The light microscope is a scientific optical instrument, which is used to study microscopic living and prepared specimens. It is also employed to study specimens with inherent fluorescent properties. It has a built-in light source and an adjustable sub-stage condenser, which projects light into the objectives. A mechanically-operated stage carries the specimen. Meanwhile, the objective magnifies the specimen image and the oculars complete the image-formation process.
Image Formation
A modern light microscope has a resolution limit of 0.2 to 0.4 μm, or approximately one twentieth the diameter of the human erythrocyte (red blood cell). Thus, not only is it used to study living cells but also most of their organelles, because they fall within this size range. When specimens are carefully prepared, these organelles are visible in the light microscope, except for ribosome, which was discovered with an electronic microscope.
The resolving power of a light microscope depends on three variable; objective magnification; objective numerical aperture; and the wavelength of light used to illuminate the specimen. A typical compound light microscope has a low-power (4x) objective, one intermediate power (10x, 40x) objective, and one high-power (100x) oil immersion objective.
Below, a Carl Weiss light microscope, with their components being labeled
