Reading microscope
Reading microscopes are short, weakly magnifying microscopes with which graduated circles can be read precisely. They have been used since around 1800 for all precise angle measurements , as they are necessary in astronomy for meridian circles or in geodesy for theodolites and total stations .
Older measuring instruments still have open reading microscopes, which are attached in pairs at opposite points on the measuring circle. Modern theodolites only have a reading microscope directly next to the telescope, in whose field of view the diagonal points of the partial circles are reflected together by a folded beam path. This means that the measurement can be carried out very quickly and with only a low error rate. Since the 1990s, however, opto-electronic reading with immediate digital storage has become increasingly popular .
With large universal and passage instruments , the reading can be accommodated in a closed, moisture-proof and dust-proof housing, while with large astronomical telescopes the beam path is often directed to a fixed point, comparable to the placement of a Coude focus .