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Optical theodolite and its optical design

Jun. 10, 2021

Optical theodolite is a precision optical instrument used to measure horizontal and vertical angles. It is widely used in engineering surveying, geodetic surveying and metrology. In engineering control measurement and precision engineering measurement, angle measurement mainly uses precision optical theodolite.

The optical theodolite is mainly composed of a telescope and an internal imaging light path. The telescope images distant targets at different distances to enlarge the angle of view so that they can be seen more clearly. The telescope needs to form the collimation axis, aiming at the target accurately to determine the direction of the sight line of the target. The telescope consists of an objective lens (a set of cemented lens), an eyepiece (double-convex lens and plano-convex lens), a cross reticle and a focusing lens. The objective lens and eyepiece magnify the target image. The focusing lens is used to adjust the position of the target image to eliminate parallax error.

The optical components commonly used in the internal imaging optical path include right-angle prisms, rhombic prisms, reading objectives, dial objectives, lenses, mirrors, lens groups, and mirrors. The reflective imaging optical path divides a beam of light from the reflector into two beams through a long prism. The beams enter the two ends of the dial to illuminate the reticle of the dial. Then, the light is reflected twice by the upper part of the long prism and enters the objective lens at the same time. Therefore, they are simultaneously imaged on a plane and can be separated up and down. The two upper slopes of the double rhombus prism are the imaging surfaces of the microscope.

After the light in the transmissive imaging optical path enters from the mirror, it is refracted by the prism and penetrates the left end of the dial. Then the original reticle width is maintained by the lens group. The image is only rotated by 180°, and the image is formed on the vertical plane of the right-angle prism. Two pairs of optical wedges are placed between the objective lens and the imaging surface to form a micrometer.

Focusing of telescope and elimination of parallax

The telescope is used to accurately sight the target. For this reason, the image of the target in the telescope must be clear and the image must be on the cross reticle. Before observation, the focus ring of the telescope should be rotated to make the target clearly imaged on the cross reticle. This process is focusing or aiming.

General technical requirements

There should be no water, oil, dust, scratches, mildew spots and pits on the surface of the optical elements. There should be no degumming on the glued surface. There should be no peeling corrosion on the coating surface. There is sufficient brightness in the field of view of the telescope and the reading microscope. The brightness is uniform.

In order to ensure accurate measurement results, the optical theodolite must use high-precision optical components to ensure that the light is transmitted following the optical design. CLZ Precision Optics Co., Ltd. specializes in the production of high-precision spherical lenses, optical mirrors and optical prisms. According to the optical design, the optical components can be coated with single layer magnesium fluoride coatings, high reflection all-dielectric coatings and protective or enhanced coatings. If you need related optical components, please contact