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reflecting Telescope
A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternative to the refracting telescope which, at that time, was a design that suffered from severe chromatic aberration. Although reflecting telescopes produce other types of optical aberrations, it is a design that allows for very large diameter objectives. Almost all of the major telescopes used in astronomy research are reflectors. Many variant forms are in use and some employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use mirrors, the design is sometimes referred to as a catoptrics, catoptric telescope. From the time of Newton to the 1800s, the mirror itself was made of metal usually speculum metal. This type included Newton's first designs and eve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Umbrella
An umbrella or parasol is a folding canopy supported by wooden or metal ribs that is usually mounted on a wooden, metal, or plastic pole. It is designed to protect a person against rain or sunlight. The term ''umbrella'' is traditionally used when protecting oneself from rain, with ''parasol'' used when protecting oneself from sunlight, though the terms continue to be used interchangeably. Often the difference is the material used for the canopy; some parasols are not waterproof, and some umbrellas are transparent. Umbrella canopies may be made of fabric or flexible plastic. There are also combinations of parasol and umbrella that are called ''en-tout-cas'' (French for "in any case"). Umbrellas and parasols are primarily hand-held portable devices sized for personal use. The largest hand-portable umbrellas are golf umbrellas. Umbrellas can be divided into two categories: fully collapsible umbrellas, in which the metal pole supporting the canopy retracts, making the umbrella sm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trekking Pole
Trekking poles (also known as hiking poles, hiking sticks or walking poles) are a common hiking accessory that function to assist walkers with their rhythm, to provide stability, and reduce strain on joints on rough terrain. Description When in use, modern trekking poles resemble ski poles as they have many features in common, such as baskets at the bottom to prevent the pole sinking through unstable surfaces, and rubber-padded handles and wrist straps to strengthen holding grip. Their maximum length is usually 135 cm (54 inches), however, unlike ski poles, they are often made in two or three sections and can be extended and retracted as necessary for use and collapsed for storage or transport. When fully retracted it may be possible to attach them to a backpack. Some poles come with spring (device), spring-loaded sections to aid walking under normal conditions and to reduce wrist strain, but such devices may only add unwanted weight and noise to the poles. They are usually made f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Walking Stick
A walking stick or walking cane is a device used primarily to aid walking, provide postural stability or support, or assist in maintaining a good posture. Some designs also serve as a fashion accessory, or are used for self-defense. Walking sticks come in many shapes and sizes and some have become collector's items. People with disabilities may use some kinds of walking sticks as a crutch but a walking cane is not designed for full weight support and is instead designed to help with balance. The walking stick has also historically been known to be used as a self defensive weapon and may conceal a knife or sword – as in a swordstick or swordcane. Hikers use walking sticks, also known as trekking poles, pilgrim's staffs, hiking poles, or hiking sticks, for a wide variety of purposes: as a support when going uphill or as a brake when going downhill; as a balance point when crossing streams, swamps, or other rough terrain; to feel for obstacles in the path; to test mud and wat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Accommodation (eye)
Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies. In this, distances vary for individuals from the far point—the maximum distance from the eye for which a clear image of an object can be seen, to the near point—the minimum distance for a clear image. Accommodation usually acts like a reflex, including part of the accommodation-vergence reflex, but it can also be consciously controlled. Mammals, birds and reptiles vary their eyes' optical power by changing the form of the elastic lens using the ciliary body (in humans up to 15 dioptres in the mean). Fish and amphibians vary the power by changing the distance between a rigid lens and the retina with muscles. The young human eye can change focus from distance (infinity) to as near as 6.5 cm from the eye. This dramatic change in focal power of the eye of approximately 15 dioptres (the reciprocal of focal length in metres) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Refracting Telescope
A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens (optics), lens as its objective (optics), objective to form an image (also referred to a dioptrics, dioptric telescope). The refracting telescope design was originally used in spyglasses and astronomy, astronomical telescopes but is also used for long-focus lens, long-focus camera lenses. Although large refracting telescopes were very popular in the second half of the 19th century, for most research purposes, the refracting telescope has been superseded by the reflecting telescope, which allows larger apertures. A refractor's magnification is calculated by dividing the focal length of the objective lens by that of the eyepiece. Refracting telescopes typically have a lens at the front, then a optical train, long tube, then an eyepiece or instrumentation at the rear, where the telescope view comes to focus. Originally, telescopes had an objective of one element, but a century later, tw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Principal Focus
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] |
Dioptre
A dioptre (British spelling) or diopter (American spelling) is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, 1 dioptre = 1 m−1. It is normally used to express the optical power of a lens or curved mirror, which is a physical quantity equal to the reciprocal of the focal length, expressed in metres. For example, a 3-dioptre lens brings parallel rays of light to focus at metre. A flat window has an optical power of zero dioptres, as it does not cause light to converge or diverge. Dioptres are also sometimes used for other reciprocals of distance, particularly radii of curvature and the vergence of optical beams. The main benefit of using optical power rather than focal length is that the thin lens formula has the object distance, image distance, and focal length all as reciprocals. Additionally, when relatively thin lenses are placed close together their powers approximately add. Thus, a thin 2.0-dioptre lens placed close to a t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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