3B Scientific - page 3

. . . g o i n g o n e s t e p f u r t h e r
Information About Microscopes
Course Microscope
Course microscopes are robust, low cost microscopes with basic optical
features that are ideally suited for lessons in school or for beginners in
The barrel is the tube in which the oculars can be placed.
Monocular barrel
: for observation with a single eye.
Binocular barrel
: for stereo observation. This makes the work easier
and less tiring than with a monocular microscope.
Trinocular barrel
: for stereo observation but also allowing for addition
of a camera.
The ocular magnifies the real image thrown by the microscope’s objec-
tive. The diameter of the field of vision, i.e. the area of the slide that
can be viewed at one time, is calculated by dividing the field number by
the scaling factor. Thus for a 10x 18 mm ocular, the viewing field has a
diameter of 1.8 mm.
Objective Revolver
The objective revolver accommodates between 3 and 5 objectives and
makes it possible to change the magnification rapidly when viewing a
An objective produces a real image of the object. The size of the image
is given by the scaling factor (e.g. 10x) and the resolution is determined
by the numerical aperture (e.g. 0.65). The larger the numerical aperture
the more detailed the image produced.
Achromatic objectives provide only a limited amount of correction for
lens aberrations but this is nevertheless sufficient for most uses that
arise in schools. Planar achromatic objectives eliminate image field
curvature and throw an image that is uniformly focused from the centre
of the field of vision to the edge.
Resolution of Objectives
The resolution of an objective is given by the following formula
2 ·
= distance between two points,
= wavelength of the light,
= numerical aperture
Example: numerical aperture = 0.65,
= 0.55 µm, resolution
= 0.423 μm.
Object Stage
The object stage is the shelf upon which slides are placed for observa-
tion through a microscope. Using an x-y cross-table allows the slide to
be moved by specific distances along the x and/or y axes. The scales
mean that once a specific location on the slide has been found, it is
easy to locate it again.
The function of a condenser is to allow for careful adjustment of the
aperture to ensure an optimum compromise between image contrast
and resolution. As the aperture is made smaller, the contrast increases
but the resolution is simultaneously reduced.
Coarse and Fine Focusing
Coarse and fine adjustment gears allow for optimum focusing of an
image. They are mostly fitted along a common axis on either side of the
column leading up from the base.
Microscope slides can be illuminated by means of incandescent tung-
sten lamps, fluorescent tubes, LEDs or halogen lamps. Halogen lamps
are best suited to the task because they provide such intense light.
Fluorescent tubes and LEDs eliminate the problem of slides warming up
due to the heat from the light during longer periods of observation.
Wide field eyepieces
Revolving quadruple nose-
piece with objectives
Object guide
Object stage
Abbé condenser
Seidentopf head
Coaxial adjustment for
coarse and fine focusing
x-y cross-table
Mains switch
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