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.
The earliest stereoscopes, "both with reflecting mirrors and with refracting prisms", were invented by Sir Charles Wheatstone and constructed for him by optician R. Murray in 1832.Herbert Mayo shortly described Wheatstone's discovery in his book Outlines of Human Physiology (1833) and claimed that Wheatstone was about to publish an essay about it. It was only one of many projects of Wheatstone's and he first presented his findings on 21 June 1838 to the Royal College of London. In this presentation he 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 processes became available, so initially drawings were used. The mirror type of stereoscope has the advantage that the two pictures can be very large if desired.
Contrary to a common assertion, David Brewster did not invent the stereoscope, as he himself was often at pains to make clear. 18 inches (46 cm) long, 7 inches (18 cm) wide and 4 inches (10 cm) high, which was used to view drawn landscape transparencies, since photography had yet to become widespread. 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.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
Brewster was unable to find in Britain an instrument maker capable of working with his design, so he took it to France, where the stereoscope was improved by Jules Duboscq who made stereoscopes and stereoscopic daguerreotypes, and a famous picture of Queen Victoria that was displayed at The Great Exhibition.Almost overnight a 3D industry developed and 250,000 stereoscopes were produced and a great number of stereoviews, stereo cards, stereo pairs or stereographs were sold in a short time. Stereographers were sent throughout the world to capture views for the new medium and feed the demand for 3D images. Cards were printed with these views often with explanatory text when the cards were looked at through the double-lensed viewer, sometimes also called a stereopticon , a common misnomer.
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.
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. In 2014, Google released the template for a papercraft stereoscope called Google Cardboard. Apps on the mobile phone substitute for stereo cards; these apps can also sense rotation and expand the stereoscope's capacity into that of a full-fledged virtual reality device. 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.
A simple stereoscope is limited in the size of the image that may be used. A more complex stereoscope uses a pair of horizontal periscope-like devices, allowing the use of larger images that can present more detailed information in a wider field of view. The stereoscope is essentially an instrument in which two photographs of the same object, taken from slightly different angles, are simultaneously presented, one to each eye. This recreates the way which in natural vision, each eye is seeing the object from a slightly different angle, since they are separated by several inches, which is what gives humans natural depth perception. Each picture is focused by a separate lens, and by showing each eye a photograph taken several inches apart from each other and focused on the same point, it recreates the natural effect of seeing things in three dimensions.
A moving image extension of the stereoscope has a large vertically mounted drum containing a wheel upon which are mounted a series of stereographic cards which form a moving picture. The cards are restrained by a gate and when sufficient force is available to bend the card it slips past the gate and into view, obscuring the preceding picture. These coin-enabled devices were found in arcades in the late 19th and early 20th century and were operated by the viewer using a hand crank. These devices can still be seen and operated in some museums specializing in arcade equipment.
The stereoscope offers several advantages:
A stereo transparency viewer is a type of stereoscope that offers similar advantages, e.g. the View-Master.
Disadvantages of stereo cards, slides or any other hard copy or print are that the two images are likely to receive differing wear, scratches and other decay. This results in stereo artifacts when the images are viewed. These artifacts compete in the mind resulting in a distraction from the 3D effect, eye strain and headaches.
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Stereoscopy is a film (non-digital) technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word stereoscopy derives from Greek στερεός (stereos), meaning 'firm, solid', and σκοπέω (skopeō), meaning 'to look, to see'. Any stereoscopic image is called a stereogram. Originally, stereogram referred to a pair of stereo images which could be viewed using a stereoscope.
3D films have existed in some form since 1915, but had been largely relegated to a niche in the motion picture industry because of the costly hardware and processes required to produce and display a 3D film, and the lack of a standardized format for all segments of the entertainment business. Nonetheless, 3D films were prominently featured in the 1950s in American cinema, and later experienced a worldwide resurgence in the 1980s and 1990s driven by IMAX high-end theaters and Disney-themed venues. 3D films became increasingly successful throughout the 2000s, peaking with the success of 3D presentations of Avatar in December 2009, after which 3D films again decreased in popularity. Certain directors have also taken more experimental approaches to 3D filmmaking, most notably celebrated auteur Jean-Luc Godard in his films 3X3D
Depth perception is the visual ability to perceive the world in three dimensions (3D) and the distance of an object. Depth sensation is the corresponding term for animals, since although it is known that animals can sense the distance of an object, it is not known whether they "perceive" it in the same subjective way that humans do.
