ELEMENTARY PHOTO-MICROGRAPHY. 25 



sacrifice of magnification. Great care, however, 

 must be exercised when not using the eyepiece, or 

 the reflection 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 

 microscope 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 eyepiece in position, remove the eyepiece, 

 and immediately a bright central spot of light will 

 appear on the paper. If the paper be now moved 

 to or from the end of the microscope, the bright 

 spot of light will gradually expand into a bright 

 ring of light, and then resolve itself into a point 

 again. The whole surface of the illuminated disc 

 is, of course, much more brilliant without the eye- 

 piece, reducing exposure considerably, yet the 

 defect in uniformity of illumination would 

 spoil the negative. On replacing the eyepiece 

 the brightspot of light vanishes, and the whole 

 disc is equally lighted, though not so brightly 

 as before. 



A tube of black velvet, plush surface inside, 

 made to slip into the body tube of microscope, 

 will be effective in preventing glare or flare spots 

 when no eyepiece is employed. 



