PHYSICAL ASPECTS OF IMAGE FORMATION 



55 



the pin-point source S^y The grating P, the spectra of which do not 

 penetrate into the objective Oi, is observed. Only the direct image 

 S'^) does penetrate into the objective and only a uniform illumination 



12 



8 



K = I22 



Fig. 1.71. Effect of the condenser aperture on the resolution of two pin-points of equal 

 intensity (after H. H. Hopkins and P. M. Barham). 



is visible in the image plane P'. Let us open the condenser diaphragm: 

 the hght is originated from a wide source SiS.,. The grating P is 

 obliquely illuminated by the edge of source S, and the arrangement 



•s. 



(o) 



•si 



•s. 



(b) 



Fig. 1.72. Effect of the condenser aperture on the resolution of a periodic object. 



is very similar to that in Fig. 1.62. The direct image S'^) spreads out 

 and its lower portion in Fig. 1.72(b) matches the upper portion S2 of 

 the source 5*1 5*2. 



