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Köhler Illumination
Köhler illumination is a method of specimen illumination used for transmitted and reflected light (trans- and epi-illuminated) optical microscopy. Köhler illumination acts to generate an even illumination of the sample and ensures that an image of the illumination source (for example a halogen lamp filament) is not visible in the resulting image. Köhler illumination is the predominant technique for sample illumination in modern scientific light microscopy. It requires additional optical elements which are more expensive and may not be present in more basic light microscopes. History and motivation Prior to Köhler illumination critical illumination was the predominant technique for sample illumination. Critical illumination has the major limitation that the image of the light source (typically a light bulb) falls in the same plane as the image of the specimen, i.e. the bulb filament is visible in the final image. The image of the light source is often referred to as the filament ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Illumination (lighting)
Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing daylight. Daylighting (using windows, skylights, or light shelves) is sometimes used as the main source of light during daytime in buildings. This can save energy in place of using artificial lighting, which represents a major component of energy consumption in buildings. Proper lighting can enhance task performance, improve the appearance of an area, or have positive psychological effects on occupants. Indoor lighting is usually accomplished using light fixtures, and is a key part of interior design. Lighting can also be an intrinsic component of landscape projects. History With the discovery of fire, the earliest form of artificial lighting used to illuminate an area were campfires or torches. As early as 400,000 years ago, fire was kindled ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Contrast (vision)
Contrast is the contradiction in luminance or colour that makes an object (or its representation in an image or display) distinguishable. In visual perception of the real world, contrast is determined by the difference in the colour and brightness of the object and other objects within the same field of view. The human visual system is more sensitive to contrast than absolute luminance; we can perceive the world similarly regardless of the huge changes in illumination over the day or from place to place. The maximum ''contrast'' of an image is the contrast ratio or dynamic range. Images with a contrast ratio close to their medium's maximum possible contrast ratio experience a ''conservation of contrast'', wherein any increase in contrast in some parts of the image must necessarily result in a decrease in contrast elsewhere. Brightening an image will increase contrast in dark areas but decrease contrast in bright areas, while darkening the image will have the opposite effect. B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hoffman Modulation Contrast Microscopy
Hoffman modulation contrast microscopy (HMC microscopy) is an optical microscopy Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultravio ... technique for enhancing the contrast in unstained biological specimens. The technique was invented by Robert Hoffman in 1975. Like differential interference contrast microscopy (DIC microscopy), contrast is increased by using components in the light path which convert phase gradients in the specimen into differences in light intensity that are rendered in an image that appears three-dimensional. The 3D appearance may be misleading, as a feature which appears to cast a shadow may not necessarily have a distinct physical geometry corresponding to the shadow. The technique is particularly suitable for optical sectioning at lower magnifications.Douglas B. M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polarized Light Microscopy
Polarized light microscopy can mean any of a number of optical microscopy techniques involving polarized light. Simple techniques include illumination of the sample with polarized light. Directly transmitted light can, optionally, be blocked with a polariser orientated at 90 degrees to the illumination. More complex microscopy techniques which take advantage of polarized light include differential interference contrast microscopy and interference reflection microscopy. Scientists will often use a device called a polarizing plate to convert natural light into polarized light. These illumination techniques are most commonly used on birefringent samples where the polarized light interacts strongly with the sample and so generating contrast with the background. Polarized light microscopy is used extensively in optical mineralogy. History Although the invention of the polarizing microscope is typically attributed to David Brewster around 1815, Brewster clearly acknowledges the prio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spatial Filter
A spatial filter is an optical device which uses the principles of Fourier optics to alter the structure of a beam of light or other electromagnetic radiation, typically coherent laser light. Spatial filtering is commonly used to "clean up" the output of lasers, removing aberrations in the beam due to imperfect, dirty, or damaged optics, or due to variations in the laser gain medium itself. This filtering can be applied to transmit a pure transverse mode from a multimode laser while blocking other modes emitted from the optical resonator. The term "filtering" indicates that the desirable structural features of the original source pass through the filter, while the undesirable features are blocked. An apparatus which follows the filter effectively sees a higher-quality but lower-powered image of the source, instead of the actual source directly. An example of the use of spatial filter can be seen in advanced setup of micro-Raman spectroscopy. In spatial filtering, a lens is used to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nonimaging Optics
Nonimaging optics (also called anidolic optics)Roland Winston et al., ''Nonimaging Optics'', Academic Press, 2004 R. John Koshel (Editor), ''Illumination Engineering: Design with Nonimaging Optics'', Wiley, 2013 is the branch of optics concerned with the optimal transfer of light radiation between a source and a target. Unlike traditional imaging optics, the techniques involved do not attempt to form an image of the source; instead an optimized optical system for optimal radiative transfer from a source to a target is desired. Applications The two design problems that nonimaging optics solves better than imaging optics are: * solar energy concentration: maximizing the amount of energy applied to a receiver, typically a solar cell or a thermal receiver * illumination: controlling the distribution of light, typically so it is "evenly" spread over some areas and completely blocked from other areas Typical variables to be optimized at the target include the total radiant flux, the angu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bertrand Lens
A phase telescope or Bertrand lens is an optical device used in aligning the various optical components of a light microscope. In particular it allows observation of the back focal plane of the objective lens and its conjugated focal planes. The phase telescope/Bertrand lens is inserted into the microscope in place of an eyepiece to move the intermediate image plane to a point where it can be observed. Phase telescopes are primarily used for aligning the optical components required for Köhler illumination and phase contrast microscopy. For Köhler illumination the light source and condenser diaphragm should appear in focus at the back focal plane of the objective lens. For phase contrast microscopy the phase ring (at the back focal plane of the objective) and the annulus (at the back focal plane of the condenser lens) should appear in focus and in alignment. Bertrand lenses find use in creating interference figures and assisting in aligning a microscope to generate interference fig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase Telescope
A phase telescope or Bertrand lens is an optical device used in aligning the various optical components of a light microscope. In particular it allows observation of the back focal plane of the objective lens and its conjugated focal planes. The phase telescope/Bertrand lens is inserted into the microscope in place of an eyepiece to move the intermediate image plane to a point where it can be observed. Phase telescopes are primarily used for aligning the optical components required for Köhler illumination and phase contrast microscopy. For Köhler illumination the light source and condenser diaphragm should appear in focus at the back focal plane of the objective lens. For phase contrast microscopy the phase ring (at the back focal plane of the objective) and the annulus (at the back focal plane of the condenser lens) should appear in focus and in alignment. Bertrand lenses find use in creating interference figures and assisting in aligning a microscope to generate interference fig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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