| 摘要 |
An optical system is shown for use with an image source to provide an enlarged virtual image with minimal geometric distortion. The optical system is suitable for generating a virtual image of text information in small font sizes, such as 8 point font or 10 point font, where the small font size text can be readily discerned. The optical system includes a prism having positive power wherein the total power is distributed among the prism's optical surfaces in a balanced manner and wherein the power across each surface is balanced as well. The prism employs a combination of rotationally asymmetric aspheric surfaces and a rotationally symmetric aspheric reflector so as to provide an extremely high quality virtual image across the entire width thereof, i.e. in the edge or peripheral portion of the image as well as in the central portion of the virtual image. The prism may be used alone or in combination with a thin corrector lens that not only corrects for subtle distortions but also protects the prism from contaminants.
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