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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
§ HO?)
§ 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 position of any part or parts is, of co.urse, 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 objective 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 necessary aperture of the lighting beam, and to use an ocular to compensate for objective defects. If one uses a water or an oil immersion 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 substage condenser used for ordinary observation is designed for ap