4 
FIG. 2— EFFECT OF DIVERGENT RAYS 
ENTERING THE CONDENSER. 
The rays come to a focus below the object and 
the illumination is reduced. 
The rays are brought to a focus in the plane 
where the object lies. 
3. The Abbe condenser, H, receives the light falling on an area of the mir¬ 
ror equal in size to the lower lens of the condenser, and concentrates it on a 
much smaller area. (See Figs. 2 and 3). This increases the illumination and 
brilliance of the object, a result which is very important in the operation of 
high power objectives. 
4. The iris diaphragm, I, provides a means by which the amount of light 
entering the front lens of the objective may be regulated. It is especially of 
value when using the low power objectives because with them the definition 
and detail of the object is brought out more clearly when the light is not too 
intense. 
5. The oil-immersion objective gives the highest magnification. The front 
lens is very small and hence admits but little light. In order that the objects 
FIG. 4-SHOWING THE PRINCIPLE OF THE IMMERSION OBJECTIVE 
