The microscope was invented by the Dutch eyeglass merchant Zacharias Janssen in the late 16th century. This invention broke the limitations of human observation confined to the naked eye. Through one or more lenses, the microscope can magnify and observe tiny objects that are invisible to the naked eye. As a precision instrument, the microscope has been widely applied in fields such as education, medicine, biology, geology, materials science, forensic science, and electronic inspection.

The First Biological Microscope in China

Types of Microscopes

Optical Microscope

Microscopes come in many types, but the term “microscope” commonly refers to an optical microscope in everyday language. Optical microscopes use lenses to magnify objects. The magnification is determined by multiplying the magnification of the objective lens by that of the eyepiece. Currently, most microscopes can achieve magnifications up to 1000X. Due to limitations in resolution, 1600X is considered the maximum magnification for optical microscopes. Resolution is limited by the wavelength of the optical system, which means that beyond a certain magnification, lenses cannot clearly distinguish smaller details.

Depending on their application, optical microscopes can be categorized into various types such as biological microscopes, stereo microscopes, fluorescence microscopes, and metallurgical microscopes.

In our article: How Many Types of Optical Microscopes? We will provide detailed descriptions of the working principles and applications of each type. Optical microscopes are relatively easy to operate and have certain advantages in terms of price. That makes them a good choice for beginners.

Electron Microscope

Electron microscopes use electron beams instead of visible light and come in two types: transmission electron microscopes (TEM) and scanning electron microscopes (SEM). They have similar basic components, including an electron source, lens system, vacuum system, and sample chamber. Building upon the foundation of optical microscopes, which have a resolution of 0.2μm, electron microscopes boast an impressive resolution of 0.2nm. This means they can magnify objects much more than optical microscopes, with an overall magnification reaching up to 200,000X. They are widely used for studying the shapes of molecules and atoms and in the field of nanotechnology. However, because samples must be observed in a vacuum, electron microscopes cannot be used to observe live samples, and they also come with higher purchasing and maintenance costs.

Parts and Functions of a Microscope

Optical Components

Objective Lens

The objective lens is a crucial component of a microscope. It is made up of multiple lenses. Its main function is to magnify the specimen at different levels. Common magnification levels include 4x, 10x, 40x, and 100x. The 100x high-power objective lens typically requires immersion oil for use. It has a lower working distance, and requires more careful handling to avoid damaging the specimen or the lens. In addition to magnification and working distance, numerical aperture (NA) is also an important parameter of the objective lens, determining its optical performance and resolution. The larger numerical aperture brings the higher resolution, which allows for clearer observation of specimens.

Eyepiece

The eyepiece is another crucial optical component installed within the microscope’s head or eyepiece tube. Its role is to further magnify the image produced by the objective lens. Common magnification levels for eyepieces include 10x, but depending on the observation needs, different magnifications such as 5x, 16x, 20x, etc., can be chosen. The field number of the eyepiece determines the field of view during observation, with a larger number indicating a wider field of view.

Illumination

The illumination of a microscope provides uniform and adjustable lighting to the objective lens, resulting in clearer imaging. The main types of light sources include halogen, mercury, and LED lamps. Halogen lamps produce light close to natural light and are relatively inexpensive, suitable for most microscopes, but they generate a significant amount of heat and have a relatively short lifespan. Mercury lamps offer high brightness and can provide a powerful source of ultraviolet light, making them suitable for fluorescence microscopes, but they also have a short lifespan. LEDs have high efficiency, low heat generation, and can produce bright and uniform light sources, but they tend to be relatively more expensive. Different observations and adjustments are determined by another optical component called the condenser.

Condenser

The condenser, composed of multiple lenses, is positioned below the stage of the microscope. Its role is to collect light from the light source, adjust the intensity of illumination, and ensure uniform brightness on the specimen. The aperture diaphragm, an important component within the condenser, allows control over the amount of light entering by adjusting its size, thus affecting the intensity of illumination and numerical aperture. A larger numerical aperture allows more light to enter, enhancing the quality of image formation. Different types of condensers can be chosen based on the type of specimen being observed. Bright-field condensers are used for observing transparent specimens, while dark-field condensers are used for observing opaque or semi-transparent specimens. Specialized types such as phase contrast condensers and polarizing condensers are also available for specific observations.

Mechanical Parts

Base

The base of the microscope is located at the bottom, which provides stability and support.

Arm

The arm connects the base of the microscope to the head, which makes it easier to transport.

Stage

The stage is used to hold the specimen being observed, securing it with clips, and allowing movement of the specimen in the X-Y axes for precise positioning. Some advanced microscopes are equipped with motorized stages, which can enhance efficiency and observation accuracy.

Nosepiece

A nosepiece is used for securing and switching between different magnification of objective lenses. Commonly, it comes in the type of triple nosepiece, quadruple nosepiece or quintuple nosepiece.

Focusing

Focusing consists of coarse and fine adjustments. It is typically located on the side of the arm. First, select the low-power objective lens and use the coarse adjustment knob to bring the specimen into view. Then, switch to the high-power objective lens and use the fine adjustment knob to obtain a clear image.

How to Choose a Microscope?

After understanding the basic concepts of microscopes, there are several factors to consider when choosing the most suitable microscope from various types available in the market:

Determine the Purpose and Type:

For examining biological specimens or pathological analysis, a biological microscope is suitable.

For inspecting circuit boards, small components, or studying insects where high magnification is not required, a stereo microscope is preferred.

For minerals, drugs, or crystal materials, a polarizing microscope is recommended.

For examining metals or alloys, a metallurgical microscope is appropriate.

Magnification and Resolution:

Magnification and resolution are crucial factors of microscopes. Choose the appropriate magnification based on the type of specimen you need to observe.

Cost:

Cost is also a necessary factor to consider when purchasing a microscope. Find a cost-effective microscope that combines your budget. Remember, the highest-priced microscope may not always be the best choice. Instead, focus on selecting a microscope with good optical performance and durability that meets your requirements.