CHAPTER V 



OBJECT GLASSES AND EYEPIECES 



Scratches 

 and dirt 

 on object 



Dirt on 

 eyepieces. 



Gleaning 



The object glasses and eyepieces are of such paramount impor- 

 tance in the performance of a microscope that their use and 

 selection is a matter which should receive the careful consideration 

 of the microscopist. Each object glass is a complicated combina- 

 tion of lenses and metal parts. In some as many as ten, and in 

 none less than four, lenses, mounted in their cells at specified 

 distances apart, form the complete whole. The adjustment 

 and setting of these demands the utmost skill and care in 

 manufacture ; an error of 1/10000 of an inch may damage the 

 quality of a high-power lens. 



Scratches upon the. surf aces of the lens, or dust either on or 

 between the components, unless in an aggravated form, do not 

 interfere with its performance beyond stopping or scattering a 

 little light, but the slightest shifting of one of the lenses or the 

 least smear of grease or moisture wUl entirely upset the corrections 

 and ruin its performance. No glass surface should ever be touched 

 by the fingers, as they always leave a smear of grease. It is, 

 therefore, of the utmost importance to treat all object glasses, 

 eyepieces, and condensers with care, and to keep them free from 

 moisture, dirt, or grease. They wiQ, even with the greatest care, 

 collect dust from the atmosphere in time, but they should always 

 be kept in a dry place, especiaEy when in a moist cUmate. 



Dirt in the eyepieces shows in the field of view, that on the 

 object glasses is not clearly visible, but may make the image 

 hazy and indistinct. It is quite readily detected in the eyepieces, 

 as by revolving the eyepiece in the diawtube the specks due to 

 dirt in the eyepiece will revolve. If the specks are on the object 

 or in the observer's eye, they will remain stationary. 



To remove dirt from the eyepiece, the surfaces should be 

 carefully cleaned with a very soft piece of well- washed silk ; and 

 if after this any still adheres, the silk should be moistened with a 

 little xylol or alcohol. For this purpose it is quite safe for the 

 microscopist to imscrew the cells, which hold the lenses, from 

 the eyepiece tube, provided that care is taken to replace them at 

 the right ends. It is best to only unscrew one at a time. It is 

 inadvisable for the microscopist to attempt to. clean the internal 

 lens surfaces of an object glass ; the interior surfaces do not readily 



76 



