| 摘要 |
An improved optical measuring instrument having an image combining mirror which reflects part of the light from one source and transmits part of the light from another source and superimposes such reflected and transmitted light over the entire surface of the mirror is disclosed. In the preferred embodiment an improved sextant is disclosed using the image combining mirror. Sextants are double reflecting optical devices which are generally used to measure the angle between a celestial object, such as the sun, the moon, or a star, and the horizon. This measurement is used primarily in navigation for determining the user's location at sea. Prior sextants split the viewing area of the horizon mirror into two fields of view: one-half horizon and one-half celestial object. The improved sextant uses a horizon mirror which combines and overlaps (superimposes) the horizon and celestial images over the entire viewing area. This is preferably accomplished by the use of a spectrally selective dielectric beamsplitter as the horizon mirror, such mirror mainly transmitting light in one spectral region and substantially reflecting light in another spectral region. The result is a horizon mirror which both splits and converges the horizon and celestial images resulting in an enlarged field of view of both the horizon and the celestial object.
|
