| 摘要 |
A door viewer includes two prisms (9,9') e.g. of rectangular isosceles triangle shape in cross section, whose hypotenuse surfaces abut horizontally, a front convex lens (4), an intermediate plano-convex lens (4') and a plano-convex eyepiece lens (4"). The front convex lens (4) may have a front concave surface and a rear convex surface to correct chromatic aberration. The convex surfaces of the intermediate and eyepiece lenses (4',4") are positioned face to face with each other to correct barrel distortion. The viewer may cast an image onto an optional ground glass screen formed on or provided abutting the eyepiece lens (4").
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