l84 DRAWING WITH A PROJECTION MICROSCOPE [Ch. VI 



the photographic objective should be of rather long focus and thus 

 make it possible to have the camera at a considerable distance from 

 the object; then there will be avoided the exaggerated perspective 

 which comes from using a short focus objective. 



All the different objects or parts of a large object at different levels 

 will be in focus with the long focus objective at a considerable distance. 

 In projection it is very easy to make the picture as large as desired 

 provided the projection apparatus or the drawing surface is movable. 

 The projection method has the advantage of being applicable to all 

 forms of objects, gross and microscopic. The only precaution is to 

 make the negative rather thin, not dense; then the details come out 

 clearly in the projected image. 



Projection Microscope for Drawing 



§ 293. This is the most satisfactory method of drawing small 

 objects. With it one can draw large diagrams or small figures 

 directly from the objects; and if the apparatus is properly con- 

 structed one may make diagrams from objects 60 to 70 mm. in di- 

 ameter down to those of half a mUlimeter or less. This method was 

 much in vogue and highly commended by the older microscopists 

 who used the solar microscope (Baker, Adams, and Goring). Since 

 the general introduction of electric lighting, drawing with the pro- 

 jection microscope has become once more common and is the most 

 satisfactory method known, especially for the numerous drawings 

 necessary for the preparation of models in wax or blotting paper. 



§ 294. Drawings with low powers. — For objectives of 30 to 100 

 mm. focus the best method is to use a projection outfit with a three 

 lens condenser as shown in fig. iii. The whole should be on an 

 optical bench so that each element and all together can be moved at 

 will (fig. 131). 



For a radiant a large or a small arc lamp is best (fig. 49, 111-112), 

 but a 250 or 400 watt concentrated filament, stereopticon mazda 

 lamp filled with nitrogen also works fairly well. It has the ad- 

 vantage that it can be attached to any lighting circuit, and when 

 once centered and properly arranged requires no attention except to 



