Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes when viewing distant objects. Most binoculars are sized to be held using both hands, although sizes vary widely from opera glasses to large pedestal-mounted military models.
Birdwatching, or birding, is the observing of birds, either as a recreational activity or as a form of citizen science. A birdwatcher may observe by using their naked eye, by using a visual enhancement device like binoculars or a telescope, by listening for bird sounds, watching public webcams, or by viewing smart bird feeder cameras.
In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an animal has eyes on opposite sides of its head and shares no field of view between them, like in some animals.
A spotting scope is a compact lightweight portable telescope optimized for detailed observation of distant objects. They are used as tripod mounted optical enhancement devices for various outdoor activities such as birdwatching, skygazing and other naturalist activities, for hunting and target shooting to verify a marksman's shot placements, for tactical ranging and surveillance, and for any other application that requires higher magnification than ordinary binoculars.
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 to produce binocular vision, which allows stereopsis and depth perception.
Depth perception is the ability to perceive distance to objects in the world using the visual system and visual perception. It is a major factor in perceiving the world in three dimensions. Depth perception happens primarily due to stereopsis and accommodation of the eye.
Horace Gundry Alexander was an English Quaker teacher, writer, pacifist and ornithologist. He was the youngest of four sons of Joseph Gundry Alexander (1848–1918), two other sons being the ornithologists Wilfred Backhouse Alexander and Christopher James Alexander (1887–1917). He was a friend of Mahatma Gandhi.
Sálim Moizuddin Abdul Ali was an Indian ornithologist and naturalist. Sometimes referred to as the "Birdman of India", Salim Ali was the first Indian to conduct systematic bird surveys across India and wrote several bird books that popularized ornithology in India. He became a key figure behind the Bombay Natural History Society after 1947 and used his personal influence to garner government support for the organisation, create the Bharatpur bird sanctuary and prevent the destruction of what is now the Silent Valley National Park.
Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often voluntary. However, when occurring involuntarily, it results from impaired function of the extraocular muscles, where both eyes are still functional, but they cannot turn to target the desired object. Problems with these muscles may be due to mechanical problems, disorders of the neuromuscular junction, disorders of the cranial nerves that innervate the muscles, and occasionally disorders involving the supranuclear oculomotor pathways or ingestion of toxins.
A monopod, also called a unipod, is a single staff or pole used to help support cameras, binoculars, rifles or other precision instruments in the field.
Digiscoping is a neologism for afocal photography, using a (digital) camera to record distant images through the eyepiece of an optical telescope.
Duane syndrome is a congenital rare type of strabismus most commonly characterized by the inability of the eye to move outward. The syndrome was first described by ophthalmologists Jakob Stilling (1887) and Siegmund Türk (1896), and subsequently named after Alexander Duane, who discussed the disorder in more detail in 1905.
The term Jacob's staff is used to refer to several things, also known as cross-staff, a ballastella, a fore-staff, a ballestilla, or a balestilha. In its most basic form, a Jacob's staff is a stick or pole with length markings; most staffs are much more complicated than that, and usually contain a number of measurement and stabilization features. The two most frequent uses are:
An Abbe–Koenig prism is a type of reflecting prism, used to invert an image. They are commonly used in binoculars and some telescopes for this purpose. The prism is named after Ernst Abbe and Albert Koenig.
The Moon is the largest natural satellite of and the closest major astronomical object to Earth. The Moon may be observed by using a variety of optical instruments, ranging from the naked eye to large telescopes. The Moon is the only celestial body upon which surface features can be discerned with the unaided eyes of most people.
Vision is the most important sense for birds, since good eyesight is essential for safe flight. Birds have a number of adaptations which give visual acuity superior to that of other vertebrate groups; a pigeon has been described as "two eyes with wings". Birds are theropod dinosaurs, and the avian eye resembles that of other sauropsids, with ciliary muscles that can change the shape of the lens rapidly and to a greater extent than in the mammals. Birds have the largest eyes relative to their size in the animal kingdom, and movement is consequently limited within the eye's bony socket. In addition to the two eyelids usually found in vertebrates, bird's eyes are protected by a third transparent movable membrane. The eye's internal anatomy is similar to that of other vertebrates, but has a structure, the pecten oculi, unique to birds.
Bioptics, also known as a bioptic in the singular, and sometimes more formally termed a bioptic telescope, is a term for a pair of vision-enhancement lenses. They magnify between two and six times, and are used to improve distance vision for those with severely impaired eyesight, especially those with albinism. They can either be a combination of head-mounted eyeglasses and binoculars, or be designed to attach to existing glasses. Some use monoculars which have small telescopes mounted on, in, or behind their regular lenses, so that they can look through either the regular lens or the telescope. Newer designs use smaller lightweight mini telescopes magnifying up to six times, which can be embedded into the spectacle glass and improve aesthetic appearance. The mini telescopic eyeglasses have been shown to be used in the treatment of nystagmus. In some jurisdictions, those with low vision may be permitted to drive automobiles when using Bioptics.
The eagle eye is among the sharpest in the animal kingdom, with an eyesight estimated at 4 to 8 times stronger than that of the average human. Although an eagle may only weigh 10 pounds (4.5 kg), its eyes are roughly the same size as those of a human. Eagle weight varies: a small eagle could weigh 700 grams (1.5 lb), while a larger one could weigh 6.5 kilograms (14 lb); an eagle of about 10 kilograms (22 lb) weight could have eyes as big as that of a human who weighs 200 pounds (91 kg). Although the size of the eagle eye is about the same as that of a human being, the back side shape of the eagle eye is flatter. Their eyes are stated to be larger in size than their brain, by weight. Color vision with resolution and clarity are the most prominent features of eagles' eyes, hence sharp-sighted people are sometimes referred to as "eagle-eyed". Eagles can identify five distinctly colored squirrels and locate their prey even if hidden.
Signilskär is one of the westernmost islands in Finland, being part of the archipelago of Åland in the Gulf of Bothnia. The island, along with Katajaluoto, Hamnskär, and North and South Västerskär, makes up part of the municipality of Hammarland. Beyond Signilskär is Märket, the westernmost point of Finland.
An Uppendahl prism is an erecting prism, i.e. a special reflection prism that is used to invert an image. The erecting system consists of three partial prisms made of optical glass with a high refractive index cemented together to form a symmetric assembly and is used in microscopy as well as in binoculars technology.
