CH. VII I. .] 



/WO TO MICROGRAPHY. 



199 



necessary to focus down considerably to make the image clear. 

 Lengthen or shorten the bellows to make the image of the desired size, 

 then focus with the utmost care. In case the field is too much 

 restricted on account of the tube of the microscope, remove the draw 

 tube. When all is in readiness it is well to wait for three to five 

 minutes and then to see if the image is still sharply focused. If it has 

 got out of focus simply by standing, a sharp picture could not be ob- 

 tained. If it does not remain in focus, something is faulty. When the 

 image remains sharp after focusing make the exposure. From 15 to 

 60 seconds will usually be sufficient time with instantaneous plates and 

 the light as described. 



Fig. 156. Lens holder composed 0/ several links and balls, thus giving the flexi- 

 bility of a chain and enabling one to turn the lens in any desired direction. Each 

 link has a screw to take up wear, thus insuring permanence. The lens is grasped 

 by two movable pieces which open -widely enough to take a tripod or an engraving 

 glass ; they also hold ?vilh equal facility a -very much smaller lens. This is one of 

 the most efficient and satisfactory lens holders ever made. It is epecially good for 

 holding a lens for concentrating the light on the mirror in artificial lighting 

 (From the Bausch & Lomb Optical Co.) 



(B) Photographing until a Projection Ocular. — If the object is small 

 enough to be included in the field of a projection ocular, one may put 

 that in place of the ordinary ocular. The first step is then to focus the 

 diaphragm of the projection ocular sharply on the focusing screen. 

 Bring the camera up close to the microscope 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, con- 

 tinue to screw out the eye-lens until it is. If it cannot be made sharp 

 by screwing it out reverse the operation. Unless the edges of the light 



