0227
   OPTICAL MICROMETER THEODOLITE  
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  Surveying Instrument Collection 

Maker

Carl Zeiss, Oberkochen, Germany

Model

Th 2

Serial Number

79349

Dimensions

Telescope length 155 mm, Height 315 mm

Image

Zeiss Th 2 Micrometer Theodolite

Description

This Zeiss Th 2 one-second optical micrometer theodolite is a highly accurate instrument featuring the unique "ball-and-socket" levelling system. Fields of application include precise angular measurement for traversing, first and second-order triangulations, plumbing, distance measurement with subtense bar and establishing astronomical positions.

Some of the features of the theodolite include: combined coarse-fine focusing drives, coaxial clamps and fine drives, automatic vertical circle indexing system featuring an X-type pendulum compensator, erect telescope image, convenient carrying handle, optical plummet in alidade and a sighting collimator for rapid and convenient course sighting. The instrument also features a switch which is used for switching between the horizontal (yellow display) and the vertical (white display) micrometer images. 

The most important feature of the instrument however, is far-reaching digitisation. Of the 7 figures making up one reading, 6 appear directly in digital form, thus eliminating counting or estimation. The seventh digit is, in addition, presented by a full interval per 1".

The graduation interval for angular measurement is 20' and the micrometer interval is 1". The diameters of the horizontal and vertical circles are 100 mm and 85 mm respectively. One mirror illuminates both circles. The sensitivity of the plate level is 20" per 2 mm and the setting accuracy of the compensator is approximately 0.2". The magnification of the telescope is 30x, the diameter of the objective lens of the telescope is 40 mm and the shortest pointing distance is approximately 1.6 m.

The instrument's plastic case is fitted with a number of accessories including a plumb bob, a sunshade and a toolkit containing screwdrivers, wrenches and two adjusting pins.

History & comments

The Th 2 has been designed as a valuable and high-grade instrument. New glass types were used for the telescope and, in order to reduce adjustment problems, the type of rugged lens telescope was chosen. Similar considerations apply to the novel Zeiss X-type vertical index compensator, the optical plummet incorporated in the alidade, the system of circle reading and the device for orienting the horizontal circle.

Conservation

Plastic container

Condition

Focusing screw near eyepiece is slightly loose, and compensator is sticky and needs to be tapped before observations are taken.

Remarks

  • The "ball-and-socket" levelling system is also incorporated in the Zeiss Th 4 theodolite (included in collection)
  • Weight of instrument and container is 5.2 kg and 4.8 kg respectively.
  • Upright telescope image
  • School store no: T95
  • Catalogued by F. Pall

Dates

Catalogued in 2000.

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