80 



PROGRESS IN MICROSCOPY 



that the phase plate remains geometrically identical, too. Were such 

 not the case, e.g. the objective's focal changed, the diaphragm ring 

 must also be changed. This is why, in many microscopes, the con- 

 denser carries, close to its focal plane, a revolving sub-stage comprising 

 rings of various sizes. A specific ring applies to every type of objective. 

 Leitz has perfected a phase-contrast microscope in which the annular 

 diaphragm of the condenser is substituted for a special condenser, 

 devised by Heine, whereby a mere adjustment makes it suitable for 

 any objective. Heine's condenser (denoted by M in Fig. 2.15) is sub- 



P ^^^^^.^^■.^■ 



\,'-^yA^V44 \'~-—\ 



(g) 



M 



Fig. 2.15. Heine's condenser (Leitz). 



stituted for the standard one and set under the specimen P. It consits 

 of the fixed lens L and the optical system C, sHding within the draw- 

 tube T. The paths of the light-rays from the optical system C are 

 shown in Figs. 2.16(a) and 2.16(b), The light-rays from the lens L (not 

 shown in Fig. 2.16) are first reflected by the plane portion hh and, 

 next, by the annular mirror del and emerge at ee (Fig. 2.16(a)). The 

 system C, consisting of a glass member, is shown by the dark area 

 in Fig. 2.16. Except in the central area x and the annular area ee, 

 the faces of the system C are made reflective by metallization. The 

 annular area replaces the usual condenser diaphragm. The micro- 

 scope's objective consists of the lenses Z^, 4, Aj and the phase-plate O. 

 In the position shown in Fig. 2.16(a), the system C is rather far from 

 the specimen, e.g. about 20 millimetres. This is why the lenses /i 

 and 4, the focal of which are short, can image the ring ee on the phase- 

 plate Q within the objective. 



