I. Introduction to Optical Microscopes
An optical microscope is an optical instrument that utilizes the principles of optics to magnify and image tiny objects that cannot be discerned by the naked eye, providing people with optical instruments for extracting information about fine structures.
Structure of Optical Microscopes
(1) Mechanical Parts of Optical Microscopes
Base: It supports the entire microscope.
Pillar: It stands upright above the base, connecting the base and the arm.
Arm: One end is connected to the pillar, and the other end is connected to the tube, serving as the handle for carrying the microscope.
Tube: Attached to the front upper part of the arm, the tube has an eyepiece at the top and an objective turret at the bottom.
Objective turret: Located below the prism housing, it can rotate freely and has 3-4 circular holes for mounting objectives. By rotating the turret, different magnification objectives can be interchanged.
Stage: Positioned below the tube, it comes in square and round shapes and is used to place glass slide specimens.
Adjusters: Two types of screws are installed on the pillar for adjusting the upward and downward movement of the stage.
- a. Coarse Adjuster: Also known as the coarse screw, it rapidly adjusts the distance between the objective and the specimen to bring the image into view. It is typically used when using low-power objectives to locate the specimen quickly.
- b. Fine Adjuster: Also known as the fine screw, it allows for slow elevation or descent of the stage and is mainly used when using high-power objectives to obtain clearer images and observe structures at different levels and depths.
(2) Illumination Part of Optical Microscopes
Positioned below the stage, including the reflector and condenser.
Reflector: Mounted above the base, it can rotate in any direction. It has flat and concave surfaces and reflects light from the light source onto the condenser, which then illuminates the specimen through the aperture. The concave mirror has a stronger light-gathering effect and is suitable for use when the light is weak.
Condenser: Located on the condenser bracket below the stage, it consists of a condenser lens and an aperture, concentrating light onto the specimen to be observed.
(3) Optical Part of Optical Microscopes
Eyepiece: Mounted at the top of the tube, usually equipped with 2-3 eyepieces, each marked with symbols such as 5×, 10×, or 15× to indicate its magnification. Typically, a 10× eyepiece is used.
Objective: Mounted on the rotating turret at the bottom of the tube, typically with 3-4 objectives.
II. Working Principle of Optical Microscopes
The eyepiece and objective of an optical microscope are convex lenses with different focal lengths. The focal length of the objective lens is shorter than that of the eyepiece lens. The objective lens acts as the lens of a projector, forming an inverted and magnified real image of the object. The eyepiece acts as a simple magnifying glass, producing an upright and magnified virtual image of the real image formed by the objective. The object observed through the microscope appears as an inverted magnified virtual image to the human eye. The reflector is used for reflection to illuminate the observed object. The reflector generally has two reflecting surfaces: one is a plane mirror, used when the light is strong; the other is a concave mirror, used when the light is weak, capable of converging light rays.
III. Characteristics of Optical Microscopes
Optical microscopes are characterized by high sensitivity, good precision, good selectivity, simple operation, and convenient sample preparation.
IV. Common Classifications of Optical Microscopes
- Conventional Microscopes: Microscopes in which the image is in the same direction as the object.
- Compound Microscopes: Microscopes in which the image is in the opposite direction to the object.
- Upright Microscopes: The light source of an upright microscope is located below the body, and light passes through a condenser to reach the sample, then through the objective located above the sample, and finally reaches the observer’s eyes or other imaging instruments via a reflector and lenses. This microscope is suitable for observing thin objects that can be sandwiched between glass slides due to the small space between the objective and condenser.
- Inverted Microscopes: The illumination light source and condenser for the bright field are from above the body. The light passes through the condenser to reach the sample, then through the objective located below the sample, and finally reaches the observer’s eyes or imaging instruments via a reflector and lenses. The excitation light source and objective are located at the bottom for fluorescence microscopes.
V. Application Fields of Optical Microscopes
The application scope of optical microscopes is relatively wide, mainly including national defense technology, scientific research, environmental protection, agricultural development, industrial modernization, cultural education, genetic biology, and medical health, among others. Due to its special position and role, the market for optical microscopes is vast, involving a wide range of fields, and we believe that the market development of optical microscopes tomorrow will be even broader.