Transfer Function Analysis

Abstract

In the last chapter, imaging performance in an optical imaging system is analysed by a point spread function for a thin lens, which is the image of a single point object. While this method is easily understood, it sometimes lacks an insight into an imaging process. In this chapter. an analysis based on the concept of the transfer function is given for an imaging system. The transfer function method gives a physical insight into image formation in an optical imaging system. The function of an optical imaging system such as a microscope is to provide a magnified image of an object in which details are too fine to be seen by naked eye. It is desirable that an imaging system should have an ability to reproduce the details in an object. As we will see, an optical imaging system is a low pass filter which transmits only low spatial frequencies corresponding to slow variations in an object. The fine details of the object are represented by high spatial frequencies. These high spatial frequencies may not be imaged because an optical system has a cutoff spatial frequency. Further, the efficiency with which the harmonic (spatial frequency) components are transmitted are dependent on optical systems. These properties can be analysed in terms of the Fourier transformation.