Illuminating Apparatus. 
A. For white light. 
No. 
Marks 
17 
* 
Illuminating Apparatus after Abbe (new anangeinent). 
The essential feature of this is a condenser sj^steni of short 
focus, which collects the light reflected by the mirror into a cone 
of rays of very large aperture and projects it on the object. 
The full aperture of the illuminating cone should only be used 
when finely granular and deeply stained particles (bacteria) are being 
examined with objectives of large aperture. In every other case 
the cone must be reduced to suitable dimensions either by an iris 
diaphragm (see below) or common diaphragm (central illumination). 
On placing the diaphragm excentrically , by means of the rack 
work attached to the carrier, the central rays are excluded, and a 
certain extra-axial portion of the illuminating pencil falls upon the 
object (oblique light). When the diaphragm is thus excentrically 
placed this oblique pencil can be directed from all azimuths by 
rotating the carrier round the optic axis. 
The central stop diaphragm shuts off all the axial and trans- 
mits only the marginal rays (dark-ground illumination; see special 
instructions). 
