3o6 MAGNIFICATION OF OBJECTIVES AND OCULARS [Ch. IX 



scope or it is like that of a projection microscope when the objective 

 alone is used (fig. i8i, 182). As pointed out in § 236 it is necessary 

 to select some standard distance for the projection of the real or of 



Fig. 182. Projected Virttjal Image of a Magnifiee. 

 (Simple Microscope or Ocular). 



The projection distance is 250 mm. from the nodal point in the crystalline lens 

 of the eye. 



Axis The optic axis of the magnifier and of the eye. 



A^ £' The object of the simple microscope or real image of the objective. 



B' A' The retinal image (inverted). 



A^ B' The projected virtual image. It is erect as compared with the object, 

 but inverted as compared with the retinal image. 



Cr. Cornea of the eye. 



R Single refractive surface of the schematic eye. 



L Crystalline lens of the eye. 



the virtual image, for the size of the image varies directly as its dis- 

 tance from the center of the lens (fig. 181 for real and 182 for virtual 

 images; in the latter the projection distance is from the nodal point 

 in the eye to the image). The image distance for magnification most 

 commonly employed is 250 mm. (§ 236). 



