Microscope Parts and Functions

Overview

This lecture covers the different parts of a compound light microscope, their functions, and the process of focusing and observing specimens using the microscope.

Parts of a Compound Microscope

• The base, called the foot, supports the entire microscope.
• The arm connects the base to the body and holds the lenses.
• The eyepiece lens, located at the top, provides initial magnification (e.g., 10x, 15x, 25x).
• The nose piece is a rotatable disc with multiple objective lenses of different magnifications (e.g., 10x, 45x, 100x).
• Objective lenses further magnify the specimen after the eyepiece.
• The metallic stage holds the specimen slide and has clips for securing the slide in place.
• The light source, which may be an LED bulb or a mirror, illuminates the specimen.
• A plano-concave mirror can focus light onto the specimen when natural or artificial light is used.
• The diaphragm controls the amount of light entering to adjust brightness, similar to the iris in a human eye.

Focusing Mechanism

• Coarse adjustment screw moves the body and lenses up or down to bring the specimen into focus.
• Fine adjustment screw makes small, precise adjustments for clearer viewing tailored to individual eyesight.

Preparing and Observing Specimens

• The specimen is placed on a glass slide and covered with a thin coverslip to protect it.
• Permanent slides, such as those containing preserved algae (e.g., Spirogyra), last a long time.
• The slide is placed on the stage and aligned with the lenses using stage adjustment screws.
• Light passes through an aperture in the stage to illuminate the specimen.
• Final magnification is the product of the eyepiece and objective lens powers (e.g., 25x eyepiece × 100x objective = 2500x).

Key Terms & Definitions

• Eyepiece lens — The lens closest to the eye, providing initial magnification.
• Objective lens — Lenses with various magnifications located on the nose piece that further magnify the specimen.
• Nose piece — Rotatable disc holding multiple objective lenses.
• Stage — Flat platform where the specimen slide is placed.
• Diaphragm — Adjustable part controlling the amount of light reaching the specimen.
• Coarse adjustment screw — Moves the microscope body for large focus changes.
• Fine adjustment screw — Makes small focus adjustments without moving the entire body.
• Plano-concave mirror — Mirror with one flat and one concave side, used to focus light.

Action Items / Next Steps

• Practice identifying the parts and functions of a compound microscope.
• Prepare and observe a slide under different magnifications using both coarse and fine adjustments.