Microscope: Tiny World
2008-08-22

Microscope is an instrument used to obtain an enlarged image of a small object. The image may be seen, photographed, or sensed by photocells or other receivers, depending upon the nature of the image and the use to be made of the information of the image. A simple microscope, hand lens, or magnifier usually is a round piece of transparent material, ground thinner at the edge than at the center, which can form an enlarged image of a small object. Commonly, simple microscopes are double convex or Plano convex lenses, or systems of lenses acting together to form the image. The compound microscope utilizes two lenses or lens systems. One lens system forms an enlarged image of the object and the second magnifies the image formed by the first. The total magnification is then the product of the magnifications of both lens systems (see illustration).

The typical compound microscope consists of a stand, a stage to hold the specimen, a movable body-tube containing the two lens systems, and mechanical controls for easy movement of the body and the specimen. The lens system nearest the specimen is called the objective; the one nearest the eye is called the eyepiece or ocular. A mirror is placed under the stage to reflect light into the instrument when the illumination is not built into the stand. For objectives of higher numerical aperture than 0.4, a condenser is provided under the stage to increase the illumination of the specimen. Various optical and mechanical attachments may be added to facilitate the analysis of the information in the doubly enlarged image History of the microscope

In ancient and classical civilizations, people recognized the magnifying power of curved pieces of glass. By the year 1300, these early crude lenses were being used as corrective eyeglasses. In the seventeenth century Robert Hooke published his observations of the microscopic examination of plant and animal tissues. Using a simple two-lens compound microscope, he was able to discern the cells in a thin section of cork. The most famous microbiologist was Antonio van Leeuwenhoek. Using a single-lens microscope that he designed, Leeuwenhoek described microorganisms in environments such as pond water. His were the first descriptions of bacteria and red blood cells. By the mid-nineteenth century, refinements in lens grinding techniques had improved the design of light microscopes. Still, advancement was mostly by trial and error, rather than by a deliberate crafting of a specific design of lens. It was Ernst Abe who first applied physical principles to lens design. Abe combined glasses that bent light beams to different extents into a single lens, reducing the distortion of the image. The resolution of the light microscope is limited by the wavelength of visible light. To resolve objects that are closer together, the illuminating wavelength needs to be smaller. The adaptation of electrons for use in microscopes provided the increased resolution. In the mid-1920s, Louis de Broglie suggested that electrons, as well as other particles, should exhibit wavelike properties similar to light. Experiments on electron beams a few years later confirmed this hypothesis. This was exploited in the 1930s in the development of the electron microscope. Types of microscope "Microscopes" can largely be separated into three classes: optical theory microscopes, electron microscopes, and scanning probe microscopes. (A) Optical microscopes Optical microscopes, through their use of visible wavelengths of light, are the simplest and hence most widely used type of microscope. Optical microscopes use refractive lenses, typically of glass and occasionally of plastic, to focus light into the eye or another light detector. Typical magnification of a light microscope is up to 1500x with a theoretical resolution limit of around 0.2 micrometers or 200 nanometers. Specialized techniques (e.g., scanning co focal microscopy) may exceed this magnification but the resolution is an insurmountable diffraction limit. Various wavelengths of light are sometimes used for special purposes, for example, in the study of biological tissue. Ultraviolet light is used to illuminate the object being viewed in order to excite a fluorescent dye which then emits visible light. Infrared light is used to study thick slices of biological tissue because infrared light's low diffraction coefficient permits viewing deeper into tissue. Other microscopes which use electromagnetic wavelengths not visible to the human eye are often called optical microscopes. The most common of these, due to its high resolution yet no requirement for a vacuum like electron microscopes, is the x-ray microscope. (B) Electron microscopes Electron microscopes, which use beams of electrons instead of light, are designed for very high magnification usage. Electrons, which can be accelerated to produce a much smaller wavelength than visible light, allow a much higher resolution. The main limitation of the electron beam is that it must pass through a vacuum as air molecules would otherwise scatter the beam. Instead of relying on refraction, lenses for electron microscopes are specially designed electromagnets which generate magnetic fields that are approximately parallel to the direction that electrons travel. The electrons are typically detected by a phosphor screen, photographic film or a charge-coupled device (CCD). (C) Scanning probe microscope In scanning probe microscopy (SPM), a physical probe is used either in close contact to the sample or nearly touching it. By raftering the probe across the sample, and by measuring the interactions between the sharp tip of the probe and the sample, a micrograph is generated. The exact nature of the interactions between the probe and the sample determines exactly what kind of SPM is being used. Because this kind of microscopy relies on the interactions between the tip and the sample, it generally only measures information about the surface of the sample. A variation of the SPM is the SECM (Scanning Electrochemical Microscope). A SECM images a sample in a similar manner as a SPM but the sample is in an electrolyte solution with the SECM using electrochemically active tip (D) Other microscopes Scanning acoustic microscopes use sound waves to measure variations in acoustic impedance. Similar to Sonar in principle, they are used for such jobs as detecting defects in the subsurface of materials including those found in integrated circuits.

Below is a microscope made by Poway Optics & Electronics Co., Ltd

Product Description: Digital Biological Microscope DN-PW117M Feature: 1.360 degree rotation of Eyepiece Tube 2. with Interpupilary Distance 48mm-75mm 3. Built-in Digital System, 1/2'' CMOS Chip with 1.3M pixel 4.90% real image can be seen through Digital System Specification: - Seidentofp type binocular head, inclined at 30 degree - Built-in digital camera system: 1/2" CMOS Chip, 1.3M Pixel (1280X1024) USB2.0, for WINDOWS 2000/XP/VISTA With Software - WF10X/18mm - Achromatic objective: 4x, 10x, 40x, 100 xs - Backward quadruple nosepiece - Double layers mechanical stage 132x142/75x40mm - Coaxial coarse & fine focus adjustment system Range 24mm, fine division 0.004mm - NA1.25 Abe condenser with iris diaphragm and filter - Halogen lamp 6V/20W, brightness adjustable. Optional Accessory: Phase Contrast Kit Dark Field Attachment Polarization Attachment Standard accessory: 6V/20W spare halogen lamp --- 1pc Blue ground glass filter---1pc Operation Manual---1pc