MICROSCOPE OBJECTIVE CORRECTIONS 



323 



The cross section of a typical achromatic 4-mm objective is shown in 

 Fig. VIII-9. It has been designed so that its blue image (F light, 



-{0.96 



T ----pt0.99 



3.937S | 

 ^ 3.965.R 



Fig. VIII-9. Section of a 4-mm achromatic microscope objective showing the 

 position of the focal points for B (blue light, X 4861.4 A) and R (red light, X 6562.8 A) 

 and the values of the equivalent focal lengths for these wavelengths. The 

 blue image is magnified more than the red image, and the ratio of the magnifica- 

 tion of the blue image to the magnification of the red image is chromatic difference 

 of magnification. Here 



Jr — 

 M R = 



3.965 and f B = 3.937. 

 D + 0.96 



Magnification is M. 



3.965 



D + 0.99 



45.0, M B = = 45.3 



3.937 



45.3 

 45.0 



= 1.0065 



Chromatic difference of magnification is 0.65 per cent. (By courtesy of Bausch and 

 Lomb Optical Company, Rochester, New York.) 



o ° 



X 4861 .4 A) is 0.65 per cent larger than its red image (C light, X 6562.8 A) . 

 Its chromatic difference of magnification is said to be 0.65 per cent. The 

 image formed by such an objective is excellent in every respect except 



