CH. X] 



DO AND DO NOT IN DRAWING 



389 



6. In drawing with any form 

 of projection apparatus the 

 axial ray must strike the draw- 

 ing surface at right angles or 

 the image will be distorted 

 (483)- 



7. Make sure that the mirror 

 or prism reflects the rays upon 

 the drawing surface so that the 

 axial ray is at right angles to 

 the surface (482-483). 



8. Use a condenser of suffi- 

 cient diameter to fully light the 

 object ( 467, 533). 



9. Get the desired size for the 

 drawing by making the distance 

 of the drawing surface greater 

 or less, or by using a different 

 optical system for the projec- 

 tion (465, 507-508). 



10. Take great pains to light 

 as brilliantly as possible ( 497, 

 and Chapters I, II, and IX). 



11. Take care to have the 

 images on the drawing surface 

 erect ( 512-526). 



12. In using projection ap- 

 paratus for photography, re- 

 member the principles of good 

 projection, and the require- 

 ments for good photography. 



6. Do not draw distorted 

 pictures; therefore do not have 

 the axial ray strike the drawing 

 surface obliquely. 



7. Do not forget to incline 

 the mirror used in drawing so 

 that the axial ray will strike the 

 drawing surface at right angles. 



8. Do not try to project an 

 object larger than the diameter 

 of the condenser lenses used. 



9. Do not neglect to give the 

 scale at which every drawing is 

 made. 



10. Do not expect good light 

 unless the conditions for it are 

 met. 



11. Do not draw inverted 

 images. 



12. Do not expect projection 

 apparatus to give good photo- 

 graphs unless sharp, brilliant 

 images are projected, and 

 the photographic part is done 

 correctly. 



