Compound Microscope Anatomy and Operation

The Compound Microscope: Function and Structure

The microscope is fundamentally a system designed to enhance the image of objects. The compound microscope, also known as the optical microscope, is an instrument featuring several lenses. It allows the observation of objects smaller than 0.1 mm, magnifying them up to 1500 times.

Key Systems of the Compound Microscope

The compound microscope is structurally divided into three primary systems:

• The Mechanical System (Support and Movement)
• The Optical System (Magnification)
• The Lighting System (Illumination)

The Mechanical System: Support and Movement

This system includes all parts that provide support and allow for movement and precise adjustment of the microscope components.

• Base or Foot: Provides stability and support for the entire instrument.
• Arm or Column: A mechanical structure that connects and holds the tube and the stage. Its arched shape allows for easy handling and movement.
• Tube: A hollow metal cylinder where the eyepiece is placed at the upper extremity.
• Stage (Platina): A fixed metal piece, often square, where the specimen slide is placed. It features a central aperture through which light passes.
• Stage Clips (Tweezers): Used to hold the specimen slide securely on the stage.
• Mechanical Stage (Movable Carriage): A device with two screws located below the stage, used to precisely move the sample forward, backward, and side-to-side.
• Coarse Adjustment Knob (Macrometric Screw): Permits rapid movement of the tube (or stage) up and down, used for the initial, rough focus adjustment.
• Fine Adjustment Knob (Micrometer Screw): Used for slow, precise movement to correct the initial focus and obtain a clear, sharp image.
• Revolver (Nosepiece): A rotating turret that typically has three or four holes where the objective lenses are screwed in, allowing quick switching between magnifications.

The Optical System: Magnification

The optical system consists of two primary sets of lenses that work together to magnify the image and allow for detailed observation.

• Objectives: These are lens systems mounted on cylinders of different sizes that screw into the revolving nosepiece. They provide the primary magnification. There are typically two main types: Dry Objectives and Immersion Objectives (e.g., oil immersion).
• Eyepiece (Ocular): Located at the top of the tube, the eyepiece is responsible for further enhancing and magnifying the image formed by the objective lens.

Calculating Total Magnification

Total magnification is calculated by multiplying the magnification of the objective lens (AOB) by the magnification of the eyepiece (AOC). For example:

40x (Objective) × 10x (Eyepiece) = 400x (Total Magnification)

The Lighting System: Illumination Control

This system comprises several components that regulate the quantity and quality of light illuminating the specimen preparation, ensuring optimal observation.

• Mirror (or Light Source): Located below the condenser, its function is to direct light toward the specimen preparation.
• Condenser: A lens system placed beneath the stage. Its purpose is to focus and concentrate the light rays onto the specimen.
• Diaphragm (Iris Diaphragm): A disk located below the condenser. Its function is crucial for regulating the amount of light that enters the stage and the objective lens.