Microscopes use light and lenses to magnify objects. Magnification is when small objects are made to look larger in order to see fine details. When oil is used to fill the gap between the object being viewed and the lens, an even greater magnification is possible. The process of using oil to increase magnification is called oil immersion.
Using a microscope:
Once an object is placed on the microscope and is ready to be viewed, look through the eyepiece.
While looking through the eyepiece, adjust the focus knob on the microscope to bring the object into focus.
To adjust the amount of light entering the microscope, the iris/diaphragm can be used. The diaphragm regulates the amount of light that is released towards the specimen.
To increase magnification, many light microscopes have different lenses that can be rotated into place.