A stereoscope is a device for viewing a stereoscopic pair of separate images, depicting left-eye and right-eye views of the same scene, as a single three-dimensional image.

A typical stereoscope provides each eye with a lens that makes the image seen through it appear larger and more distant and usually also shifts its apparent horizontal position, so that for a person with normal binocular depth perception the edges of the two images seemingly fuse into one "stereo window". In current practice, the images are prepared so that the scene appears to be beyond this virtual window, through which objects are sometimes allowed to protrude, but this was not always the custom. A divider or other view-limiting feature is usually provided to prevent each eye from being distracted by also seeing the image intended for the other eye.

Most people can, with practice and some effort, view stereoscopic image pairs in 3D without the aid of a stereoscope, but the physiological depth cues resulting from the unnatural combination of eye convergence and focus required will be unlike those experienced when actually viewing the scene in reality, making an accurate simulation of the natural viewing experience impossible and tending to cause eye strain and fatigue.

Although more recent devices such as realist-format 3D slide viewers and the View-Master are also stereoscopes, the word is now most commonly associated with viewers designed for the standard-format stereo cards that enjoyed several waves of popularity from the 1850s to the 1930s as a home entertainment medium.

Devices such as polarized, anaglyph and shutter glasses which are used to view two actually superimposed or intermingled images, rather than two physically separate images, are not categorized as stereoscopes.

History
Wheatstone stereoscope
The earliest type of stereoscope was invented by Sir Charles Wheatstone in 1838. It used a pair of mirrors at 45 degree angles to the user's eyes, each reflecting a picture located off to the side. It demonstrated the importance of binocular depth perception by showing that when two pictures simulating left-eye and right-eye views of the same object are presented so that each eye sees only the image designed for it, but apparently in the same location, the brain will fuse the two and accept them as a view of one solid three-dimensional object. Wheatstone's stereoscope was introduced in the year before the first practical photographic process became available, so drawings were used. This type of stereoscope has the advantage that the two pictures can be very large if desired.

Brewster stereoscope
Contrary to a common assertion, David Brewster did not invent the stereoscope, as he himself was often at pains to make clear. A rival of Wheatstone, Brewster credited the invention of the device to a Mr. Elliot, a "Teacher of Mathematics" from Edinburgh, who, according to Brewster, conceived of the idea as early as 1823 and, in 1839, constructed "a simple stereoscope without lenses or mirrors", consisting of a wooden box 18 inches long, 7 inches wide and 4 inches high, which was used to view drawn landscape transparencies, since photography had yet to be invented. Brewster's personal contribution was the suggestion to use lenses for uniting the dissimilar pictures in 1849; and accordingly the lenticular stereoscope (lens based) may fairly be said to be his invention. This allowed a reduction in size, creating hand-held devices, which became known as Brewster Stereoscopes, much admired by Queen Victoria when they were demonstrated at the Great Exhibition of 1851.

Holmes stereoscope
A Holmes stereoscope, the most popular form of 19th century stereoscope
In 1861 Oliver Wendell Holmes created and deliberately did not patent a handheld, streamlined, much more economical viewer than had been available before. The stereoscope, which dates from the 1850s, consisted of two prismatic lenses and a wooden stand to hold the stereo card. This type of stereoscope remained in production for a century and there are still companies making them in limited production currently. It is primarily American, although it is often named "Mexican stereoscope."

Modern use
In the mid-20th century the View-Master stereoscope (patented 1939), with its rotating cardboard disks containing image pairs, was popular first for 'virtual tourism' and then as a toy. In 2010, Hasbro started producing a stereoscope designed to hold an iPhone or iPod Touch, called the My3D. Apps on the mobile phone substitute for stereo cards. The underlying technology is otherwise unchanged from earlier stereoscopes.

Several fine arts photographers and graphic artists have and continue to produce original artwork to be viewed using stereoscopes.

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Open season is a hunting term used to describe the time of the year when a particular wildlife species is allowed to be hunted as per local wildlife conservation law. It is timed to occur when the population is at its maximum and to avoid periods of vulnerability, it avoids the peak breeding period when members of a species are particularly vulnerable and avoids any disruption to mating, which may affect productivity.

