Compound microscope is an optical device used to obtain very large values of magnification. It is used to see microscopic objects like microorganisms. It comprises of two convex lenses and magnification occurs in both of them. Its basic components are:
1. Objective: Convex lens placed near the object. Object is placed just beyond the focal point. Image formed in real, inverted and magnified. 2. Fine adjustment screw: This is used to adjust the position of objective lens. A small movement in this causes a lot of change in magnification. 3. Eyepiece: Convex lens placed near the eye. It forms a virtual object of the real image formed by the objective lens. Hence, its position is designed such that image from the objective falls between its focus and centre. 4. Rough adjustment screw: This is used to form a clear image and focus at the correct part of the object to be seen. Working Principle: Light from a light source (mirror or electric lamp) passes through a thin transparent object. The objective lens produces a magnified real image first image) of the object. This image is again magnified by the ocular lens (eyepiece) to obtain a magnified virtual image (final image), which can be seen by eye through the eyepiece. As light passes directly from the source to the eye through the two lenses, the field of vision is brightly illuminated.