The Compound Light Microscope: Structure and Function

The Compound Light Microscope

Introduction

The compound light microscope is an essential tool in biology, allowing scientists and students to observe small specimens that cannot be seen with the naked eye. Understanding the parts and functions of the microscope is fundamental for laboratory work in general biology.

Major Parts of the Compound Light Microscope

• Eyepiece (Ocular Lens): The lens at the top that you look through, typically with 10x magnification.

• Body Tube: Connects the eyepiece to the objective lenses.

• Arm: Supports the body tube and connects it to the base; used for carrying the microscope.

• Base: The bottom support structure of the microscope.

• Objective Lenses: Usually three or four lenses with varying magnifications (e.g., 4x, 10x, 40x, 100x) mounted on a revolving nosepiece.

• Stage: The flat platform where the slide is placed for observation.

• Stage Clips: Hold the slide in place on the stage.

• Coarse Adjustment Knob: Moves the stage up and down for general focusing.

• Fine Adjustment Knob: Allows for precise focusing after using the coarse adjustment.

• Light Source (or Mirror): Illuminates the specimen from below; may be a built-in lamp or a mirror reflecting external light.

• Diaphragm (Iris or Disc): Adjusts the amount of light that reaches the specimen.

• Condenser: Focuses light onto the specimen for clearer viewing.

How a Compound Microscope Works

• The light source illuminates the specimen on the stage.

• Light passes through the condenser and diaphragm to focus and control brightness.

• The objective lens magnifies the image, which is further magnified by the eyepiece.

• Focusing is achieved by adjusting the coarse and fine adjustment knobs.

Magnification and Resolution

• Total Magnification: Calculated by multiplying the magnification of the eyepiece by that of the objective lens.

$\text{Total Magnification} = \text{Eyepiece Magnification} \times \text{Objective Lens Magnification}$

• Resolution: The ability to distinguish two close points as separate; higher resolution provides clearer images.

Proper Use and Care

• Always carry the microscope with one hand on the arm and one under the base.

• Start focusing with the lowest power objective lens.

• Clean lenses only with special lens paper.

• Store the microscope with the lowest power objective in place and the stage lowered.

Example Application

• Microscopes are used to observe cells, tissues, and microorganisms, which are fundamental to understanding biological structure and function.