282 



HIGH POWER MICRO-PROJECTION 



[Cn. IX 



(2-3 mm. oil or water immersion) and for the 3 and 4 mm. dry 

 objectives the condenser is usually very close up to the slide, so 

 that the object is practically in the focus of the beam of light. 



For the 8, 10, 12, and 16 mm. objectives the substage condenser 

 must be separated sufficiently from the specimen to light the whole 

 field. 



It will be found in practice that one must be more precise in 

 keeping the substage condenser at just the right level for projec- 

 tion than for ordinary direct microscopic observation. Hence, it 

 will be found that for a thin slide the condenser, even for high 

 powers, may need to be separated slightly from the object, while if 

 the slide on which the specimen is mounted is thick, the condenser 

 may need to be as close to it as possible. 



408. Screen distance for high power projection. This 

 should not be excessive, for even in the darkest room the image will 



FIG. 157. LEWIS WRIGHT'S PROJECTION MICROSCOPE. 



(From Wright's Optical Projection). 

 C Condenser of three plano-convex lenses. 

 -1 Alum eell for absorbing radiant heat. 



P Plano-concave lens of highly dispersive glass to aid in correcting the 

 aberrations of the condenser and to render the light parallel. 



S C Substage condenser. For low powers but one lens is used. 



.V Stage. 



() Object and objective. 



A M Amplifier. 



F Fine focusing adjustment. 



R 2 Rack and pinion, coarse focusing adjustment. 



.ft, Coarse adjustment for the substage condenser. 



