Page 365 - Fundamentals of Light Microscopy and Electronic Imaging

348 GLOSSARY

Panning. In electronic imaging, the movement of the camera to bring into view portions
of an object field that cannot be included in a single image frame; in image processing,
the relative displacement of one image over another for purposes of alignment. 314
Paraboloid condenser. A high numerical aperture condenser for dark-field microscopy
having a reflective surface that is a segment of a figure of revolution of a parabola.
The steeply pitched illumination cone produced by the condenser is suitable for dark-
field examination with high-power oil immersion objectives. 114
Parallel register. In CCD cameras, the extended array of imaging (and storage) pixels
of the imaging area of a CCD device. Columns of pixels in the parallel register
deliver their charge packets (photoelectrons) to a separate serial register from which
the image signal is read and digitized by the camera electronics. 261
Parfocal. The property of having the same distance between the specimen and the
objective turret of the microscope. With parfocal lenses, one can focus an object with
one lens and then switch to another lens without having to readjust the focus dial of
the microscope. 9
Particle wave. In phase contrast and other modes of interference microscopy, the wave
(P wave) that results from interference between diffracted and surround waves in the
image plane, and whose amplitude is different from that of the surrounding back-
ground, allowing it to be perceived by the eye. See also Diffracted wave and Sur-
round wave. 101
Peltier thermoelectric device. A compact bimetallic strip that becomes hot on one sur-
face and cold on the other during the application of a current. Peltier devices are com-
monly used in CCD cameras where it is necessary to quickly and efficiently cool the
CCD 50–60°C below ambient temperature in a compact space. 267
Phase. Relative position in a cyclical or wave motion. Since one wavelength is
described as 2 radians or 360°, the phase of a wave is given in radians or degrees or
fractions of a wavelength. 63
Phase contrast microscopy. A form of interference microscopy that transforms differ-
ences in optical path in an object to differences in amplitude in the image, making trans-
parent phase objects appear as though they had been stained. Surround and diffracted
rays from the specimen occupy different locations in the diffraction plane at the back
aperture of the objective lens where their phases are differentially manipulated in order
to generate a contrast image. Two special pieces of equipment are required: a condenser
annulus and a modified objective lens containing a phase plate. Because the method is
dependent on diffraction and scattering, phase contrast optics differentially enhance the
visibility of small particles, filaments, and the edges of extended objects. The technique
allows for examination of fine details in transparent specimens such as live cells. 97
Phase gradient. In interference microscopy, the gradient of phase shifts in an image
corresponding to optical path differences in the object. 154
Phase object. Objects that shift the phase of light as opposed to those that absorb light
(amplitude objects) as the basis for image formation. See also Amplitude object. 97
Phase plate. In phase contrast microscopy, a transparent plate with a semitransparent
raised or depressed circular annulus located at the rear focal plane of a phase contrast
objective. The annulus reduces the amplitude of background (0th order) waves and
advances or retards the phase of the 0th-order component relative to diffracted
waves. Its action is responsible for the phase contrast interference image. 105
Phase or centering telescope. See Bertrand lens.
Phosphorescence. The relatively slow ( 10 9 s) emission of photons after excitation
of a material by light or other radiation source. 181