An autocollimator is a device used to measure small angles with extreme precision. There are a number of applications for this type of equipment, especially in the sciences, where exact measurements are critical for a number of tasks. They can be used to collect observations, calibrate scientific equipment, measure experimental results, and guide telescopes and other optical equipment. Suppliers of scientific equipment and optics may carry autocollimators, and can order them by request if a customer has a specific need.

This device projects an extremely narrow beam of light at a mirror mounted on a target. The mirror reflects the light back into the autocollimator. With a digital device, the light hits a sensor that measures the deflection to determine the angle of the target. It is also possible to look through an eyepiece with a reticle, a small grid with markings, to measure the deflection manually by looking at how the position of the light has shifted on the return.

Various factors make it impossible for an autocollimator to project a beam of perfectly straight, even light, and for the reflection to be absolutely perfect. Technicians calibrate the devices to account for issues like temperature differences that may cause the light to waver slightly as it travels. This compensates for the errors created during real time measurement, and allows scientists to rely on the measurements produced by the device. The high sensitivity of these devices makes it important to regularly inspect, calibrate, and maintain them for best results.

Scientists can use an autocollimator to take measurements without actually touching a target. No physical contact is required because the device uses light to measure. This can be useful in a variety of settings where people may not want to disturb something under study. The device can also take repeat measurements of the same target over time to track movements and changes. Digital devices can be programmed to automatically remeasure and record at set intervals.

When an autocollimator is not in use, it should be covered or otherwise protected to keep the mechanism free from dust and reduce the risk of injury. These devices use lasers, and it is important to be careful around them. Someone standing in the way of the beam could experience vision damage, especially with repeat exposures. The area in front of an autocollimator should be checked and cleared before use, and personnel around the device should be trained in laser safety.