DIAPHRAGM. 



53 



condenser. The mechanical stage should be tapped 

 for three (removable) screw studs to be used in place 

 of the sliding bar, so that if desired the Vernier finder 



FIG. 45. Mechanical stage. 



(Fig. 45, BE'), such as is usually fitted to this class of 

 stage, or a Maltwood finder, may be employed. 



6. Diaphragm. Separate single diaphragms must 



FlG. 46. Iris diaphragm. 



be avoided; a revolving plate pierced with different 

 sized apertures and secured below the stage is prefer- 

 able, but undoubtedly the best form is the "iris" 



