. Physiological optics : being an essay contributed to the American encyclopedia of ophthalmology . tly all quan-tities are considered positive when measured from left to right, andnegative when measured from right to left, the pole A being the pointfrom which all measurements are made. Other conventions as toalgebraic signs are also in vogue and the reader is often bewilderedand at a loss because of them and because of the lack of uniformityof symbolic optical nomenclature. The refractive power of a curved surface depends, then, upon its 10 PHYSIOLOGICAL OPTICS curvature and the relative refr
. Physiological optics : being an essay contributed to the American encyclopedia of ophthalmology . tly all quan-tities are considered positive when measured from left to right, andnegative when measured from right to left, the pole A being the pointfrom which all measurements are made. Other conventions as toalgebraic signs are also in vogue and the reader is often bewilderedand at a loss because of them and because of the lack of uniformityof symbolic optical nomenclature. The refractive power of a curved surface depends, then, upon its 10 PHYSIOLOGICAL OPTICS curvature and the relative refractive index of the two bounding focal length depends upon the refractive power. 3. In Fig. 2 (a and o), RR is the principal or refracting plane atwhich all refraction is assumed, to within second order effects, tooccur. The point C, which is the center of curvature of the surfaceDA, is also the optical center (or single nodal point of this system)since any ray which passes through this point suffers no refractionor lateral deviation. In Fig. 2(a) the incident light is parallel to the. Fig. 2.—Illustrating the Eefraction of Parallel Kays by a Curved Surface giving:(a) Anterior Focus, (b) Posterior Focus. principal axis in the denser medium of index n2 and upon emergenceinto the less dense medium, index nx, is refracted so as to meet at thepoint FA. FAA is the anterior focal distamce. In a similar manner,parallel light entering from the rarer medium will be focused in thedenser medium at FP. FFA represents the posterior focal distance. FAand FP are the anterior and posterior focal points respectively. If, then, the incident light in the rarer medium be regarded as parallel and hence coming from infinity, the term becomes zero and, therefore, the general law of conjugate foci which reads nx n2 n2 — nx f, f2 11 PHYSIOLOGICAL OPTICS becomes n2 n2 — nx f2 r and the posterior principal focal length n2 r n3 r Fp = = + r. n2 — nx n2 — nx In like manner, when paralle
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