Stops, Pupils, and Windows
Charles A. DiMarzio · 2011
Thus far, as we have considered light propagating through an optical system, we have assumed all surfaces to be infinite in the dimensions transverse to the axis. Thus there has never been a question of whether a ray would or would not go through a particular surface. This assumption proved useful in graphical solutions where weworkedwith three rays in Figure 2.1. As we used the ray parallel to the axis, for example, we did not trouble ourselves by asking whether or not this ray passed through the lens, or was beyond its outer radius. We knew that all the rays from the object, regardless of their angle, would go through the image, so we could determine image location and magnification by using the rays for which we had simple solutions, without concern for whether these rays actually did go through the system. If there was an intermediate image, we simply started tracing new rays from that image through the rest of the system, rather than continuing the rays we used from the original object. While these assumptions allow us to determine image location and magnification, they cannot give us any information about how much light from the object will go into forming the image, nor about which parts of the object can be seen in the image. In this chapter, we address these two issues.