nutting: brightness of optical images 



131 



APER- 

 TURE 



1 



2 



10 



•20 



oO 



100 



w = 



.704 



.1902 



.0312 



.00785 



.00196 



.000314 



.000878 



?n = .1 



. 580 



. 1580 



.0255 



.00()25 



.00102 



.000259 



.000065 



.521 



.1321 



,0219 



.00553 



.00134 



.000210 



.000051 



m = .5 



.333 



.0864 



.01290 



.00349 



.000878 



.000135 



.000044 



m = 1 



m = 2 



.179 



.4091 



.00785 



.00197 



.000490 



.000078 



.000019 



.0775 



.0210 



.00347 



.000870 



.000217 



.0000346 



.0000086 



J3Cf 



l_ 



I. 

 .0O3 



.s 



m 



10 



Fig. 2 



1.S 



Figure 1 shows relative brightness plotted against relative 

 apertures, both on logarithmic scales. The curves are sensibly 

 straight lines. 



Figure 2 shows the variation of relative brightness with rela- 

 tive distance of image and object, v/u. Relative brightness 

 decreases rapidl}^ at first, then slowly and steadily to zero for 

 great magnifications. 



In measuring relative illuminations the arrangement finally 

 adopted was that shown in figure 3. The test object was a sheet 



