346 



COMPOUND AND ELECTRON MICROSCOPES 



This image position is comparable to the position of the magnified 

 real image found in the image plane of the optical microscope. In the 

 optical microscope, the real image is projected with the aid of a lens on 





w 6 



First image 

 plane 



Projection 

 coil 



/ i \ 



I \ 



I \ 



1 I ^ 



/ \ 



/ \ 



/ I 



I 



Ttf° 

 n\ 



'I 

 ' i l 



' ■*■ 

 / \ 



/ \ 



A. 



/!\ 



I 



E 



J- 



I 

 L 



I 



\ 



X 



Second image plane 



Vacuum 

 pump 



Fig. VIII-23. Diagrammatic section of a typical electron microscope projector 

 with hot cathode. The operation is analogous to the conventional light microscope 

 at right. Suitably shaped magnetic fields take the place of the glass lenses. Con- 

 denser lens C, objective lens system O, projection lenses E with final image in second 

 image plane. In the electron microscope the electrons leave the filament, are accele- 

 rated between G and F by about 50 kv, are converged by the condenser lens on the 

 specimen at S. After passing through the specimen, the objective lens coil forms a 

 first image at /, enlarged about 100 fold. The projection lens coil again magnifies 

 this image about 100 fold making an overall magnification of 10,000. Image can be 

 photographed at P. P2 is a port for viewing the fluorescent image, when a movable 

 fluorescent screen is placed in plane of image at P. 



the photographic plate of a camera attached to the barrel of the instru- 

 ment. In the same way the projection coil of the electron microscope 

 allows that section of the electron image covering its stop to be used for 



