Microscope Details, Meaning Microscope Article and Explanation Guide

Microscope Guide, Meaning , Facts, Information and Description

A microscope is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. The science of investigating small objects using such an instrument is called microscopy, and the term microscopic means minute or very small, not easily visible with the unaided eye. In other words, requiring a microscope to examine.

The most common type of microscope—and the first to be invented—is the optical microscope. This is an optical instrument containing one or more lenses that produce an enlarged image of an object placed in the focal plane of the lens(es).

Table of contents

1 Simple optical microscope
2 Compound optical microscope

2.1 Stereo microscope
2.2 Special designs

3 Optical resolution
4 History of the microscope
5 Other types of microscopes
6 See Also
7 External links

Simple optical microscope

A simple microscope, as opposed to a standard compound microscope (see below) with multiple lenses, is a microscope that uses only one lens for magnification. Leeuwenhoek's microscopes consisted of a single, small, convex lens mounted on a plate with a mechanism to hold the material to be examined (the sample or specimen). This use of a single, convex lens to magnify objects for viewing is still found in the magnifying glass, the hand-lens, and the lupe.

Compound optical microscope

The diagrams below show compound microscopes. In its simplest form—as used by Robert Hooke, for example—the compound microscope would have a single glass lens of short focal length for the objective, and another single glass lens for the eyepiece or ocular. Modern microscopes of this kind are usually more complex, with multiple lens components in both objective and eyepiece assemblies. These multi-component lenses are designed to reduce aberrations, particularly chromatic aberration and spherical aberration. In modern microscopes the mirror is replaced by a lamp unit providing stable, controllable illumination.

ocular lens or eye-piece
objective turret, or nosepiece
objective lenses
focusing mechanism
(may be a fine focus knob)?
object holder or stage
mirror
diaphragm and condenser

Compound optical microscopes can magnify an image up to 1000X and are used to study thin specimens as they have a very limited depth of field. Typically they are used to examine a smear, a squash preparation, or a thinly sectioned slice of some material. With a few exceptions, they utilize light passing through the sample from below and special techniques are usually necessary to increase the contrast in the image to useful levels (see Contrast methods). Typically, on a standard compound optical microscope, there are three objective lenses: a scanning lens (4x), low power lens (10x), and high power lens (40x). Advanced microscopes often have a fourth objective lens, called an oil immersion lens. To use this lens, a drop of oil is placed on top of the cover slip, and the lens moved into place where it is immersed in the oil. An oil immersion lens usually has a power of 100x. The actual power of magnification is the multiple of the ocular (usually 10x) and the objective lenses being used.

To study the thin structure of metals (see metallography) and minerals, another type of microscope is used, where the light is reflected from the examined surface. The light is fed through the same objective using a semi-transparent mirror.

Stereo microscope

The Stereo, binocular or dissecting microscope is designed differently from the diagrams above, and serves a different purpose. It uses two eyepieces (or sometimes two complete microscopes) to provide slightly different viewing angles to the left and right eyes. In this way it produces a three-dimensional (3-D) visualisation of the sample being examined.

The stereo microscope is often used to study the surfaces of solid specimens or to carry out close work such as sorting, dissection, microsurgery, watch-making, small circuit board manufacture or inspection, and the like.

Special designs

Other types of optical microscope include

The inverted microscope for studying samples from below; useful for cell cultures in liquid.
The student microscope designed for low cost, durability, and ease of use.
The research microscope which is an expensive tool with many enhancements.

Optical resolution

A lens magnifies by bending light (see refraction). Optical microscopes are restricted in their ability to resolve features by a phenomenon called diffraction which, based on the numerical aperture (NA or ) of the optical system and the wavelengths of light used (), sets a definite limit () to the optical resolution. Assuming that optical aberrations are negligible, the resolution () is given by:

Usually, a of 550 nm is assumed, corresponding to green light. With air as medium, the highest practical is 0.95, and with oil, up to 1.5.

Due to diffraction, even the best optical microscope is limited to a resolution of 0.2 micrometers.

History of the microscope

See timeline of microscope technology.

Anton van Leeuwenhoek (1632-1723) is generally credited with bringing the microscope to the attention of biologists, although simple magnifying lenses were being produced in the 1500's, and the magnifying principle of water-filled glass bowls was already known to the Greeks??Romans??(next editor please). Dutch spectacle-makers, Hans Janssen and his son Zacharias Janssen, probably invented the first compound microscope in 1590. Galileo Galilei developed an occhiolino or compound microscope with a convex and a concave lens in 1609. Christiaan Huygens, another Dutchman, developed a simple ocular system in the late 1600's that was achromatically corrected and a huge step forward in microscope development. The Huygens ocular is still being produced to this day, but suffers from a very small field size, and the eye relief is uncomfortably close compared to modern widefield oculars.

Van Leeuwenhoek's microscopes were actually very small simple instruments with a single very strong lens. They were awkard to use but enabled van Leeuwenhoek to see highly detailed images, mainly because a single lens does not suffer the lens faults that are multiplied when using lenses in combination as in a compound microscope. It took about 150 years of optical development before the compound microscope was able to provide the same quality image as van Leeuwenhoek's simple microscopes.

Other types of microscopes

External links

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