| 摘要 |
<p>Here is disclosed a datum beam projecting apparatus for use with a surveying equipment to project light rays emitted from a light source as the datum beam through a projecting lens system, wherein the apparatus uses a plane-parallel glass serving to compensate a tilt of the datum beam, thereby to maintain a direction of the projected datum beam constant with respect to a tilt of the apparatus and the above-mentioned plane-parallel glass is tiltably located in an optical path defined between the light source and the projecting lens system so that a following relationship may be satisfied : tan beta = K tan alpha where alpha represents a tilt of the apparatus, beta represents a tilt of the plane-parallel glass and K is a constant. With the apparatus of this invention constructed as mentioned above, a tilt of the datum beam can be effectively compensated merely by tilting the plane-parallel glass by the angle beta corresponding to a predetermined times the tilt alpha of the apparatus, so that the complicated arrangement comprising concave lenses, prisms etc. usually required for compensation can be eliminated and thereby not only the structure can be simplified but also the apparatus of a reliable precision can be obtained at a reasonable cost.</p> |
