Overview
This lecture introduces microscopes, explaining key terms, types, parts, usage techniques, and safety tips to help students effectively observe microscopic specimens.
Key Microscope Concepts
- Magnification is how much larger a microscope can make an object appear.
- Resolution is the ability to distinguish between two separate objects under the microscope.
- Higher resolution means two objects can be seen as distinct even if close together.
Types of Microscopes
- Light microscopes use visible light and are common in classrooms.
- Brightfield microscopes show dark images on a light background.
- Darkfield microscopes use a light stop to display bright objects on a dark background.
- Phase-contrast microscopes show detailed images of living specimens without stains.
- Electron microscopes use electron beams for higher magnification and resolution.
- Transmission Electron Microscopes (TEM) visualize internal structures.
- Scanning Electron Microscopes (SEM) visualize 3D surfaces.
Parts and Functions of a Standard Light Microscope
- The light source and condenser lens focus light on the specimen.
- The diaphragm adjusts the level of light reaching the specimen.
- The stage holds the microscope slide; stage clips secure it.
- Objective lenses (scanning, low power, high power) provide different magnification levels.
- The eyepiece lens further magnifies the image.
- Total magnification = objective lens magnification Ă— eyepiece magnification.
- Coarse focus knob moves the stage up or down for rough focusing.
- Fine focus knob makes small adjustments for precise focusing.
- Stage knobs move the slide side to side for better positioning.
Using a Microscope
- Prepare a wet mount by placing a drop of specimen on a slide and covering it with a cover slip.
- Begin focusing with the lowest magnification and work up to higher magnifications.
- Center the image using stage knobs and adjust focus as needed.
- Clean lenses with lens paper only.
Safety and Best Practices
- Handle microscope slides and cover slips with care; they are fragile.
- Ensure the slide does not touch the objective lens to avoid breakage.
- Always clean lenses with lens paper, not regular tissue.
- After use, remove the slide, turn off the light, lower the stage, switch to lowest power, unplug, and cover the microscope.
Key Terms & Definitions
- Magnification — the process of enlarging the appearance of an object.
- Resolution — the ability to distinguish two objects as separate.
- Objective Lens — lens closest to the specimen, provides primary magnification.
- Eyepiece Lens — lens you look through, adds additional magnification.
- Wet Mount — specimen preparation involving liquid and a cover slip.
Action Items / Next Steps
- Explore online resources on types and uses of light microscopes.
- Practice preparing wet mounts and using all focus/positioning knobs.
- Clean microscope lenses with lens paper after use.
- Review further readings on the physics of resolution and microscope staining techniques.