Analactic
The term analactic (ancient Greek for not deviating ) is used in the optics of geodetic telescopes and refers to the reference point for measurements.
The analactic point of a measuring telescope is the point to which the distances determined by angle measurement refer. With the astronomical telescope it is in the focal point of the lens. Because this i. A. does not have the vertical rotational axis of the instrument ( the vertical axis in the theodolite located), but significantly behind, the difference must
- be deducted for optical distance measurement, or
- the beam path in the telescope can be changed constructively.
With the analactic telescope , the analactic point is exactly above the vertical axis of the measuring instrument. One achieves this
- according to the Ignazio Porro system with an additional converging lens between the objective and the crosshair (the focal plane of the eyepiece). The beam path thus corresponds to a Huygens eyepiece ;
- in modern theodolites by a multiple lens system in which the focusing lens (which also acts as an inverting lens for an upright image) takes on the main role for the position of the beam intersection.
literature
- Franz Ackerl : Geodesy and Photogrammetry . 1st part: instruments and methods of surveying . Georg Fromme & Co., Vienna 1950, chapters 16.5 and 35.
- Heribert Kahmen: Surveyors . 19th edition, De Gruyter 1993.
Individual evidence
- ↑ word formation after allaktos (different) cf. Wilhelm Gemoll : Greek-German school and manual dictionary . G. Freytag / Hölder-Pichler-Tempsky, Munich / Vienna 1965. and parallactic .
- ↑ The lexicon of optics defines it as follows: the point on the optical axis of a telescope from which the distance to objects of the same image size is proportional to their actual size. When using the telescope for distance measurements, the a. P. coincide with the intersection between the vertical axis of rotation (standing axis) and the optical axis.