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The interpretation of dark-field images must be done with great care, as common dark features of bright-field microscopy images may be invisible, and vice versa. In general the dark-field image lacks the low spatial frequencies associated with the bright-field image, making the image a high-passed version of the underlying structure.
Bright-field microscopy (BF) is the simplest of all the optical microscopy illumination techniques. Sample illumination is transmitted (i.e., illuminated from below and observed from above) white light , and contrast in the sample is caused by attenuation of the transmitted light in dense areas of the sample.
At the beginning of the 20th century, R. A. Zsigmondy introduced the ultramicroscope as a new illumination scheme into dark-field microscopy. Here sunlight or a white lamp is used to illuminate a precision slit. The slit is then imaged by a condensor lens into the sample to form a lightsheet.
Dark field and phase contrast microscopies operating principle. The basic principle to make phase changes visible in phase-contrast microscopy is to separate the illuminating (background) light from the specimen-scattered light (which makes up the foreground details) and to manipulate these differently.
This eliminates a typical weaknesses in conventional STEM operation as STEM bright-field and dark-field detectors are placed at fixed angles and cannot be changed during imaging. [27] With a 4D dataset bright/dark-field images can be obtained by integrating diffraction intensities from diffracted and transmitted beams respectively. [25]
In microscopy transillumination refers to the illumination of a sample by transmitted light. In its most basic form it generates a bright field image, and is commonly used with transillumination techniques such as phase contrast and differential interference contrast microscopy.
In the field of transmission electron microscopy, phase-contrast imaging may be employed to image columns of individual atoms; a more common name is high-resolution transmission electron microscopy. It is the highest resolution imaging technique ever developed, and can allow for resolutions of less than one angstrom (less than 0.1 nanometres).
Dark-field X-ray microscopy (DFXM [1] or DFXRM [2]) is an imaging technique used for multiscale structural characterisation. It is capable of mapping deeply embedded structural elements with nm-resolution using synchrotron X-ray diffraction -based imaging.