384 PHOTOGRAPHY AND PROJECTION [Cn. X 



545. Objectives to use. The microplanars (fig. 123) or 

 other short focus objectives of the photographic type are used 

 without an ocular. They can be screwed into the nose-piece of the 

 microscope or the microscope can be dispensed with and the 

 objectives put into the end of the camera as with photographic 

 objectives. 



If one wishes to use the ordinary microscope objectives then an 

 ocular of the projection type is of great advantage although 

 Huygenian oculars will give good results. The apochromatic 

 objectives, and the projection or compensation oculars to go with 

 them, give the best results. 



546. Making the negative. The image is first focused very 

 sharply on the focusing screen. For lights of high intensity it will 

 be necessary to soften the light in focusing so as not to injure the 

 eyes. This can be done by putting a neutral tint glass plate or 

 several thicknesses of ground -glass or one or more plates of milky 

 glass in the path of the beam before the object. 



The exposure and subsequent development and printing with the 

 negative are as usual. 



547. Photo-micrography with a vertical camera. If a ver- 

 tical microscope is to be employed for photography, then it is best 

 to use a vertical camera (fig. 217). A parallel beam of light is 

 caused to fall upon the plane surface of the microscope mirror, and 

 the mirror is turned to throw it directly up through the substage 

 condenser upon the object. To get the parallel or approximately 

 parallel beam one uses a condenser lens of very long focus ( 479, 

 fig. 154) or a parallelizing lens is used (fig. 153). 



TROUBLES MET IN CHAPTER X 



548. The troubles liable to arise in the work of this chapter 

 are those common to the preceding chapters. Those discussed in 

 Chapter I and III are to be especially reviewed, as the source of 

 light is most likely to be the electric arc. (See i28a for the 

 blowing of fuses). 



(i) In drawing with the microscope with the small carbon arc 

 lamp on the house lighting system, probably the trouble most 



