{
  "patent_number": "US 2189285",
  "country": "US",
  "title": "How the View-Master 3D Image Viewer Works",
  "original_title": "Stereoscopic viewing device",
  "summary": "A 1939 invention for a handheld device that uses two offset images to create the illusion of depth, famously known as the View-Master.",
  "what_it_does": "The device uses a pair of lenses and a rotating disc containing pairs of translucent film images. When the user looks through the lenses, the device aligns the left and right images to create a stereoscopic effect, where the brain perceives a single 3D image. The mechanism includes a lever or trigger that advances the disc to the next pair of images, allowing the user to view a sequence of 3D scenes without removing the disc.",
  "what_it_does_not_cover": [
    "Does not cover digital 3D displays or liquid crystal shutter glasses.",
    "Does not cover projection-based 3D systems that require a screen.",
    "Does not cover devices that use non-translucent (opaque) paper prints."
  ],
  "filed": "1939-01-20",
  "granted": "1940-02-06",
  "expires": "1959-01-20",
  "status": "expired",
  "holder": "Individual",
  "holder_url": "https://patentbrief.org/company/individual",
  "inventors": [
    {
      "name": "Wilhelm B Gruber",
      "url": "https://patentbrief.org/inventor/wilhelm-b-gruber"
    }
  ],
  "times_cited": 28,
  "tags": [
    "consumer_electronics",
    "mechanical"
  ],
  "abstract": null,
  "url": "https://patentbrief.org/patent/us/2189285/view-master-stereoscope",
  "markdown_url": "https://patentbrief.org/patent/us/2189285/view-master-stereoscope/md",
  "google_patents_url": "https://patents.google.com/patent/US2189285",
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}