Autocollimator

Representation of the experimental setup

An autocollimator is an optical angle measuring device for small angles.

functionality

An autocollimator measures changes in the angle of an object. For this purpose, a reflector, for example a mirror , is attached to the object . The autocollimator has a light source that emits a light beam. The light beam is directed onto the mirror, reflected by the mirror and focused on a detector. If the object tilts, the focus moves to the detector.

With the help of this shift and the focal length of the optics used, the angle of the mirror can now be precisely determined. This is used to approximate what is a good approximation for the small angles to be measured . It results: ${\displaystyle d}$ ${\displaystyle f}$ ${\displaystyle \alpha }$ ${\displaystyle \tan(\alpha )}$ ${\displaystyle \alpha }$

${\displaystyle \alpha =\arctan \left({\frac {d}{2f}}\right)\approx {\frac {d}{2f}}}$

A CCD array or a PSD , for example, is used as a detector . There are also analog autocollimators in which the position of the focus is determined with reading optics.

So that the reflected light beam is not shaded by the light source, a beam splitter is usually provided with which the light beam coming from the light source is deflected onto the mirror.

Of course, only small angles can be measured in this way, since the light beam has to be reflected back into the optics of the autocollimator.

See also

• Beam splitter
• Autocollimation

Web links

• Basics of autocollimators (accessed on August 22, 2020)
• Weck, Manfred: " Machine tools 5: Metrological investigation and assessment, dynamic stability" , 7th edition, 2006