Eyepiece micrometer
As ocular micrometer into which is the eyepiece of a telescope built-in or microscope micrometer referred to are possible with the fine measurements of observed objects. De facto, these are angle measurements in the field of view of the optical instrument, although - depending on the specific task - lengths, positions or distances of the object are also calculated from them.
In the eyepiece micrometer, the thread network ("reticle") is mounted in the focal plane of the objective and is connected to a mechanical or optical micrometer screw with which the current position of the plate is measured relative to a defined reference direction.
If the now movable thread is set to the target by the observer or by means of a sensor or (in the case of a moving target) is kept in coincidence with it, then
- a more precise measurement or a whole series of measurements possible for fixed targets ,
- in the case of moving targets, a time series of the current position of the object relative to the sighting axis of the telescope.
A simple eyepiece micrometer was developed by Olaf Römer around 1670 for the Paris observatory . Micrometer The “impersonal” or recording micrometer came into astronomy in the 19th century , with the help of which the personal equation (the reaction time) of the observer could be greatly reduced. So were astronomical lengths - and timings to some milliseconds possible, as well as in determining accurate star positions .
For astronomical latitude determination , the Horrebow-Talcott method was developed around 1900 to monitor the rotation of the earth ( international latitude service ) . Here are pairs of stars selected every few minutes in almost the same zenith distance culminate, but north and south of the zenith. The difference between the zenith distances must be smaller than the field of view so that the 2nd star can only be seen by swiveling the instrument by 180 °. It is measured with the eyepiece micrometer (adjustable horizontal thread), while a horrebow bubble clamped to the telescope ensures the constant inclination of the sighting axis .
See also
- Crosshair eyepiece
- Object micrometers in microscopy
- Circular micrometers in astronomy
- Reticle for marking in the weapon telescope image
Literature and web links
- Leitz eyepiece screw micrometer
- Karl Ramsayer : Geodetic Astronomy , Volume IIa of the Handbook of Surveying , 900 p., JBMetzler-Verlag, Stuttgart 1969
- Length measurement with the microscope (objective and object micrometer)
- Albert Schödlbauer: Geodetic Astronomy. Basics of observation instruments . Walter de Gruyter, 2000, ISBN 978-3-11-015148-0 , p. 451–452 ( limited preview in Google Book search).
- University of Bonn, Geodetic Astronomy