Measurement System Types and Characteristics

Optical Comparators


Optical comparators are a type of optical measuring instrument. The measurement principle is similar to that of optical microscopes. The target is placed on the stage, and a light is shined on the target from underneath. This causes the target's profile, or shadow, to be projected on the screen. A telecentric optical system is used to enable accurate measurements.
Optical comparators were originally developed to inspect the outlines of targets. Models equipped with measurement functions appeared later. Some large optical comparators have screen diameters that exceed 1 m.
The following are some advantages of optical comparators.

  • Non-contact measurement of target.
  • Measurement is possible even for targets with small or complicated shapes.
  • Unlike measuring microscopes, there is no need to look through an ocular lens, which makes it possible for multiple people to perform observations at the same time.

The use of optical comparators is widespread in the inspection and measurement of items such as electronic components and precision components. Conventionally, time and effort was required for datum referencing and target positioning.

Construction and Applications

Construction and Application of Optical Comparators
Projection screen
Projection lens
Movable stage
Stage movement handles (X and Y handles)

How to Use an Optical Comparator

  1. Place the target on the stage.
  2. Position the scale on the zoomed image projected on the screen, and then measure the dimensions. The XY stage can also be used to measure the dimensions according to the amount of stage movement.
  3. Some optical comparators use a scale that is read by pinching the target. With such optical comparators, the length is read from a scale between a pair of reading lines.

Handling Precautions

  • The calibration interval for optical comparators is 6 months to 3 years.

The Latest Optical Comparators

Recent models of optical comparators are able to instantly measure dimensions without XY stage movement or focusing, enabling the measurement of many objects in a short amount of time.

For more information about KEYENCE’s latest optical comparator capable of 99 measurements in 3 seconds, click here.