1. Paraxial optics
Kohler illumination belongs to non image optics (also known as illumination optics). In image optics, due to the imaging effect of the lens, the object and image form a one-to-one conjugate relationship. According to wave optics, the image is formed by the superposition of wave front through ideal optical mirror groups. Usually, the travel of light is calculated according to the points of wave front. However, due to the huge amount of Optical lens manufacturercalculation of the propagation process of the wave front in the actual elements (only solving the Maxwell equations is a pile of differential equations), the results can not be simplified. Therefore, although wave optics can describe the propagation of light more carefully and accurately, based on the simplicity of engineering application, the current optical imaging principle is still simulated based on geometric optics theory (obviously, the conclusions obtained from the experiment are always applicable).
Therefore, the calculation of light travel path by ray in geometric optics is still continued in engineering applications. Because light is a normal vector perpendicular to the direction of electromagnetic wave oscillation and can represent the direction and position of light at the Optical lens manufacturersame time, an object can be regarded as a series of point sources. In a known optical system, the relationship between the light track starting from each point of the object and its imaging position and size can be calculated. Only in imaging optics, from the generalization of the operation for a single ray to the matrix operation for a large number of rays, the essence is still ray tracing according to Snell's law.
Snell's Law:
We can see that this relationship is nonlinear. This feature directly complicates the calculation process, especially after two or three surfaces, it is difficult to specifically analyze the relationship between incoming and outgoing light rays. In the lens group with more than a dozen surfaces, multiple matrix operations with trigonometric functions will undoubtedly make this problem impossible in the era of no computer.
