SUBSTAGE CONDENSERS 



107 



Substage Condensers. Substage Condensers are usually 

 combinations of two or more lenses, somewhat similar in 

 construction to objectives, but made to concentrate light 

 upon the object through the thickness of a slide. 



Chromatic Condensers The Spectacle Lens. The sim- 

 plest substage condensers are double convex lenses, such 

 as the " Spectacle " lenses of Zeiss, and are very suitable 

 for use with the small photographic lenses of 2" or 3" focus. 

 Occasionally an even larger lens than these about 2" 

 in diameter is useful to illuminate very large prepara- 

 tions. 



Abbe Condenser. The chromatic condenser of Abbe 



Fig. 33 



ABBE CONDENSER 



still maintains its position as the most frequently used 

 substage illuminating apparatus, and as made by firms of 

 repute it is a very efficient condenser, although far from 

 aplanatic its aplanatic cone is at the most 0-65 and 

 only corrected for one colour. It is supplied in two forms, 

 one with two lenses and a N.A. of 1-0 to 1-2, and the other 

 with three lenses and a N.A. of 1-3 to 1-4 (Fig. 33). The 

 latter should be oiled to the slide when used with oil- 

 immersion objectives ; and with its top lens removed 

 has a focal length of about J", or f ", forming a suitable 

 illuminator for low-power objectives. 



This type of condenser is fitted to most microscopes, 

 as more accurate corrections than those it embodies 

 are unnecessary for many purposes, but the superiority 



