390 



Mr. S. D. Chalmers. 



[Jan. 3 



" The Theory of Symmetrical Optical Objectives. Part II." By 

 S. D. CHALMERS, B.A., St. John's College, Cambridge, M.A. 

 Sydney. Communicated by Professor L ARMOR, Sec. K.S. 

 Eeceived January 3, Eead January 26, 1905. 



As regards the defects which depend only on those terms in the 

 characteristic function T, that were examined in Part I,* the results 

 of that paper would justify the practice of correcting a single com- 

 ponent the hack one for astigmatism and spherical aberration, 

 provided due attention be paid to the securing, at least approximately, 

 of the condition for no distortion. 



But for the values of aperture-ratio and angular field, that obtain 

 in practical systems, the terms of higher orders in T introduce 

 important aberrations, and it is interesting to examine how far the 

 conclusions stated in Part I* are justified in the case of practical 

 systems. 



In most cases the discussion can be effected by the use of geometrical 

 relations, it being assumed as is generally the case in practice that 

 the stop is well within the focus of the single lens and that its virtual 

 image, formed by either component, is near the actual position of the 

 stop. 



In the first place we consider only those rays which lie wholly in 

 one plane. In fig. 1, (5) is the focal plane of the back component, 



FIG. 1. 



Boy. Soc. Proc.,' vol. 72, June 18, 1903. 



