GB804594A - Improvements relating to optical instruments - Google Patents

Abstract

804,594. Optical apparatus. FILOTECNICA SALMOIRAGHI S. P. A. Feb. 6, 1956 [Feb. 9, 1955], No. 3650/56. Addition to 761,804. Classes 97(1) and 97(2) An optical instrument, other than an automatic surveying level, for providing a line of sight which is accurately horizontal or at a predetermined angle to the horizontal, which has part of its optical axis substantially vertical and has a sighting reticle and an objective system which forms an image of the observed field on the recticle, has the reticle or the objective system pedularly suspended by the system set forth in Claim 1 of the parent Specification for correcting for the effects of small movements of the instrument. Thus the telescope system of cathetometer may be constructed as shown in Fig. 4 of that Specification. Fig. 2 shows the application to the scale reading system of a theodolite the scale 9 of which is observed through an eyepiece 12, containing a graticle, and suspended objective 10 using reflecting prisms 10a, 11. The scale is illuminated by light from a mirror 14 passing through a plate 14, lens 13 and prism 13a on to the rear of the scale. A small circle engraved on the plate 14 is imaged by the lens 13 on the scale and, by its position in the field of view of the eyepiece, indicates whether the errors of levelling of the instrument are within the limits which can be compensated by the suspension of the objective 10 or whether the instrument must be more accurately levelled. A similar system, comprising an eyepiece with its axis horizontal, a reflecting prism and a suspended objective with its axis vertical, is described as fitted into the base of a theodolite for viewing downwards to act as an optical plummet. Fig. 4 shows a device for checking the flatness of a surface on which its base 20a is placed. It comprises an objective 24, pentagonal prism 23, suspended reticle 22, a further lens system 20 a prism 19a, a fixed graticle 19 and an eyepiece 25. Movements of the image of an observed object, relatively to the graticle 22 indicate changes of level as between different parts of the surface; whereas the apparent relative displacement of the graticles indicates the inclination of any one part of the surface