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The limit of optical resolution in a conventional microscope, the so-called diffraction limit, is in the order of half the wavelength of the light used to image.Thus, when imaging at visible wavelengths, the smallest resolvable features are several hundred nanometers in size (although point-like sources, such as quantum dots, can be resolved quite readily).
Memorial in Jena, Germany to Ernst Karl Abbe, who approximated the diffraction limit of a microscope as = , where d is the resolvable feature size, λ is the wavelength of light, n is the index of refraction of the medium being imaged in, and θ (depicted as α in the inscription) is the half-angle subtended by the optical objective lens (representing the numerical aperture).
The optical microscope, also referred to as a light microscope, is a type of microscope that commonly uses visible light and a system of lenses to generate magnified images of small objects. Optical microscopes are the oldest design of microscope and were possibly invented in their present compound form in the 17th century.
The practical limit to magnification with a light microscope is around 1300×. Higher magnifications are possible, but it becomes increasingly difficult to maintain image clarity as the magnification increases. [17] Bright-field microscopes have low apparent optical resolution due to the blur of out-of-focus material;
A superlens, or super lens, is a lens which uses metamaterials to go beyond the diffraction limit.The diffraction limit is a feature of conventional lenses and microscopes that limits the fineness of their resolution depending on the illumination wavelength and the numerical aperture (NA) of the objective lens.
The shape and texture in each individual grain is made visible through the microscope. [7] As the microscopic scale covers any object that cannot be seen by the naked eye, yet is visible under a microscope, the range of objects that fall under this scale can be as small as an atom, visible underneath a transmission electron microscope. [8]
The near-field optical (NFO) microscope involved a sub-wavelength aperture at the apex of a metal coated sharply pointed transparent tip, and a feedback mechanism to maintain a constant distance of a few nanometers between the sample and the probe. Lewis et al. were also aware of the potential of an NFO microscope at this time. [14]
Differential dynamic microscopy (DDM) is an optical technique that allows performing light scattering experiments by means of a simple optical microscope. [1] [2] DDM is suitable for typical soft materials such as for instance liquids or gels made of colloids, polymers and liquid crystals but also for biological materials like bacteria and cells.