Optical microscope

An instrument that uses visible light and lenses to magnify objects too small to see clearly with the unaided eye. Its resolving power is limited by the wavelength of light and the optical system.

Objective lens: The lens nearest the specimen that collects light and forms the microscope’s primary image. Its numerical aperture and magnification set much of the microscope’s resolving power.
Bright-field microscopy: A microscopy method that forms contrast mainly from light transmitted through a specimen against a bright background. It is the standard starting method for viewing stained or naturally absorbing samples.
Magnification: The ratio between an image’s apparent or measured size and the corresponding object’s size. Total microscope magnification combines the magnifying effects of its objective and eyepiece.
Electron microscope: An instrument that uses a beam of electrons and electromagnetic lenses to image structures at very small scales. It can resolve details far below the practical resolution of visible-light microscopy.
Eyepiece: The lens system through which an observer views an image in an optical instrument. It magnifies the intermediate image formed by the objective.
Phase-contrast microscopy: A microscopy method that converts differences in optical path length into visible intensity differences. It reveals transparent, unstained cells that have little absorption contrast.
Optical resolution: The ability of an imaging system to distinguish nearby points as separate. Resolution, not magnification alone, determines whether finer specimen details become distinguishable.
Scanning probe microscopy: A family of methods that maps surfaces by scanning a sharp probe across them. It measures surface properties through probe interactions rather than transmitted or reflected light.
Numerical aperture: A dimensionless measure of an optical system’s ability to gather light and resolve detail. A higher value lets the objective collect more light and distinguish finer details.
Differential interference contrast microscopy: A microscopy method that uses polarized light and interference to display specimen gradients as relief-like contrast. It sharpens the appearance of transparent structures without requiring stains.

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