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CHAPTER VI 

 MEDIUM-POWER PHOTO-MICROGRAPHY 



The term medium power photo-micrography is usually restricted to magni- 

 fications extending to about five or six hundred diameters, where it is necessary 

 only to use an inch or a half-inch objective, and in some cases a sixth. Critical work 

 is said to commence where medium leaves off, and is so called because all adjust- 

 ments, centreing and focussing, are of the highest order possible. For this purpose 

 too the highest N.A. is always necessary such as is obtained by the use of an ^ or iVth. 

 The use of a sixth objective may be said to lie on the border land between these two 

 divisions, but for convenience of description will be spoken of under critical or high- 

 power work. 



In this chapter, Section I, treats of the following : — 



(i) The different methods of illuminating an object placed on the microscope. 



(ii) To explain how to ascertain the amount of magnification given to any 

 specimen photographed. 



(iii) To give details of an arrangement to exclude all extraneous light entering 

 the camera at its point of juncture with the microscope. 



(iv) How the microscope may be firmly fixed on to the baseboard of the 

 apparatus. 



Section II. is devoted to explaining the actual method of taking the photograph. 



(i) By ordinary transmitted or direct light, using an inch and a half objective, 

 with remarks upon the special development which may be required, thinning and 

 intensifying the negative ; and also some remarks concerning different arrangements 

 of lenses, camera length and eye pieces for obtaining the same magnification. 



(ii.) By the other various forms of illumination — reflected light, oblique light, dark 

 ground illumination, and the treatment of opaque objects, and with polarised light. 



