The Collaborative International Dictionary
Stereoscope \Ste"re*o*scope\, n. [Stereo- + -scope.] An optical instrument for giving to pictures the appearance of solid forms, as seen in nature. It combines in one, through a bending of the rays of light, two pictures, taken for the purpose from points of view a little way apart. It is furnished with two eyeglasses, and by refraction or reflection the pictures are superimposed, so as to appear as one to the observer.
Note: In the reflecting stereoscope, the rays from the two pictures are turned into the proper direction for stereoscopic vision by two plane mirrors set at an angle with each other, and between the pictures. In the lenticular stereoscope, the form in general use, the eyeglasses are semilenses, or marginal portions of the same convex lenses, set with their edges toward each other, so that they deflect the rays coming from the picture so as to strike the eyes as if coming direct from an intermediate point, where the two pictures are seen apparently as one.
Douglas Harper's Etymology Dictionary
Wiktionary
n. an instrument used for viewing pairs of stereoscopic photographs
WordNet
n. an optical device for viewing stereoscopic photographs
Wikipedia
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.
Usage examples of "stereoscope".
The centre-table had two or three gilt-edged books lying carelessly about on it, and some prints and a stereoscope with stereographs to match, chiefly groups of picnics, weddings, etc.
Moving the stereoscope viewer away from her eyes, she realized with a start exactly why.
She would not touch the naughty stereoscope again, but there was a pile of journals on the sideboard.
She did not want to see him as naked as the men in those naughty stereoscope pictures, or to have him do unspeakable things to her as they were doing to each other in the pictures.
If you could have seen the old, funny twinkle in her eye, when I found her with the stereoscope, you would have thought she was a real, live Chicken, sure enough.
The stereoscope was a brand-new invention, fashioned of maple wood and glass.
Lifting the stereoscope to his eyes, Marcus examined the view of the Colosseum in Rome with undue concentration.
Already latent inside me, like the future 120 mph serve of a tennis prodigy, was the ability to communicate between the genders, to see not with the monovision of one sex but in the stereoscope of both.
When he had done so she motioned to the portable stereoscope which lay inside.
But though his Silvia was affectionate and amiable enough to let him put the stereoscope over her muzzle, yet she would not look through it, but kept turning her head to lick his hand, and it was plain to him that now she had quite forgotten the use of the instrument.
He walked over by the lookouts at stereoscopes and radar tanks and peered up at the star-flecked blackness.
At the turn of the century, people purchased viewscopes and stereoscopes that let them see foreign pictures.
The centre-table had two or three gilt-edged books lying carelessly about on it, and some prints and a stereoscope with stereographs to match, chiefly groups of picnics, weddings, etc.
I got the photographs and the reports from the pathologist and house surgeon that afternoon, and after my consultations were over for the day I sat down with the photographs at the stereoscope.
He walked over by the lookouts at stereoscopes and radar tanks and peered up at the star-flecked blackness.