autocollimators

Autocollimators are optical instruments used to measure very small angular displacements and to aid in the alignment of components on optical benches, machine tools, and telescopes. They operate by projecting a narrow, collimated beam of light toward a reflective target and observing the returned image or spot. Modern autocollimators may be purely optical devices or electronic systems that detect the return with a sensor.

The working principle is straightforward: a collimated beam from the instrument is directed at a plane mirror or reference surface. If the target is exactly normal to the beam, the reflected light follows the same path back through the optical system and the image of the reticle is stationary. Any angular deviation between the instrument axis and the target causes the reflected spot to move across a reticle or onto a detector. The observed displacement is related to the angle by the instrument’s geometry, allowing high-precision angular measurements, typically at the arcsecond level for high-end units.

Autocollimators come in optical and electronic forms. Traditional optical autocollimators use a telescope, reticle, and a mirror target, while electronic versions replace the viewing eyepiece with a camera or photodetector array and software to report angular values. Configurations may be single-axis or multi-axis, and some systems employ a corner-cube or retroreflector to improve return signal.

Applications include alignment of machine tools and optical assemblies, verification of flatness or straightness on surfaces, telescope and mount alignment, and calibration of angular encoders. Proper calibration and temperature-stable setups are important to achieve the best accuracy.