An autostereogram is a single-image stereogram (SIS), designed to create the visual illusion of a three-dimensional (3D) scene from a two-dimensional image. In order to perceive 3D shapes in these autostereograms, one must overcome the normally automatic coordination between accommodation (focus) and horizontal vergence. The illusion is one of depth perception and involves stereopsis: depth perception arising from the different perspective each eye has of a three-dimensional scene, called binocular parallax.
Lenticular printing is a technology in which lenticular lenses are used to produce printed images with an illusion of depth, or the ability to change or move as the image is viewed from different angles.
A stereo display is a display device capable of conveying depth perception to the viewer by means of stereopsis for binocular vision.
View-Master is the trademark name of a line of special-format stereoscopes and corresponding View-Master "reels", which are thin cardboard disks containing seven stereoscopic 3-D pairs of small transparent color photographs on film. It was originally manufactured and sold by Sawyer's.
A head-mounted display (HMD) is a display device, worn on the head or as part of a helmet, that has a small display optic in front of one or each eye. An HMD has many uses including gaming, aviation, engineering, and medicine. Virtual reality headsets are HMDs combined with IMUs. There is also an optical head-mounted display (OHMD), which is a wearable display that can reflect projected images and allows a user to see through it.
A pseudoscope is a binocular optical instrument that reverses depth perception. It is used to study human stereoscopic perception. Objects viewed through it appear inside out, for example: a box on a floor would appear as a box shaped hole in the floor.
Random-dot stereogram (RDS) is stereo pair of images of random dots which when viewed with the aid of a stereoscope, or with the eyes focused on a point in front of or behind the images, produces a sensation of depth, with objects appearing to be in front of or behind the display level.
Anaglyph 3D is the stereoscopic 3D effect achieved by means of encoding each eye's image using filters of different colors, typically red and cyan. Anaglyph 3D images contain two differently filtered colored images, one for each eye. When viewed through the "color-coded" "anaglyph glasses", each of the two images reaches the eye it's intended for, revealing an integrated stereoscopic image. The visual cortex of the brain fuses this into the perception of a three-dimensional scene or composition.
Stereopsis is a term that is most often used to refer to the perception of depth and 3-dimensional structure obtained on the basis of visual information deriving from two eyes by individuals with normally developed binocular vision. Because the eyes of humans, and many animals, are located at different lateral positions on the head, binocular vision results in two slightly different images projected to the retinas of the eyes. The differences are mainly in the relative horizontal position of objects in the two images. These positional differences are referred to as horizontal disparities or, more generally, binocular disparities. Disparities are processed in the visual cortex of the brain to yield depth perception. While binocular disparities are naturally present when viewing a real 3-dimensional scene with two eyes, they can also be simulated by artificially presenting two different images separately to each eye using a method called stereoscopy. The perception of depth in such cases is also referred to as "stereoscopic depth".
Autostereoscopy is any method of displaying stereoscopic images without the use of special headgear or glasses 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 viewers' eyes are located. Examples of autostereoscopic displays technology include lenticular lens, parallax barrier, volumetric display, holographic and light field displays.
Underwood & Underwood was an early producer and distributor of stereoscopic and other photographic images, and later was a pioneer in the field of news bureau photography.
The Keystone View Company was a major distributor of stereographic images, and was located in Meadville, Pennsylvania. From 1892 through 1963 Keystone produced and distributed both educational and comic/sentimental stereoviews, and stereoscopes. By 1905 it was the world's largest stereographic company. In 1963 Department A and the Education Departments were closed down, but Keystone continued to manufacture eye-training stereographic products as a subsidiary of Mast Development Company. In 1972 Mast closed the Meadville manufacturing site.
A slide viewer is a device for looking at film transparencies or similar photographic images.
A 3D stereo view is the viewing of objects through any stereo pattern.
Stereoscopic acuity, also stereoacuity, is the smallest detectable depth difference that can be seen in binocular vision.
Stereo photography techniques are methods to produce stereoscopic images, videos and films. This is done with a variety of equipment including special built stereo cameras, single cameras with or without special attachments, and paired cameras. This involves traditional film cameras as well as, tape and modern digital cameras. A number of specialized techniques are employed to produce different kinds of stereo images.
A stereoscopic video game is a video game which uses stereoscopic technologies to create depth perception for the player by any form of stereo display. Such games should not to be confused with video games that use 3D game graphics on a mono screen, which give the illusion of depth only by monocular cues but not by binocular depth information.