ing powers and in combination give the greatest 

 magnification admissible with single lenses. 



Doublet Magnifier. This lens, Fig. 16, recently 

 introduced, is composed of two 'separated plane convex 



lenses and, while not so 

 compact for pocket use, 

 eliminates some of the 

 optical defects of the 

 ordinary magnifiers. 



Fig. 16. 



Coddington Lens. A lens of greater efficiency 

 than either the ordinary magnifier or the doublet 

 magnifier is the Coddington lens, Fig. 17'. 



While this is also a single double convex lens 

 it, will be noticed that it has considerable thickness, 

 being really the central portion of a sphere and 

 provided with a circular incision at the middle, which 

 is blackened and thus 

 acts as a diaphragm, 

 shutting out the marginal 

 rays and correcting the 

 spherical aberration, at 

 the same time, however, 

 limiting the size of field. 



In selecting a Coddington, one should avoid those 

 which are of ten 'offered as the real and which consist 



