Basics of the Optical Comparator 130

This class explains the principles of optical inspection and describes the components of the optical comparator.


Class Name:
Basics of the Optical Comparator 130
This class explains the principles of optical inspection and describes the components of the optical comparator.
Number of Lessons:
Additional Language:

Class Outline

  • Objectives
  • What Is Optical Inspection?
  • Light Waves
  • Non-Contact Measurement
  • Magnification
  • Types of Optical Measuring Instruments
  • What Is the Optical Comparator?
  • Parts of the Optical Comparator
  • The Mirror System
  • The Viewing Screen
  • Charts
  • Types of Optical Measurements
  • Types of Optical Comparators
  • Advantages of the Optical Comparator
  • Disadvantages of the Optical Comparator
  • Summary


  • Define optical inspection.
  • Describe the properties of light waves.
  • Describe the benefits of non-contact measurement.
  • Describe the purposes of magnification.
  • List common optical measuring instruments.
  • Define the optical comparator.
  • Identify the parts of the optical comparator.
  • Describe how mirrors affect a light path.
  • Describe the properties of the viewing screen.
  • Describe the purpose of charts.
  • Identify the different measurements taken on the optical comparator.
  • Identify the different types of optical comparators.
  • Describe the advantages of an optical comparator.
  • Describe the disadvantages of an optical comparator.

Job Roles


  • MSSC Quality Practices and Measurement


Vocabulary Term Definition
angle A figure formed at the intersection of two lines.
angle measurement A type of measurement method that compares an unknown angle with a known angle. Many charts are available with different angle markings.
ball bearing A rotating support containing metal balls that is placed between two parts allowing them to move easily with little friction.
caliper A measuring device on the optical comparator that has a scale and is used to measure the length of a part.
chart A piece of translucent paper or frosted glass that contains measurement information for comparison. Charts can quickly determine if a part fits within tolerance specifications.
collimator lens A type of lens that produces parallel beams of light. The collimator lens projects intense light toward the part.
comparison measurement A type of measurement method that compares an unknown measurement with a known measurement. Comparison measurement allows inspectors to accept or reject a part quickly.
contoured surface Any curved surface or feature differing from a straight line.
direct measurement A type of measurement method that allows an inspector or operator to use a hand-held instrument to directly measure a part feature on the optical comparator screen.
electron A negatively charged particle that orbits the nucleus of an atom. Electrons emit energy in the form of light.
fixture A dedicated workholding device used to locate and hold a part during machining or inspection.
ground glass The finely grained glass material used to make a viewing screen. Ground glass produces a fine texture that provides a bright, clear image for inspection.
lamp enclosure The part on the optical comparator that covers the light source. The lamp enclosure protects the optical comparator from heat damage.
laser A type of instrument that emits an intense, narrow beam of light to measure part features. Laser light yields very accurate and consistent measurements.
lenses A shaped piece of glass with two opposite curved surfaces used in an optical instrument to form an image by focusing light.
light The energy emitted from electrons. Light is what makes vision possible.
light source The place where light originates in an optical instrument. The light source is usually very powerful and must be protected by an enclosure.
magnification The enlarged view of an object by an optical instrument. Magnification allows you to see details that you cannot see with the naked eye.
measuring microscope An instrument that magnifes part features for direct measurement. The measuring microscope is much smaller than the optical comparator.
mirror A smooth piece of glass that forms images by reflection. Mirrors are used in optical comparators to redirect light.
non-contact measurement A measurement method that inspects a part without actually touching it. Non-contact instruments often use light to inspect a part.
optical comparator An instrument that projects a magnified image of a part feature onto a screen for inspection. It is also known as an optical projector.
optical inspection A method of inspection that uses sight, light, and magnification to inspect the features of a part.
optical projector A common term for the optical comparator.
overlay chart A type of chart made of translucent paper that contains an outline of a specific part and its dimensions. An overlay chart is placed over the viewing screen and checks if a part fits in acceptable tolerance zones.
projection magnification lens A type of lens that magnifies an illuminated image onto the optical comparator screen. Projection magnification lenses come in a variety of different magnifications.
projector screen Another term for a viewing screen.
radii The distance from the center of a circle to a point on its circumference. The plural term for "radius" is "radii."
range The limit of measurement values that an instrument is capable of reading. The dimension being measured must fit inside the range of the instrument.
screen ring A ring consisting of markings around its edge for measuring angles. The screen ring fits around the entire viewing screen.
slide A moving piece on the staging table that allows a part to move to different positions. Slides allow the user to position the part so its shadow falls in the correct location on the optical comparator screen.
staging table The surface that supports the part on an optical comparator. The staging table has slides that move the part in different positions to change its view.
standard A unit of measurement to which other units are compared. The length of a light wave is used as the ultimate standard for measurements of length.
tolerance The unwanted but acceptable deviation from a desired dimension. Increasingly accurate dimensions require tighter tolerances.
translucent paper A type of paper that permits the passage of light. Overlay charts are made of translucent paper.
viewing screen A round, glass surface on the optical comparator that displays a magnified image of a part. The viewing screen is also known as a projector screen.
vision system An instrument that uses a type of video camera to magnify part features for inspection.
watt A measurement that describes the intensity of light or power.
wave A shape or outline that has successive curves. Light travels in waves.