Page 358 - Fundamentals of Light Microscopy and Electronic Imaging

GLOSSARY 341

Fluorite or semiapochromat lens. Objective lenses made of fluorite or Ca F, a highly
2
transparent material of low color dispersion. The excellent color correction afforded
by simple fluorite elements accounts for their alternative designation as semiapo-
chromats. The maximum numerical aperture is usually limited at 1.3. 53
Fluorochrome. A dye or molecule capable of exhibiting fluorescence. 181
Fluorophore. The specific region or structural domain of a molecule capable of
exhibiting fluorescence. Examples include the fluorescein moiety in a fluorescein-
conjugated protein and the tetrapyrrole ring in chlorophyll. 181
Focal length. The distance along the optic axis between the principal plane of a lens and
its focal plane. For a simple converging (positive) lens illuminated by an infinitely
distant point source of light, the image of the point lies precisely one focal length
away from the principal plane. 43, 45
Focal ratio or f-number. The ratio of the focal length of a lens to the diameter of its
aperture. 65
Fovea. A 0.2–0.3 mm diameter spot in the center of the macula on the retina that lies on
the optic axis of the eye and contains a high concentration of cone cell photorecep-
tors for color vision and visual acuity in bright light conditions. 24
Frame accumulation. In electronic imaging, the method of adding together a number
of image frames to create a brighter image with improved signal-to-noise ratio. 249
Frame averaging or Kalman averaging. In electronic imaging, the method of averag-
ing a number of raw image frames to reduce noise and improve the signal-to-noise
ratio. The signal-to-noise ratio varies as the square root of the number of frames aver-
aged. 217
Frame grabber board. In electronic imaging, the computer board that determines
the frame memory, a remote access memory for storing the pixel values comprising
an image. Grabbing is the process of acquiring and storing an image into a frame
buffer. 235
Frame-transfer CCD. A CCD whose pixel array is divided into two equal halves. One
section is uncovered and contains active photosites; the other area is masked with a
light-shielding metal film and acts as a storage site. This design of CCD speeds
image capture, because readout of the storage site and acquisition at the image site
occur simultaneously and because the camera can work without a shutter. 267
Frequency of vibration. The number of periods per unit time or unit distance of an
electromagnetic wave. 16
Full-frame CCD camera. A CCD design in which all of the pixels function as active
photosites. 267
Full wave plate. In polarization optics, a birefringent plate (retarder) capable of intro-
ducing an optical path length difference between O and E rays equivalent to a full
wavelength of light. Since the unique wavelength emerges with a linearly polarized
waveform, positioning the plate diagonally between two crossed polars under condi-
tions of white light illumination extinguishes the linearly polarized wavelength,
resulting in the visual perception of an interference color. A first-order red plate
shows a first-order red interference color because 551 nm green wavelengths have
been removed. 141
Full width at half maximum (FWHM). A parameter describing the spectral range of
transmitted wavelengths of a bandpass filter. The cut-on and cut-off boundaries are
defined as the wavelengths giving 50% of maximum transmittance of the filter. A
FWHM of 20 indicates that the transmitted bandwidth spans 20 nm. Also called the
half bandwidth (HBW). 37
FWHM. See Full width at half maximum (FWHM).