THE OPTICAL EQUIPMENT 



81 



bright and as white as possible. It is also necessary to have 

 one or two oculars of high power. 



It is probably understood that the value of an objective 



c d 



FIG. 8. Photographs of Abbe Test-plate. 



depends not on its magnifying power, but on its ability to 

 resolve fine details, and this is purely a function of its aperture. 

 In testing objectives for ordinary work, it is not only necessary 

 to determine the resolving power, but more especially to find 

 out the quality of the image, and the power which the objective 



