PHYSICAL ASPECTS OF IMAGE FORMATION 



53 



test is the same as before: resolving power is reached when the drop 

 in intensity between the two images amounts to 26 per cent. If the 

 condenser is ahnost fully diaphragmed, illumination is coherent and 

 formula (1.11) applicable. The coefficient K, by which A/(2/7sinM) is 



Fig. 1.69. Aspect of an object consisting of luminous points on black ground: incoherent 



illumination. 



to be multiplied in order to have resolving power y, is plotted in 

 Fig. 1.71, as ordinate and the ratio m as abscissae 



m 



Condenser N.A. 

 Objective N.A. 



When w=0 (coherent illumination), ^=1-63 (expression 1.11). 

 When m = 1, i.e. when the N.A. of both condenser and objective 

 is the same (partially coherent illumination), K = 1 22. Separation 



