Ch. VII] 



PHOTOGRAPHING WTH THE MICROSCOPE 



231 



the specimen to be photographed must be of special excellence for 

 all powers. No one will doubt the truth of the statement who under- 

 takes to make photo-micrographs at a magnification of 500 to 2000 

 diameters. 



If one has a complete outfit with electric arc light the time required 

 for photographing objects is much reduced, i.e., ranging from 1 to 

 20 seconds even with the color screen. As the 

 light is so intense with the arc light it is neces- 

 sary to soften it greatly for focusing. Several 

 thicknesses of ground-glass placed between the 

 lamp and the microscope will answer. These are 

 removed before taking the negative. It is well 

 also to have a water bath on the optical bench 

 to absorb the radiant heat. This should be in 

 position constantly (see fig. in, 131). 



§ 357. Use of oculars in photo-micrography. 

 — There is much diversity of opinion whether 

 or not the ordinary oculars used for observation 

 should be used in photographing. Excellent re- 

 sults have been obtained with them and also 

 without them. 



When an ocular is used the eye-lens serves to 

 project a real image of the objective, not to act 

 as a magnifier with the eye as an ordinary obser- 

 vation ; therefore for the best results in photog- 

 raphy this eye-lens should be a combination 

 which will give a correct image. For apochromatic objectives only 

 the projection or the compensation oculars should be used, not or- 

 dinary Huygenian oculars. The projection and compensation oculars 

 work well with the best high-angled achromatic objectives also. 



Fig. 138. Ach- 

 romatic SUBSTAGE 

 Condenser for 

 Photo - microg - 



RAPHY. 



(From Watson's 

 Catalogue). 



1, 2, 3 The three 

 optical parts of the 

 condenser. (Com- 

 pare fig. 39 and 40, 

 also the construc- 

 tion of objectives in 

 fig. 21 A B C and 

 note that the con- 

 denser is like an in- 

 verted objective.) 



