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| | Advertising, marketing, and commercial imagery collections |
 | | A stereograph consists of two nearly identical images, generally photographs, exposed as a rule simultaneously and from a distance separation of approximately two-and-one-half inches, mounted on a card and viewed, with or without the aid of a binocular viewer, to produce the simulation of three dimensions. |
 | | Stereographs were manufactured and distributed commercially in large quantities by publishers for mass markets as objects of both entertainment and education, but they were also produced in smaller quantities for specialized markets. |
 | | Also, storage of the stereographs in standard document boxes posed a hazard to the material because of their size and form, especially prints on curved or "warped" mounts, which might be crushed or mishandled if filed with other items in disparate formats and sizes. |
| americanhistory.si.edu /archives/d7060h3.htm (5464 words) |
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