172 



PHOTOMICEOGEAPHY 



A Ti/r -a ,. ( Exposure varies as (magnifi- 



4. Magnification { . . 9 



} cation) 2 . 



5. Condensing system.. . Amount of light utilised. 



J Air or oil between condenser, 

 \ objective, and slide, 

 j High eyepieces require a large- 

 \ ly increased exposure. 



6. Immersion medium . 



7. Eyepiece 



^t. fits density, contrasts, colour, 



o. Ubiect < ,. ,. 



(^ and mounting medium. 



9. Plate Speed and colour sensitiveness . 



Systematised Exposure. A worker who does not greatly 

 vary the conditions under which he makes his exposures 

 can give definite values to some of these factors, and 

 arrive at a fairly accurate exposure time by multiplying 

 them together, and then multiplying his unit of exposure 

 by the product ; the unit of exposure being the time 

 required under certain definite conditions. 



As an example some tables are appended, taken by 

 permission of Messrs. Wratten and Wainwright from 

 their booklet Photomicrography, referring to their "M" 

 panchromatic plates and " M " screens. Other plates 

 with different colour sensitiveness, and screens with 

 greater or less absorptions, will require different factors, 

 which can be determined by experiment. 



Effect of N.A. Exposure varies as ^ A : 



(JM.A.) 



