8 



MICROSCOPE AND ACCESSORIES 



\_CH. I 



1 i ) That every convex or converging lens or lens system can 

 serve to form either a virtual or a real image, depending upon its 

 position with reference to the object. 



(2) They show also that without changing the position of the 

 magnifier, if it is slightly further from the object than its principal 

 focal distance, either a virtual image or a real image may be seen by 

 many people, depending upon the position of the eye. (a) If the 

 eye is close to the magnifier an enlarged erect virtual image will be 

 seen. (b) With the eye at a considerable distance an enlarged 

 inverted real image may be seen. 



Fig. 1 6 B. Figure to show that with a 

 simple microscope if the object is slightly be- 

 yond Ihe principal focus -(F) a real image 

 will be formed at A' which can be seen by an 

 eye at , and that if a normal or hyperopic 

 eye is at E f a virtual image can be seen 

 without changing the position of the simple 

 microscope. The long-sighted eye can see 

 this image best as it naturally focuses con- 

 verging rays on the retina. The myopic eye 

 either sees no image at all, or a mere blur, 

 depending .upon the amount of myopia. A. 

 object; A/ real image above the magnifier ; 

 A." virtual image which can be seen below 

 the lens by an eye at E> '; E. eye in posi- 

 tion to see a real image ; E. f eye in position 

 to see A" a virtual image; F. principal 

 focus of the magnifier. 



FIG. 17. Tripod Magnifier. 



While the law is absolute that real images are formed only when 

 the object is without the principal focal distance, and virtual images 

 only when the object is within the focus, the above experiments show 



