72 ELEMENTARY PHOTO-MICROGRAPHY. 



a ioin. tube is the standard, and a negative taken 

 loin, away from the eyepiece will give an enlarge- 

 ment equal to that seen by the eye when looking 

 through the eyepiece. If the camera be now halved 

 in length the magnification is halved, and if the 

 camera be doubled the increase is in proportion. 



A table showing the enlargement due to the 

 various eyepieces and objectives is given by most 

 makers in their catalogues, and may be referred to 

 for ready reference. The same magnification may 

 be obtained by using a low power with the C eye- 

 piece, or a higher power with the A eyepiece, and 

 by altering the camera extension in each case. The 

 photographer must judge which method is best for 

 his purpose, remembering always that a low power 

 objective will give more depth of focus than a high 

 power, and the A eyepiece gives a brighter image 

 than the C eyepiece, consequently shortening the 

 time of exposure. 



The list is taken from the catalogues of various 

 makers, and is not based on any scientific system 

 of uniformity. No reliable nomenclature of eye- 

 pieces and objectives has yet been adopted for the 

 compilation of consistent tables. 



See definition of " Power " in glossary for fuller 

 information. 



The unit for microscopical measurement is the 

 micron (written n), the thousandth part of a milli- 



