What is an Autocollimator?

An autocollimator is an optical instrument that is used to measure small angles with very high sensitivity. As such, the autocollimator has a wide variety of applications including precision alignment, detection of angular movement, verification of angle standards, and angular monitoring over long periods.

Principles of Operation

The autocollimator projects a beam of collimated light. An external reflector reflects all or part of the beam back into the instrument where the beam is focused and detected by a photodetector. The autocollimator measures the deviation between the emitted beam and the reflected beam. Because the autocollimator uses light to measure angles, it never comes into contact with the test surface.

Digital vs. Visual Autocollimators

Digital Autocollimators

Digital autocollimators use an electronic photodetector to detect the reflected beam. Micro-Radian autocollimators take advantage of the latest detector technology including advanced silicon-based photodetectors and germanium-based detectors. The detector sends a signal which is digitized and processed using proprietary DSP-based electronics. The processing creates a calibrated angular output which is traceable to the Swiss Federal Institute of Metrology (METAS).

Digital autocollimators are available as stand-alone bench top models, as USB-based models designed for use with a PC and as optical-head-only models designed for direct integration into OEM systems. Available outputs include a touchscreen LCD display on the bench top models as well as a combination of USB 2.0, RS-232, and analog signals.

The exceptional accuracy and high resolution of digital autocollimators make them suitable for applications including the calibration of rotary tables, the verification of angle standards, and for remote or long term angular monitoring operations. Additional uses include measurements of flatness or straightness and providing angular feedback in servo-controlled systems.

Click here for a selection of Micro-Radian bench top digital autocollimators or click here to view the PC-based digital autocollimators. Please contact us to discuss your particular application.

Digital Autocollimator Diagram

Digital Autocollimator Diagram


Visual Autocollimators

Visual autocollimators rely on the operator's eye to act as the photodetector. Micro-Radian visual autocollimators project a pinhole image. The operator views the reflected pinhole image(s) through an eyepiece. Because the human eye acts as the photodetector, resolution will vary among operators. Typically, people can resolve from 3 to 5 arc-seconds. Because the human eye is able to discern multiple images simultaneously, visual autocollimators are suitable for measuring multiple surfaces simultaneously. This makes them ideal alignment instruments in applications like aligning laser rod ends or checking parallelism among optics. Visual autocollimators can also be equipped with an eyepiece reticle for aid in lining up test optics to a master reference. All Micro-Radian visual autocollimators are focused on infinity, making them suitable for use at any working distance.

Micro-Radian also offers a visual autocollimator that uses a CCD camera in place of the eyepiece. The camera transmits a video signal via USB 2.0 and the images are viewed on a monitor.

Click here for a selection of Micro-Radian visual autocollimators.

Visual Autocollimator Sample Applications

Visual Autocollimator Diagram


Measurement of non-parallelism in windows, laser rod ends, and optical wedges by the two-face reflection method.


Visual Autocollimator Diagram


Measurement of squareness of an outside corner by aperture sharing.



Visual Autocollimator Diagram


Angle comparisons by aperture sharing.



Visual Autocollimator Diagram


Checking right angle prisms for angular and pyramid errors.



Specialized Autocollimators

Laser Autocollimators

Micro-Radian is the only company that manufactures autocollimators with laser light sources. Micro-Radian laser autocollimators have emitted beams as small as 1.0 mm in diameter. These specialized instruments are designed for measuring small test parts including silicon components, miniature mirrors and lenses, and fiber optic components. They are also ideal any time very low noise measurements or very long distance measurements are desired.

Servo-Controlled Systems

Micro-Radian autocollimators are available in both analog or digital "servo" versions suitable for providing high speed, real-time angular monitoring in OEM servo-feedback and servo-feedforward systems. Typically, the servo-version of the T40 or T30 optical heads are selected because of their compact, lightweight size and wide field of view. Click here for a selection of Micro-Radian analog autocollimators. Click here for a selection of Micro-Radian PC-based digital autocollimators.

Please contact us if you have any questions regarding servo-controlled systems.

Custom Requirements

Micro-Radian designs and manufactures all of its autocollimators and is very capable of making modifications to existing instruments to suit customer requirements. We are also fully capable of designing and manufacturing specialized autocollimators as the needs require.