GB1394453A - Optical instruments - Google Patents

Abstract

1394453 Surveyor's level RANK ORGANISATION Ltd 17 May 1973 [26 May 1972 and 17 Jan 1973] 24961/72 and 2463/73 Heading G1F [Also in Division G2] A reflecting system for an instrument e.g. a surveyor's level comprises a rigid, transparent element 1 having a plane upper surface on which rests a film 4 of transparent liquid, the film 4 being thick enough to be affected by gravity. Means 3 direct light 2 through the element 1 so that it is reflected at the upper surface 6 of the liquid film 4 to provide a reflected beam 5. The reflected beam 5 is preferably reflected back through the system to cancel the effect of changes in thickness of the liquid film 4. In one embodiment Fig. 5 an entrance ray 510 is incident normally on a first prism 511, is reflected at faces 512, 514 and passes through a second prism 515 and the base 518 of a cell 517 containing liquid 519. The light is reflected at the under face of the upper surface 520 of the liquid and is returned to the prism 515 which has two faces (not shown) which return the light parallel to but laterally spaced from the incoming beam. This reflected beam passes through a prism 523 being reflected at face 522 to a plate 521 so as to be reflected out normally to face 524 of prism 514. A beam-splitting device is preferably placed in the path of the incident light. A graticule and/or eye piece lens may be provided for viewing the energent light, or a signal may be generated by the position and/or inclination of the energent beam e.g. for automatic position control. Polarizers may be placed in the path of the incident beam and the returning secondary reflected beam. The reflecting surface which returns the light through the system may rotate the plane of polarization through 90 degrees.