Most optical design softwares rather rely on the concept of encircled energy which is the ratio of the energy (integral of PSF) within a given disk to the total energy of the PSF. We can compute the rms of the PSF but in practice this is rarely done. Just like we computed the rms value of the geometrical spot size, we can extract information from the PSF of Figure 1 through simple mathematical operations. This is exactly what I am going to address in this post. We can compare the PSF of two systems and visually tell if one seems to be better than the other (tighter psf equals better resolution) but we dont have a single number that we can use for automated analysis, such as the rms of the geometrical spot size that we introduced earlier. This however still lack some of the quantitative aspect we were looking for. Figure 1 Example of Point Spread Function (PSF) You can review the various normalization methods in our previous post. The amplitude of the plot does not really matter and different normalization rules are often applied such as normalizing by the integral of either the plot or the cross section. An example of PSF is given in Figure 1 with the full image on the left and a cross section on the right. It shows how an infinitely small source point (eventually in the form of a collimated beam) is spread on the detector surface. The point spread function can be seen as the impulse response of the optical system. I then introduced a more quantitative way to assess image system quality through the geometrical spot size but it lacked a complete description of the diffractive effects of light, reason for which I then introduced the concept of diffractive point spread functions. In previous posts I mentioned the fact that image simulations, despite being a great visual communication tool, are not suitable for system analysis mainly because they are not quantitative enough about the system aberrations. Published: | Categories: Tutorialsand Optics.
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