14 ELEMENTARY PHOTO-MICROGRAPHY. 



and lighting from one position. A trifle longer 

 exposure is of no moment to a beginner, since the 

 time lost in this way is saved in the facilities offered 

 for focussing. The errors of objectives also are 

 corrected by eyepieces, and good results can be ob- 

 tained when using them for photographic as for 

 visual purposes. The C eyepiece, although giving 

 great power of enlargement, is not recommended 

 when a lower power will do. Yet the writer has 

 been able to get capital results with C eyepiece 

 when the same magnification had been obtained by 

 a low eyepiece and a high objective with less 

 success. 



But clearness of definition must never be sacrificed 

 for the sake of a larger picture. A crisp negative 

 may be enlarged, whilst a larger image wanting in 

 sharpness is valueless. The only advantage 4*> be 

 gained by a C eyepiece is that it allows a low-power 

 objective to be used with greater depth of focus. For 

 dark ground illumination and for polariscope work 

 the eyepiece may be dispensed with at the sacrifice 

 of magnification. Great care, however, must be 

 exercised when not using the eyepiece, or the reflec- 

 tion from the interior of the body tube will manifest 

 itself in the form of a bright central spot on the 

 negative. 



The use of an eyepiece removes this entirely, but 

 by way of object lesson let the reader take a micro- 

 scope that is not dead blacked inside the tube, and 

 throw the image of an object on to a sheet of 

 paper. After getting even illumination with the 