By extension, the period that is not the "Open season" is known as the "Closed season".

A hunting season is the time when it is legal to hunt and kill a particular species.

In the United States, each state has primary responsibility and authority over the hunting of wildlife that resides within state boundaries. State wildlife agencies that sell hunting licenses are the best source of information regarding hunting seasons, areas open/closed to hunting, etc. (Hunting of migratory birds such as ducks and geese is managed cooperatively by state fish and wildlife agencies and the U.S. Fish and Wildlife Service). Migratory waterfowl hunters must possess both a state hunting license and a Federal Migratory Bird Hunting and Conservation Stamp (Duck Stamp), and each hunter needs a Harvest Information Program (HIP) number for each state in which they hunt migratory birds.

Hunting seasons often come during the time of year when the temperature is often below that which a particular breed is required to maintain a normal body temperature.
 
Hunting is the practice of pursuing any living thing, but usually wildlife for food, recreation, or trade. In present-day use, the term refers to lawful hunting, as distinguished from poaching, which is the killing, trapping or capture of the hunted species contrary to applicable law. The species which are hunted are referred to as game, and are usually mammals and migratory or non-migratory gamebirds.

Hunting can also involve the elimination of vermin, as a means of pest control to prevent diseases caused by overpopulation. Hunting advocates state that hunting can be a necessary component of modern wildlife management, for example to help maintain a population of healthy animals within an environment's ecological carrying capacity when natural checks such as predators are absent. In the United States, wildlife managers are frequently part of hunting regulatory and licensing bodies, where they help to set rules on the number, manner and conditions in which game may be hunted.

The pursuit, capture and release, or capture for food of fish is called fishing, which is not commonly categorised as a form of hunting. Trapping is also usually considered a separate activity. It is also not considered hunting to pursue animals without intent to kill them, as in wildlife photography or birdwatching. The practice of hunting for plants or mushrooms is a colloquial term for foraging or gathering.

Skilful tracking and acquisition of an elusive target has caused the word hunting to be used in the vernacular as a metaphor, as in "bargain hunting" or "hunting down corruption and waste".

United States
North American hunting pre-dates the United States by thousands of years, and was an important part of many pre-Columbian Native American cultures. Native Americans retain some hunting rights, and are exempt from some laws as part of Indian treaties and otherwise under federal law—examples include eagle feather laws and exemptions in the Marine Mammal Protection Act. This is considered particularly important in Alaskan native communities.

Regulation of hunting is primarily regulated by state law; additional regulations are imposed through United States environmental law in the case of migratory birds and endangered species. Regulations vary widely from state to state, and govern the areas, time periods, techniques and methods by which specific game animals may be hunted. Some states make a distinction between protected species and unprotected species (often vermin or varmints for which there are no hunting regulations). Hunters of protected species require a hunting license in all states, for which completion of a hunting safety course is sometimes a prerequisite.

Typically game animals are divided into several categories for regulatory purposes. Typical categories, along with example species, are as follows:

Big game: white-tailed deer, mule deer, moose, elk, caribou, bighorn sheep, pronghorn, boar, javelina
Small game: rabbit, hare, squirrel, oppossum, raccoon, porcupine, skunk, ring-tailed cat, armadillo
Furbearers: beaver, red fox, mink, pine martin, musk rat, otter, bobcat
Predators: cougar (mountain lion and panther), bear, coyote
Upland game bird: grouse, turkey, chukar, pheasant, quail, dove
Waterfowl: duck, teal, merganser, geese, swan
Hunting big game typically requires a "tag" for each animal harvested. Tags must be purchased in addition to the hunting license, and the number of tags issued to an individual is typically limited. In cases where there are more prospective hunters than the quota for that species, tags are usually assigned by lottery. Tags may be further restricted to a specific area or wildlife management unit. Hunting migratory waterfowl requires a duck stamp from the Fish and Wildlife Service.

Harvest of animals other than big game is typically restricted by a bag limit and a possession limit. A bag limit is a maximum number of a specific animal species that an individual can harvest in a single day. A possession limit is a maximum number of a specific animal species that can be in an individual's possession at any time.

