How Does a Light Microscope Work?

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A light microscope uses a focused beam of visible light to magnify objects for observation. It works in a similar way as a refracting telescope but with several minor differences. A telescope uses a large objective lens, because it needs large amounts of light to bring a dim, distant object to a bright focus. On the other hand, a light microscope does not need a large objective lens because it only needs to acquire light from a small area of a thin, close specimen that is well illuminated.

A light microscope uses a tiny and spherical objective lens, and it has a shorter focal length on both sides. A microscope brings an object’s image into focus at a close distance within the tube. A second lens, called the eyepiece or ocular lens, magnifies the image. Aside from a light source, a microscope also has a condenser, which focuses light from the source to a small, bright spot of the specimen.

Compared to a telescope, which has interchangeable eyepieces and a fixed objective lens, a microscope has fixed eyepieces and interchangeable objective lenses. It can magnify incredibly small areas when the objective lenses are changed from flat, low-magnification lenses to rounder, high-magnification ones. The image quality seen using a light microscope is assessed based on brightness, resolution and contrast. Light microscopes are typically used to examine cells and organelles.