CH. X] DRAWING WITH PROJECTION MICROSCOPE 335 



474. Varying the drawing distance. The drawing distance 

 is easily .varied by means of a movable table like that figured (fig. 

 182), or by an adjustable shelf attached to the projection table (fig. 



183)- 



Another way of varying the size of the drawing is to use higher or 

 lower objectives, the drawing distance remaining the same (see 

 57)- 



475. Lighting the object. For large objects and low powers 

 the best way to illuminate the object is to use the main condenser 

 only and to put the object in the cone of light where it is fully 

 illuminated (fig. 132). If the drawing shelf is used this will involve 

 moving the lamp and condenser toward the drawing-board ; for the 

 microscope must be beyond the end of the table, so that the image 

 can be thrown down on the shelf, (fig. 186). The change in posi- 

 tion of any part or parts is, of course, very easy with an optical 

 bench (fig. 158-159). 



476. Drawings with objectives of 16, 12, 10, and 8 mm. 



With objectives of this range without an ocular, one can draw 

 objects varying from 5 to 2 mm. in diameter. For lighting, use the 

 large condenser and focus the image of the crater on the hood of the 

 objective (fig. 140), and then push the stage up toward the objec- 

 tive until the object is in focus, finishing the fine focusing with the 

 micrometer screw of the microscope. 



DRAWING WITH THE PROJECTION MICROSCOPE, INCLUDING AN 

 OCULAR AND A SUBSTAGE CONDENSER. 



477. Drawing fine details with high powers (8 to 2 mm. focus) . 



As pointed out for the projection of images showing fine details 

 ( 401), it is necessary to use a substage condenser to get the neces- 

 sary aperture of the lighting beam, and to use an ocular to com- 

 pensate for objective defects. If one uses a water or an oil immer- 

 sion objective the proper immersion fluid must be used between the 

 cover-glass and the objective, as in ordinary microscopic work. 



478. Parallelizing the converging beam of light. The sub- 

 stage condenser used for ordinary observation is designed for ap- 



