CH. XIV] EFFECT OF APERTURE IN PROJECTION 609 



This shows a heavy loss in light, the absorption being non- 

 selective, that is the total energy transmitted is in proportion to 

 the light. 



854. Example of light and energy losses. In fig. 342 is a 

 diagrammatic representation of the light and energy losses actually 

 found in a certain projection system. An arc light was used. 

 The light and energy from the arc striking the first surface of the 

 condenser were each called 100%. 



After passing the first part of the condenser LI, there remains 82% 

 of the light and 54% of the energy. 



After passing the condenser water-cell the light was reduced to 

 73% while there was left only 16% of the energy. 



After leaving the second part of the condenser L 2 , there was 68% 

 of the light and 14% of the energy. Of this remaining 14% of the 

 energy, 57% is invisible and 43% is visible as light. 



When used with a magic lantern the projection objective trans- 

 mits only 70% of the light reaching it. As 68% of the original 

 light reaches the objective, the screen image must be formed by 

 68 x 70 = 47.6% of the original light. 



With the microscope further losses occur due to the presence of 

 the stage water-cell. The microscope objective lets through but a 

 small amount of the light incident upon it, the loss being greater 

 the higher the power of the objective. A 16 mm. objective, for 

 example, transmits 10% of the incident light. In the case investi- 

 gated only 10 x 60 = 6% of the light originally striking the first 

 lens of the condenser reached the screen. If a substage condenser 

 and an ocular are used the light for the screen image is still further 

 reduced. 



EFFECT OF APERTURE 



855. Increasing the aperture of a perfect lens or a combina- 

 tion of lenses with undirected light has two effects. 



i. It increases the definition, that is, the image shows finer 

 structures than does a lens of smaller aperture, i. e., it will show 

 more lines to the millimeter or inch. See under Abbe diffraction 

 theory 910. 



