There are no pure optical comparators but the instruments classed as optical comparators obtain large magnifications by the use of optical principles though mechanical magnification in these instruments contributes quite a lot for the overall magnification.
All optical comparators works on one of the following two main principles
- The use of the optical lever
- The use of enlarged image
Optical comparators are capable of giving high degree of measuring precision and owing to the reduction of moving members they possess better wear resistance qualities, than mechanical types. Also the inherent disadvantages found with the mechanical comparators, such as weight, bending properties, friction etc., are overcome by optical comparators.
Advantages of Optical Comparators
- Optical comparators have few moving linkages and hence are not subjected to friction and consequent wear and tear. This results in high accuracy of measurement.
- The scale can be made to move pas a datum line and thus have high range of measurements and no parallax error.
- The magnification is usually high.
Disadvantages of Optical Comparators
- Heat from the source of light, transformers etc., may cause the setting to drift.
- An electric supply is necessary to operate these type of comparators.
- The size of these comparators are large, and costly.
- Since the scale is projected on a screen, it is essential to use these instruments in dark room in order to take the readings easily.
- Some comparators in which the scale is viewed through an eye piece of a microscope are not convenient for continuous use.