Contrast in Optical Microscopy When imaging specimens in the optical microscope, differences in intensity and/or color create image contrast, which allows individual features and details of the specimen to become visible. Contrast is defined as the difference in light intensity between the image and the adjacent background relative to the overall background intensity. In general, a minimum contrast value of 0.02 (2 percent) is needed by the human eye to distinguish differences between the image and its background.
Darkfield Illumination The visibility of the faint star light is enormously enhanced against a dark background. This principle is applied in darkfield (also called darkground) microscopy, a simple and popular method for making unstained transparent specimens clearly visible. Such objects often have refractive indices very close in value to that of their surroundings and are difficult to image in conventional brightfield microscopy.
Near-Field Scanning Optical Microscopy Diffraction-limited optical microscopy requires that the spatial resolution of an image is limited by the wavelength of the incident light & by the numerical apertures of the condenser & objective lens systems.The development of near-field scanning optical microscopy (scanning near-field optical microscopy) has allowed for a imaging technique that retains the various contrast mechanisms afforded by optical microscopy methods while attaining spatial resolution beyond the optical diffraction limit
Near-Field Scanning Optical Microscopy: NSOM Probes Near-field scanning optical microscopy can achieve spatial resolution performance beyond the classical diffraction limit by employing a sub-wavelength light source or detector positioned in close proximity to a specimen. Such a sub-wavelength source usually consists of an aperture at the end of a tapered probe, which functions basically as a wave guide. Includes info.: Fiber Probe Fabrication; Pulling Method; Meniscus Etching; Selective Etching; Apertureless and Alternative Probe Designs etc.
Total Internal Reflection Microscopy TIRM is a optical technique for monitoring the instantaneous separation distance between a microscopic sphere & a flat plate. Changes in distance as small as 1 nm can be detected. Includes information on: Scattering Intensity I is Related to Elevation h ; apparatus.
Watching Molecular Motors at Work by Video-Enhanced Light Microscopy The light microscope allows dynamic biological processes to be imaged in their native (i.e., aqueous) environment with relatively high temporal resolution. However, the diffraction-limited resolution is low. When working at or beyond the diffraction-limited resolution of the LM, a disadvantage of fluorescence imaging is the relatively low signal-to-noise (S/N) ratio of the images. However, this can be increased significantly by video and computer technology.
