| 摘要 |
In a viewer for vehicles, machines, apparatus and other various equipments, including an optical element, which is capable of viewing a certain range of visual field through an opening of a case by using the optical element, at least two openings are formed in the case and a mirror arranged therein is capable of being in or out of the visual field including at least the two openings, thereby changing the visual field. A Fresnel concave lens with or without a refractive prism attached thereon is put in each opening. The optical element comprises the Fresnel concave lens, the refractive prism and the mirror.
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