Autocollimator

An autocollimator is an optical angle encoder for small angles.

Operation

An autocollimator measures angular changes of an object. To a reflector mounted on the object, such as a mirror. The autocollimator has a light source that emits a light beam. The light beam is directed onto the mirror, is reflected from the mirror and focused onto a detector. Tilting the object, moves the focus on the detector.

By means of these displacement d and the focal length f of the optical system used, the angle of the mirror can then be precisely determined. It is approximated by, which is a good approximation for small angle to be measured. It follows that:

As a detector array, a CCD or a PSD is used, for example. There are also analog Autocollimators in which the position of the focus is determined with a Ableseoptik.

So that the reflected light beam is not shaded by the light source, a beam splitter is provided for in the rule by which the incoming light beam from the light source is deflected at the mirror.

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