Notes on Microscope Usage and Types

General Interaction

• Pinky is conducting an experiment with protists (unicellular organisms) on the kitchen table.

• Protists include Euglena and Paramecium.

• Microscopes are necessary to observe these small, unicellular organisms. 

Key Concepts: Magnification and Resolution

• Magnification: Enlarges an image of the specimen.

• Resolution: Ability to distinguish two separate objects.

• Example: A resolution of 0.2 microns means two objects must be at least 0.2 microns apart to be seen as distinct.

Types of Microscopes

Light Microscopes

• Use light to visualize specimens.

• Brightfield Microscope:

  • Common in classrooms.

  • Produces a darker image on a light background.

• Darkfield Microscope:

  • Uses a light stop to block most light.

  • Shows light objects on a dark background.

• Other types include phase-contrast microscopes (good for live specimens without staining).

Electron Microscopes

• Use electron beams for higher magnification and resolution.

• Transmission Electron Microscopes (TEM): Best for visualizing internal structures.

• Scanning Electron Microscopes (SEM): Best for visualizing the 3D surface of a specimen.

Parts of a Light Microscope

• Light Source: Provides light that passes through the condenser lens.

• Condenser Lens: Focuses light on the specimen.

• Diaphragm: Adjusts the light intensity.

• Stage: Holds the slide; stage clips secure the slide.

• Objective Lenses:

  • Scanning Objective: 4x magnification.

  • Low Power Objective: 10x magnification.

  • High Power Objective: 40x magnification.

• Eyepiece Lens: Magnifies the image, typically 10x.

• Total Magnification: Multiply the objective lens magnification by the eyepiece magnification.

• Example: Scanning lens (4x) × Eyepiece (10x) = 40x total magnification.

Focusing Mechanism

• Coarse Focus Knob: Adjusts the stage dramatically for initial focusing.

• Fine Focus Knob: Adjusts the focus (stage) in smaller increments.

• Stage Knobs: Move the stage side to side (do not affect focus).

Handling the Microscope

• Proper Lifting: One hand under the base, the other holding the arm.

• Avoid water near the microscope as it is electric. 

Preparing a Wet Mount

• Use a pipette to place water on the slide, then cover with a cover slip.

• Avoid air bubbles.

• Stage clips secure the slide.

• Adjust the light level for clarity.

Focusing and Magnification Steps

1. Start with scanning objective lenses (lowest magnification).

2. Focus using coarse focus, then fine-tune with fine focus.

3. Increase magnification (e.g. move to low power for 100x magnification).

4. Fine-tune focus again as magnification increases.

Additional Microscope Tips

1. Fragility: Glass slides and cover slips can break easily.

2. Avoid Crashing Slide: Be careful when moving the stage to prevent crushing the slide against the lens.

3. Lens Cleaning: Use lens paper (not regular tissue) to clean the lens.

Microscope Clean-Up

• Remove the slide, turn off the light, lower the stage, and return the lowest power objective lens.

• Unplug the microscope, wrap the power cord, and cover it.

Additional Techniques

• Use stains or immersion oil to enhance resolution at higher magnifications.

• Microscopes complement life science studies:

  • Study mitosis with onion root tips.

  • Observe stomata on leaves for plant responses.

  • Study osmosis in aquatic plants.

Final Thoughts

• Microscopes open a new world for observation, allowing exploration beyond the visible eye.