ABSTRACT
Most equipment used for measuring the OTF of imaging systems (i.e. electro-optical as well as pure optical systems) is of the type where the intensity distribution in the image of a known incoherently illuminated object pattern is measured and the OTF determined from this. It is convenient to consider equipment that measures OTF in this way, as made up of a number of basic units as illustrated in block diagram form in figure 4.1. A unit is required to produce the illuminated test pattern, another is 116required to measure the intensity distribution in the image of the test pattern generated by the test piece and finally some form of mechanical fixture is required to hold these units and the test piece in the correct positions relative to each other for making the measurements. In addition to this one may require lenses, other than the test piece, to relay images to convenient positions. For example, many lens systems are designed for forming images of distant objects (i.e. objects theoretically at infinity) and a special lens (the collimator) will be required to make the test pattern appear to come from infinity. A convention has grown up for the nomenclature of the units that together make up an OTF/MTF test facility and this will be found reproduced in several national and international standards (see [1, 2]). These conventions are used wherever applicable in this book and the purpose of this section is to introduce them to, and define them for, the reader. Basic units that make up OTF/MTF equipment for testing an optical system. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203736296/78996aa1-9954-42b8-8584-bea67973a5c0/content/fig4_1.tif"/>
