Overview
The lecture covers the principles, history, types, components, and operation of microscopes, focusing mainly on light microscopes and their usage in biological studies.
Microscopy Basics
- Magnification is the ratio of the image size under the microscope to the object's actual size.
- Resolving power is the ability to distinguish two close points as separate.
- Working distance is the space between the objective lens and the specimen, decreasing with higher magnification.
- Numerical aperture relates to the lens's ability to gather light and affects resolution.
Types of Microscopes
- Simple microscope uses a single convex lens for magnification.
- Compound microscope uses multiple lenses (objective and eyepiece) for greater magnification.
- Electron microscopes use electron beams and include Transmission (TEM) and Scanning (SEM) types for high-resolution imaging.
- Stereomicroscope (dissecting microscope) provides a three-dimensional view with separate optical paths for each eye.
- Scanning probe microscope is used for nanoscale examination.
Microscope Parts & Functions
- Mechanical: base (support), pillar, inclination joint, arm/neck (support and adjustments).
- Stage: holds specimen; stage clips secure slides; stage opening allows light passage.
- Head/body tube: holds lenses and directs light; draw tube holds eyepiece; revolving nosepiece switches objectives.
- Adjustment knobs: coarse (initial focus), fine (precise focus), condenser (light concentration), iris diaphragm (light regulation).
- Magnifying: objectives (4x, 10x, 40x, 100x), eyepiece (10x/15x).
- Illuminating: mirror or electric lamp provides light; condenser and iris diaphragm control light delivery.
Operation & Focusing Steps
- Turn on and set light source to medium intensity.
- Lower the stage, place and center the slide.
- Begin with the scanning objective (4x), use coarse focus, then switch to low power (10x) and fine focus.
- Move up to high power (40x), adjusting only with fine focus.
- For oil immersion (100x), add oil, position objective, and fine focus.
Care and Maintenance
- Carry microscopes with two hands.
- Use only lens paper for cleaning; avoid touching lenses.
- Return settings to low power, lower stage, secure cord, and cover microscope after use.
- Clean with ethanol or methanol on swabs, never regular tissues.
Key Terms & Definitions
- Magnification — Ratio of image size to actual size.
- Resolving Power — Ability to distinguish two points as separate.
- Numerical Aperture — Ratio affecting resolution, based on lens and light amount.
- Working Distance — Space between objective and specimen.
- Objective Lens — Main magnifying lens (4x, 10x, 40x, 100x).
- Eyepiece (Ocular Lens) — Lens viewed through, usually 10x or 15x.
Action Items / Next Steps
- Practice microscope setup and focusing steps with provided specimens.
- Review diagrams of microscope parts and their functions.
- Read further about electron and scanning probe microscopes for exam preparation.