Page 362 - Fundamentals of Light Microscopy and Electronic Imaging

GLOSSARY 345

is focused to position the conjugate image of the light source in the back focal plane
(diffraction plane) of the objective lens. The method provides bright, even illumina-
tion across the diameter of the specimen. 7
Lens equation. In geometrical optics, the equation 1/f 1/a 1/b describing the rela-
tionship between the object distance a and the image distance b for a lens of focal
length f. 46
Light microscope. A microscope employing light as an analytic probe and optics based
on glass lenses to produce a magnified image of an object specimen. 1
Linearly polarized light. A beam of light in which the E vectors of the constituent
waves vibrate in planes that are mutually parallel. Linearly polarized light need not
be coherent or monochromatic. 117
Long-pass filter.A colored glass or interference filter that transmits (passes) long wave-
lengths and blocks short ones. 37
Long working distance lens. An objective lens having a working distance many times
greater than that of a conventional objective lens of the same magnification. A long
working distance lens is sometimes easier to employ and focus, can look deeper into
transparent specimens, and allows the operator greater working space for employing
micropipettes or other equipment in the vicinity of the object. However, the NA and
resolution are less than those for conventional lenses of comparable magnification. 54
Look-up-table (LUT). In image processing, a mathematical function that converts
input values of the signal into output values for display. 284
Lumen. A unit of luminous flux equal to the flux through a unit solid angle (steradian)
from a uniform point source of 1 candle intensity. 284
LUT. See Look-up-table (LUT).
Lux. A unit of illumination equal to 1 lumen per square meter.
Magnitude. See Amplitude of an electromagnetic wave.
Median filter. In image processing, a nonlinear filter for blurring and removing grain.
The filter uses a kernel that is applied to each pixel in the original image to calculate
the median value of a group of pixels covered by the kernel. The median values com-
puted at each pixel location are assigned to the corresponding pixel locations in the
new filtered image. 295
Microchannel plate. A device for amplifying the photoelectron signal in Gen II (and
higher-generation) image intensifiers. The plate consists of a compact array of capil-
lary tubes with metalized walls. Photoelectrons from the intensifier target are accel-
erated onto the plate where they undergo multiple collision and electron amplification
events with the tube wall, which results in a large electron cascade and amplification
of the original photon signal. 251
Modulation contrast microscopy (MCM). A mode of light microscope optics in
which a transparent phase object is made visible by providing unilateral oblique illu-
mination and employing a mask in the back aperture of the objective lens that blocks
one sideband of diffracted light and partially attenuates the 0th-order undeviated
rays. In both MCM and DIC optics, brightly illuminated and shadowed edges in the
three-dimensional relief-like image correspond to optical path gradients (phase gra-
dients) in the specimen. Although resolution and detection sensitivity are somewhat
reduced compared with DIC, the MCM system produces superior images at low
magnifications, allows optical sectioning, and lets you examine cells on birefringent
plastic dishes. 171
Modulation transfer function (MTF). A function showing percent modulation in con-
trast vs. spatial frequency. MTF is used to describe the change in contrast between