Shooting
Gun usage in hunting is typically regulated by game category, area within the state, and time period. Regulations for big game hunting often specify a minimum calibre or muzzle energy for firearms. The use of rifles is often banned for safety reasons in areas with high population densities or limited topographic relief. Regulations may also limit or ban the use of lead in ammunition because of environmental concerns. Specific seasons for bow hunting or muzzle-loading black powder guns are often established to limit competition with hunters using more effective weapons.

Hunting in the United States is not associated with any particular class or culture; a 2006 poll showed eventy-eight percent of Americans supported legal hunting, although relatively few Americans actually hunt. At the beginning of the 21st century, just six percent of Americans hunted. Southerners in states along the eastern seaboard hunted at a rate of five percent, slightly below the national average, and while hunting was more common in other parts of the South at nine percent, these rates did not surpass those of the Plains states, where twelve percent of Midwesterners hunted. Hunting in other areas of the country fell below the national average. Overall, in the 1996–2006 period, the number of hunters over the age of sixteen declined by ten percent, a drop attributable to a number of factors including habitat loss and changes in recreation habits.

Regulation of hunting within the United States dates from the 19th century. Some modern hunters see themselves as conservationists and sportsmen in the mode of Theodore Roosevelt and the Boone and Crockett Club. Local hunting clubs and national organisations provide hunter education and help protect the future of the sport by buying land for future hunting use. Some groups represent a specific hunting interest, such as Ducks Unlimited, Pheasants Forever, or Delta Waterfowl Foundation. Many hunting groups also participate in lobbying the federal government and state government.

Each year, nearly $200 million in hunters' federal excise taxes are distributed to state agencies to support wildlife management programs, the purchase of lands open to hunters, and hunter education and safety classes. Since 1934 the sale of Federal Duck Stamps, a required purchase for migratory waterfowl hunters over sixteen-years-old, has raised over $700 million to help purchase more than 5,200,000 acres (8,120 sq mi; 21,000 km2) of habitat for the National Wildlife Refuge System lands that support waterfowl and many other wildlife species, and are often open to hunting. States also collect monies from hunting licenses to assist with management of game animals, as designated by law. A key task of federal and state park rangers and game wardens is to enforce laws and regulations related to hunting, including species protection, hunting seasons, and hunting bans.

Varmint hunting is an American phrase for the selective killing of non-game animals seen as pests. While not always an efficient form of pest control, varmint hunting achieves selective control of pests while providing recreation, and is much less regulated. Varmint species are often responsible for detrimental effects on crops, livestock, landscaping, infrastructure, and pets. Some animals, such as wild rabbits or squirrels, may be utilised for fur or meat, but often no use is made of the carcass. Which species are "varmints" depends on the circumstance and area. Common varmints may include various rodents, coyotes, crows, foxes, feral cats, and feral hogs. Some animals once considered varmints are now protected, such as wolves. In the US state of Louisiana, a non-native rodent known as a nutria have become so destructive to the local ecosystem that the state has initiated a bounty program to help control the population. Feral dogs and cats, rats, starlings, English sparrows, and pigeons may be hunted without a hunting license in the United States.

Fair chase
The principles of the fair chase have been a part of the American hunting tradition for over one-hundred years. The role of the hunter-conservationist, popularised by Theodore Roosevelt, has been central to the development of the modern fair chase tradition.

When internet hunting was introduced in 2005, allowing people to hunt over the internet using remotely controlled guns, the practice was widely criticised by hunters as violating the principles of fair chase. As a representative of the National Rifle Association (NRA) explained, "[t]he NRA has always maintained that fair chase, being in the field with your firearm or bow, is an important element of hunting tradition. Sitting at your desk in front of your computer, clicking at a mouse, has nothing to do with hunting".

Ranches
Indian blackbuck, nilgai, axis deer, fallow deer and barasingha can now be found on hunting ranches in Texas, where they were introduced for sport hunting. Hunters can pay upwards of $4000 as fees for hunting a barasingha.