43
MICROSCOPE TERMINOLOGY
Abbe Condenser
A two-lens sub-stage condenser located below
the stage of a microscope and functions to collect
light and direct it onto the object being examined.
Its high numerical aperture makes it particularly
suited for use with most medium- and high-
magnification objectives.
Aperture, Numerical (N.A.)
The numerical aperture is an important factor
determining the efficiency of the condenser and
objective. It is represented by the formula: (N.A.
=
η
sin
α
), where
η
is the refractive index of a
medium (air, water, immersion oil etc.) between
the objective and the specimen or condenser,
and
α
is half of the maximum angle at which light
enters or leaves the lens from or to a focused
object point on the optical axis.
Cover Glass Thickness
Transmitted light objectives are designed to
image specimens that are covered by a thin
cover glass (
cover slip
). The thickness of this
small glass piece is now standardized at 0.17
mm for most applications.
Diaphragm, Condenser
A diaphragm, which controls the effective size of
the condenser aperture. A synonym for the
condenser illuminating aperture diaphragm.
Magnification
The number of times by which the size of the
image exceeds the original object. Lateral
magnification is usually meant. It is the ratio of
the distance between two points in the image to
the distance between the two corresponding
points in the object.
Micrometer:
um
A metric unit of length measurement
= 1x10
-6
meters or 0.000001 meters
Nanometer (nm)
A unit of length in the metric system equal to 10
-9
meters.
Phase–contrast (microscopy)
A form of microscopy, which converts differences
in object thickness and refractive index into
differences in image amplitude and intensity.
Real Viewfield
The diameter in millimetres of the object field.
Eyepiece Field of View
Real Viewfield =
Objective Magnification
Example:
Eyepiece field of view
= 20mm
Objective magnification
= 10X
Diameter of the object field = 20/10
=
2.0mm
