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microscope is brought to its normal condition and the 

 projection of the image into the camera carries with 

 it the faults of the eye-pieces, and these increase with 

 the length of the camera. Without the use of the eye- 

 piece the spherical and chromatic correction of the 

 objectives is disturbed in proportion as the plate is 

 distant from the standard tube length and will destroy 

 the definition of a high power objective unless com- 

 pensation can be made by means of collar correction. 



The plan followed by a well-known worker is to 

 take a negative at the end of the tube without the 

 eye-piece, where the proper corrections are obtained, 

 and from this enlarge to any suitable size. 



The amplifier should be used where the eye-piece 

 is not employed, as by its proper adjustment the 

 objective may be brought to its normal condition. 

 This is the principle involved in the Rafter camera. 

 Its use is therefore not that of an amplifier but that 

 of a corrector. 



The question of suitable objectives is one of con- 

 considerable importance. The ordinary microscope 

 objective is not constructed with a view to photo- 

 graphic work, and unless nicely corrected there will 

 be a lack of coincidence between the visual and chem- 

 ical rays, /. e. between the image which is seen on the 

 ground glass and that which is photographically pro- 

 duced. For all this, practical experience has shown 

 that a number of Bausch & Lomb Optical Co. objec- 

 tives are well suited to this work. For low powers 

 the Student and Professional series may be success- 



