. Biophysical science. Biophysics. 30 Light and the Eye \1 : 2 The use of geometrical optics to describe the properties of thick lenses is outlined in Appendix B. The details will not be pursued here. Rather, it is hoped that readers interested in geometrical optics will turn to this appendix where the behavior of light at surfaces of refraction (lenses) is discussed. In the eye, the luminous energy passes through a series of curved surfaces of refraction. All of these surfaces may be approximated by sections of spheres whose centers lie on a common line. This general case has been shown to be
. Biophysical science. Biophysics. 30 Light and the Eye \1 : 2 The use of geometrical optics to describe the properties of thick lenses is outlined in Appendix B. The details will not be pursued here. Rather, it is hoped that readers interested in geometrical optics will turn to this appendix where the behavior of light at surfaces of refraction (lenses) is discussed. In the eye, the luminous energy passes through a series of curved surfaces of refraction. All of these surfaces may be approximated by sections of spheres whose centers lie on a common line. This general case has been shown to be mathematically equivalent to a single thick lens, which separates two media of different indices of refraction. It is not possible to relate the image and object distances by as simple an expression as that for a thin lens, such as Equation 10 of Appendix Object Image Figure I. A thick lens immersed in different media on its two sides. Fx and F2 are focal points. Note that Fx does not equal F2. The principal points are H± and H2, and the nodal points are Nx and N2. Rays a, b, and c are drawn as in Fig- ures B-6 and B-7 of Appendix B. However, six cardinal points completely specify the lens action. These consist of two focal points, two principal points, and two nodal points. This general case is illustrated in Figure 1. The cardinal points are denned in Figure 1; they will be used in the next section to describe the eye. The strength of a lens (or its power), L, is defined as the reciprocal of the focal length / measured from the corresponding principal plane; that is 'V (3) When/is measured in meters, L will be expressed in diopters. A lens with a shorter focal length can produce a real image for closer objects than a lens with a longer focal length. Thus, the lens produces a greater algebraic change in curvature of an incident light front. In this sense, a lens of shorter focal length is indeed stronger. In any case, increasing the radius of curvature of a converging su
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