CH.I] 



MICROSCOPE AND ACCESSORIES 



33 



§ 58. The Size of the Field of the microscope as projected 

 into the field of vision of the normal human eye (z. e., the virtual 

 image) may be determined by the use of the camera lucida with the 

 drawing surface placed at the standard distance of 250 millimeters 

 (Ch. IV.) 



§ 59. Table showing the actual size in millimeters of the field of 

 a group of commonly used objectives and oculars. Compare with the 

 graphic representation in Fig. 42. See also § 57. 





Equivalent 



Focus and 



N. A. of 



Objective 



Diameter 

 of Field 

 in mm. 



Equivalent 

 Focus of 

 Ocular 



Kind of 

 Ocular 





_85 mm . 



15-4 

 10.6 



8-3 



37>£ mm. 

 25 



I2# " 



Huygenian 









45 mm. . 



7.0 

 4.0 



37^ mm. 



25 



12^ " 



Huygenian 





17 mm 



N. A. =0.25 



3-0 

 2.0 

 1.6 



37^ mm. 

 25 " 

 12^ "• 



Huygenian 





5-7 

 2.8 

 1.4 

 0.97 



180 mm. 

 45 



15 " 

 10 



Compensation 





5 mm. _ . 



N. A. =0.92 



o.54i 

 0.371 

 0.290 



37^ mm. 

 25 " 



I2# " 



Huygenian 





0.850 

 0.501 

 0.250 

 0.173 



180 mm. 



45 " 

 15 " 

 10 



Compensation 





2 mm 



N. A.=i.25 



0.270 

 0.186 

 0.147 



37^ mm. 

 25 



I2# " 



Huygenian 





' 0-45O 

 0.251 

 0.125 

 0.088 



180 mm. 

 45 

 15 

 10 



Compensation 



