The Abbe comparator principle is a method for determining length or distance measurements using optical comparison measurement. It was developed by Ernst Abbe, a German physicist and optician of the 19th century.
The Abbe comparator consists of a fixed measurement object that serves as a reference, and a movable measurement object that is to be measured. Both objects are arranged in a microscope and are illuminated by a common light source.
The light is focused by a condenser lens and reduced to a narrow beam by a diaphragm. This beam passes through the measurement object and is reflected or transmitted. The reflected or transmitted light passes through another lens and is magnified in an eyepiece.
The goal of the Abbe comparator is to measure the difference between the length of the reference object and the length of the measurement object. The measurement object is first roughly approximated to the reference length and then finely adjusted by moving the measurement object in the micrometer range. This continuously changes the distance between the two objects until no difference is visible between the two objects.
To achieve high accuracy, multiple measurements are performed and the average is calculated. The Abbe comparator principle can be used to determine length measurements with an accuracy of about 0.1 micrometers.
The Abbe comparator principle is commonly used in precision manufacturing and in the calibration of measuring instruments. It is a proven method that still plays an important role despite the advances in measurement technology.