Microscope: Resolution, Magnification, and Contrast

• A microscope is used to see small objects invisible to the naked eye.
• Microscopy is the science of investigating small objects with a microscope.
• Microscopic means invisible without a microscope.
• A good microscope has resolution, contrast, and magnification properties.

Resolution

• Resolution power is the ability to produce separate images of closely placed objects.
• The resolution power of an unaided human eye is about 0.2mm (200µm).
• The resolution of a light microscope is about 0.2µm.
• The resolution of an electron microscope is about 0.5µm.
• Immersion oil enhances resolution due to its higher refractive index than air.

Contrast

• Contrast is improved by staining the specimen.
• Staining enhances cell contrast.

Magnification

• Ocular lens magnification: 10x.
• Objective lens magnifications: Scanning (4x), Low Power (10x), High Power (40x), Oil Immersion (100x).
• Total magnification is calculated by multiplying the objective lens magnification by the ocular lens magnification.
• Scanning field: 40x.
• Low power field: 100x.
• High power field: 400x.
• Oil immersion field: 1000x.

Types of Microscopes

• Simple microscopes use a single lens.
• Compound microscopes use multiple lenses.

Simple Light Microscope

• A magnifying glass is a simple light microscope creating a magnified, virtual, upright image.

Compound Microscope

• Compound scopes are commonly used in research and school labs

Anatomy of a Compound Microscope

• Mechanical parts facilitate adjustment and support
• Inclination Joint: Allows tilting for user convenience.
• Base: Holds the light source, adjustment knobs, and other parts.
• Head: Contains the eyepiece tube and prisms.
  • Monocular: One eyepiece.
  • Binocular: Two eyepieces.
  • Dual head: Two eyepieces, not together.
  • Trinocular: Three eyepieces, usually for camera connection.
• C-shaped arm: Connects the ocular and objective lenses.
• Mechanical stage: Holds slides with clips and has control knobs to move the slide for viewing; includes an aperture for light.
• Stage clips secure the specimen.
• Body tube: Attached to the arm and bears the lenses
  • Draw tube: Holds ocular lenses.
• Revolving/rotating nosepiece: Disc holding objectives.
• Coarse adjustment knob: Elevates or lowers the body tube for approximate focus.
• Condenser adjustment knob: Regulates light intensity.
• Iris diaphragm lever: Controls diaphragm opening.

Magnifying Parts

• Ocular lens: 10x magnification.
  • Microscopes with two eyepieces are binocular.
• Objective lens: 3-5 lenses with varying power (4x, 10x, 40x, 100x).

Illuminating Parts

• Provide light
• Condenser: Focuses light on the slide.
• Iris diaphragm: Controls light through the condenser.
• Light source: Mirror or electric bulb.

Principle of Light Microscopy

• Light passes through the iris diaphragm and specimen.
• The objective gathers the light and forms a magnified image.
• Further magnification by the ocular lens produces the final virtual image.

Dark-Field Microscope

• In dark field microscopy, objects appear bright against a dark background.
• It requires a special dark field condenser.

Dark-Field Microscopy - Principle

• The condenser blocks direct light, allowing only oblique light to pass through the specimen.
• Only reflected light enters the objective lens.
• The specimen is brightly illuminated against a dark background.

Dark-Field Microscopy - Application

• Used to identify living, unstained cells and thin bacteria like spirochetes.

Explore the principles of microscopy, including resolution, contrast, and magnification. Learn how microscopes enable the visualization of tiny objects. Understand the importance of staining techniques to enhance contrast in specimens.