PROJECTION MICROSCOPY 



Unocutar 



« -ray scfean 



spedmenheUer 



concave mirror 



correction lens 



plane mirror 



focusing screen 



electron gun 



lODrnm 



Fig. 8. Simplified cross section of the microscope shown in Fig. 7. 



rupt the electron beam. The image field is 

 about 25 mm on the fihn. (Angular field 

 approx. 36°.) 



The anode voltage is variable in four steps 

 from 5 to 20 kV. In each position the lens 

 current is automatically adjusted so that 

 the lenses maintain the same strength. 



The desk model housing contains the me- 

 chanical and diffusion pumps, the high volt- 

 age and lens current supply, and the elec- 

 tronic stabilizer. 



Practical X-ray Microscopy 



In general, the brightness of the fluores- 

 cence images is so low that they are not suit- 



able for visual observation. Another conse- 

 quence of this low intensity is the poor 

 contrast. As the visibility of a detail will be 

 limited by quantum noise, a considerable 

 gain cannot be expected from an image inten- 

 sifier unless it has a large storage time, pref- 

 erably with a contrast correction. Admit- 

 tedly, such a device would bring the screen 

 brightness to a convenient level, eye adapta- 

 tion not being necessary, but an image 

 intensifier is a much too complicated instru- 

 ment to use it for this purpose only. The use 

 of fluorescent screens with better resolution 

 in combination with a high-aperture micro- 

 scope objective may do the same. 



667 



