By the aid of the iris diaphragm the diameter of the aperture may be varied from approximately ⅗ to ⅛ of an inch.
The sub-stage, with condenser, iris diaphragm and mirror, 4.
An iris diaphragm regulates the intensity of incident light.
In the lower power objectives the angular aperture is to be reduced by the iris diaphragm.
To illustrate the functions of the iris diaphragm we will take the Williamson instrument.
Ground or colored glass discs may be inserted above the iris diaphragm if modification of the light is desired.
Ground glass and colored plates may be inserted above the iris diaphragm.
The condenser and iris diaphragm form one piece, giving central but no oblique illumination.
A ring below the iris diaphragm permits the insertion of glass discs for the purpose of modifying the light.
A round glassplate is set in the stage, below which is an iris diaphragm to properly regulate the illumination.