FAQ - Microscopes
Microscopes can be fun and educational for the whole family. They have a huge
variety of applications from exploring your environment (i.e., bugs, plants,
stamps, and coins), to inspecting micro circuit boards or examining algae and
blood cells. However, before we explain the different types of microscopes
available, let's explain the instrument.
The microscope consists of the following parts:
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Eyepiece: The eyepiece (sometimes called the 'ocular') is the lens of the
microscope closest to the eye that you look through. It is half of the
magnification equation (eyepiece power multiplied by objective power equals
magnification), and magnifies the image made by the objective lens... sometimes
called the virtual image. Eyepieces come in many different powers. One can
identify which power any given eyepiece is by the inscription on the eyecup of
the lens, such as "5x", "10x", or "15X". Oculars are also designed with
different angles of view; the most common is the wide field (W.F.).
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Eyepiece Holder: This simply connects the eyepiece to the microscope body,
usually with a set-screw to allow the user to easily change the eyepiece to
vary magnifying power.
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Body: The main structural support of the microscope which connects the lens
apparatus to the base.
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>Nose Piece: This connects the objective lens to the microscope body. With a
turret, or rotating nose piece as many as five objectives can be attached to
create different powers of magnification when rotated into position and used
with the existing eyepiece.
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Objective: The lens closest to the object being viewed which creates a
magnified image in an area called the "primary image plane". This is the other
half of the microscope magnification equation (eyepiece power times objective
power equals magnification). Objective lenses have many designs and qualities
which differ with each manufacturer. Usually inscribed on the barrel of the
objective lens is the magnification power and the numerical aperture (a measure
of the limit of resolution of the lens).
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Focusing Mechanism: Adjustment knobs to allow coarse or fine (hundredths of a
millimeter) variations in the focusing of the stage or objective lens of the
microscope.
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Stage: The platform on which the prepared slide or object to be viewed is
placed. A slide is usually held in place by spring-loaded metal stage clips.
More sophisticated high-powered microscopes have mechanical stages which allow
the viewer to smoothly move the stage along the X (horizontal path) and Y
(vertical path) axis. A mechanical stage is a must for high-power observing.
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Illumination Source: The means employed to light the object to be viewed. The
simplest is the illuminating mirror which reflects an ambient light source to
light the object. Many microscopes have an electrical light source for easier
and more consistent lighting. Generally electrical light sources are either
tungsten or fluorescent, the fluorescent being preferred because it operates at
a cooler temperature. Most microscopes illuminate from underneath, through the
object, to the objective lens. On the other hand, stereo microscopes use both
top and bottom illumination.
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Base: The bottom or stand upon which the entire microscope rests or is
connected.
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General Information
The two most important functions of a microscope are magnification and
resolution. Magnification is the power and resolution is the quality of the
viewing.
Magnification: The amount of magnification of a compound microscope is
determined by multiplying the magnifying power of the objective lens by the
magnifying power of the eyepiece. The general rule for magnification is 500x -
1000x the numerical aperture (N.A.) of the objective lens. Anything more is
wasted and is known as "empty magnification". Of equal importance to the
quality of the lenses and eyepieces in magnification is the light source, since
higher powers require a brighter light.
Resolution: More important than magnification is resolution, which is the
ability to discern fine detail in your specimen. Resolution is determined by
the quality of the optics in the eyepiece and objective lens of the microscope.
Types of Microscopes
 Student-Type: This is
the most affordable of the microscope designs. They consist of a single
eyepiece, anywhere from one to three objective lenses, a stage with clips, a
reflective mirror light source, and a maximum of 400 power (x).
 Stereo-Type: This is a
microscope which uses two eyepieces (binocular) and two objective lenses to
create a three-dimensional image. In regards to magnification, these
instruments come in fixed, variable, and zoom designs; with a maximum power of
100x. The most common instruments, however, are 20x - 40x with a large working
area between the objective lens and the stage area. They are most commonly used
as inspection instruments (stamps, coins, circuit boards) or as dissection
microscopes.
 Medical-Biological-Type: These are
more expensive and more sophisticated designs. The eyepieces may be monocular,
binocular, or trinocular, which allows for photo microscopy. The rotating
nosepiece may contain as many as five objective lenses. These microscopes often
include horizontal and vertical, or "coaxial" fine focus adjustments,
mechanical stages, and complex illumination sources. Medical-Biological-type
microscopes may have magnification capabilities of 1000 power, and are mainly
used as laboratory and teaching instruments.
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