CH. VII] PHOTOGRAPHING WITH THE MICROSCOPE 



227 



137), use that for making the negative as follows: Swing the camera 

 around so that it will leave the microscope free (fig. 129). Use an 

 ordinary ocular, focus and light the object, then insert a projection 

 ocular in place of the ordinary one, and swing the camera back over 

 the microscope. It is not necessary to use an ordinary ocular for the 

 first focusing, but as its field is larger it is easier to find the part of 

 be photographed. The first step is then 

 to focus the diaphragm to the projection 

 ocular sharply on the focusing screen. 

 Bring the camera up close to the micro- 

 scope and then screw out the eye-lens 

 of the ocular a short distance. Observe 

 the circle of light on the focusing screen 

 to see if its edges are perfectly sharp. If 

 not, continue to screw out the eye-lens 

 until it is. If it cannot be made sharp 

 by screwing it out, reverse the opera- 

 tion. Unless the edge of the light circle, 

 i. e., the diaphragm of the ocular, is 

 sharp, the resulting picture will not be 

 satisfactory. 



It should be stated that for the X2 

 projection ocular the bellows of the cam- 

 era must be extended about 30 or 40 

 centimeters or the diaphragm cannot be 



satisfactorily focused on the screen. The X4 projection ocular can 

 be focused with the bellows much shorter. For either projection 

 ocular the screen distance can be extended almost indefinitely. 



When the diaphragm is sharply focused on the screen, the micro- 

 scope is focused, that is, first with the unaided eye then with the fo- 

 cusing glass. The exposure is made in the same way, as though no 

 ocular were used ( 3490), although one must have regard to the greater 

 magnification produced by the projection ocular and increase the time 

 accordingly; thus when the X4 ocular is used, the time should be at 

 least doubled over that when no ocular is employed. The time will 

 be still further increased if a color screen is used ( 376). 



Draw- 

 Tube 



FIG. 134. LIGHT EXCLUDER 

 FOR PHOTO-MICROGRAPHY. 



(About j natural size). 



In this figure the different 

 parts of the light excluder are 

 in position for making an ex- 

 posure. 



1 The front board of the 

 camera. 



2 The intermediate part 

 connecting the camera and 

 the hollow cylinder on the 

 upper end of the microscope 

 draw-tube. (Compare fig. 



