Answer: it controls the amount of illumination used to view the object , It has different sized holes and is used to vary the intensity and size of the.
Detail:
Diaphragm: Diaphragm helps in controlling the amount of light that is passing through the opening of the stage. It is helpful in the adjustment of the control of light that enters.
Iris Diaphragm controls the amount of light reaching the specimen. It is located above the condenser and below the stage. Most high quality microscopes include an Abbe condenser with an iris diaphragm. Combined, they control both the focus and quantity of light applied to the specimen.
Diaphragm or Iris: Many microscopes have a rotating disk under the stage. This diaphragm has different sized holes and is used to vary the intensity and size of the cone of light that is projected upward into the slide. There is no set rule regarding which setting to use for a particular power. Rather, the setting is a function of the transparency of the specimen, the degree of contrast you desire and the particular objective lens in use.
Diaphragm – often called aperture – is part of beam or image control system. It’s aim is to improve beam shape (in condenser system) or image contrast (in objective system).
Physically diaphragm is a metal or plastic strip with number of holes in it – each hole have a specific diameter.
In condenser (beam) system size of the diaphragm sets the illumination intensity and convergence angle.
In objective (image) system the diaphragm “screens” parts of the beam that are not needed for this specific image and this way improves the image contrast.
