Compound microscope. Objective. To learn about the construction and working of a compound microscope. A compound microscope has multiple lenses which collect light from the object and then focus the light into the eye. These microscopes have the ability to magnify very minute objects to a substantial size, clearly showing the smallest details. There are three major parts to the compound microscope. A body tube. An objective lens. And an eyepiece. The body tube is comprised of two smaller telescoping tubes with lenses coaxially mounted at either end. The wider tube holds the objective lens while the narrow tube holds the eyepiece. The knobs for both cores and fine adjustment allow the tubes to slide one into another, varying the distance between the two lenses. The lenses are convex with different focal lengths. The lens closer to the object is the objective and has a short focal length, F O, usually below 1 cm. The lens nearer the eye is the eyepiece. Although the eyepiece also has a short focal length, F E. It is still greater than the focal length of the objective. A revolving nose piece known as a turret is attached to the lower end of the objective. The turret can be rotated to change the power magnification as necessary. Below the objective sits a flat platform known as the stage. On the surface of the stage, two stage clips hold the slide in place. A small aperture is present in the stage, allowing light into the body. The body tube is arranged on an arm which is connected to a strong base. This arm allows the body of the microscope to tilt. A small mirror at the base of the microscope reflects the light through the stage aperture. Above the mirror, an iris, also known as a diaphragm is present. Iris helps in controlling the amount of light passing into the stage aperture. Working of the compound microscope. The object O is placed just outside F O, the focus of the objective lens. A rail inverted and magnified image I1 is formed. The magnified image I1 acts as an object for the eye lens. The eyepiece is adjusted such that the image I1 lies within the focus of the eyepiece F E. The eyepiece functions as a magnifying glass and forms a virtual erect and magnified image I2 of the object. Magnification of the compound microscope. The magnifying power of the lens is expressed in diameters. A lens magnifying an object 5 times has a magnification of 5 diameters and is written as 5x. The total magnification of a compound microscope is the product of the magnifying power of the objective and the magnifying power of the eyepiece. For example, if the objective has a magnification of 40x and that of the eyepiece is 10x. Then the magnifying power of the microscope is 400x. Summary. The compound microscope has a system of convex lenses allowing the magnification of minute objects to that of a very large image.