Microscopy Lab Test – Vocabulary Flashcards

Significance of the Microscope

  • The invention of the microscope is considered the single most significant advance in microbiology
    • Without it, humans would have no knowledge of microorganisms or their diversity, roles in disease, ecology, biotechnology, etc.
    • Serves as the foundational tool that enabled germ theory, vaccination, antibiotics, and modern molecular biology.

Types of Microscopes Mentioned

  • Compound light microscope (primary instrument for this course)
  • Dissecting (stereoscopic) microscope
  • Scanning microscope (commonly referring to Scanning Electron Microscope, SEM)
    • Each type varies in magnification range, depth of field, sample preparation requirements, and image production method.

Key Terminology

  • “Light” in “light microscope”
    • Indicates that visible light is the illumination source that transmits the image to your eye.
  • “Compound”
    • Implies the microscope uses more than one lens system (ocular + multiple objective lenses) to achieve higher total magnification while maintaining clarity.

Lens Systems & Magnification

  • Ocular (eyepiece) lens
    • Located in the eyepiece
    • Fixed magnification: 10 \times
  • Objective lenses on student microscopes (3 total)
    1. Low-power objective: 4 \times
    2. Medium-power objective: 10 \times
    3. High-power objective: 40 \times
  • Total magnification (ocular \times objective)
    • Low power: 4 \times 10 = 40
    • Medium power: 10 \times 10 = 100
    • High power: 40 \times 10 = 400

Oil-Immersion Objective (Typically 100 \times) – Why & How

  • Purpose
    • Provides highest useful magnification in a light microscope.
    • Enhances color and clarity (resolution) by minimizing light refraction.
  • Technique
    • A small drop of immersion oil (refractive index ≈ glass) is placed directly on the slide.
    • The 100 \times lens is then carefully lowered into the oil to avoid lens breakage or slide damage.
  • Cleaning
    • After use, wipe hardened oil with lens paper moistened with approved lens cleaner.

Resolution (Resolving Power)

  • Defined as “the ability to clearly distinguish one object from another.”
  • Dependent on wavelength of light and numerical aperture of lenses; improved by oil immersion and proper diaphragm settings.

Carrying & General Care of the Microscope

  • Transport
    • Grasp the arm firmly with one hand.
    • Support the base with the other hand.
    • Tuck microscope toward your body to stabilize.
  • Finishing a Session (4-Step Routine)
    1. Rotate nosepiece to low-power objective.
    2. Lower the stage completely.
    3. Return microscope to cabinet in its assigned slot.
    4. Plug in so the battery/illumination system can recharge (if applicable).
  • Malfunctions
    • Immediately inform the instructor; do not attempt internal repairs.

Cleaning Optics

  • Use lens paper ONLY for oculars and objectives (other materials scratch glass coatings).
  • Remove dust specks on eyepiece with gentle circular motion.
  • For hardened immersion oil, apply lens cleaner to lens paper and wipe carefully.

Focusing Procedure & Correct Use of Knobs

  1. Start under low power.
  2. Begin with the stage at its highest position; slowly lower it while observing through oculars to locate the specimen.
  3. Center the specimen in the field of view.
  4. Use coarse-adjustment knob for initial focus (low power only).
  5. Switch to higher powers without moving the slide; specimen remains centered if properly adjusted.
  6. At medium or high power, use fine-adjustment knob exclusively.
    • Never use coarse adjustment at these powers—risk of crushing slide or lens.

Image Orientation & Movement (Using the “Letter e” Lab)

  • Image appears inverted (flipped upside-down) relative to slide orientation.
  • Moving the slide left makes the image move right in the field.
  • Moving the slide away from you makes the image shift toward you.
  • Demonstrates the physics of lens inversion and is crucial for precise slide manipulation.

Stage & Diaphragm Controls

  • Mechanical stage clips: Secure the slide.
  • Stage control knobs: Permit smooth X-Y movement for scanning.
  • Iris diaphragm: Adjusts light intensity and contrast by controlling the diameter of the light beam passing through the specimen.

Compound Microscope Parts & Their Functions (Comprehensive List)

  • Ocular lens (eyepiece): Magnifies image 10 \times.
  • Body tube: Separates ocular and objective lenses; blocks stray light.
  • Revolving nosepiece: Holds and switches among objective lenses.
  • Low-power objective (4*): Initial scanning and focusing.
  • Medium-power objective (10*): Intermediate magnification; detail observation before high power.
  • High-power objective (40*): High magnification for fine detail.
  • (Oil-immersion objective 100*): Highest magnification; used with oil.
  • Stage: Platform that holds the specimen/slide.
  • Stage clips / mechanical stage: Hold slide firmly in place.
  • Iris diaphragm: Controls amount of transmitted light.
  • Light source / illuminator: Provides illumination through specimen.
  • Coarse-adjustment knob: Large motions of stage/body tube for initial focus.
  • Fine-adjustment knob: Small, precise focus adjustments for sharp image.
  • Arm: Main vertical support; used as a handle.
  • Base: Supports entire microscope; houses electronics or mirror.

Practical, Ethical, & Safety Implications

  • Proper handling prevents equipment damage, saving institutional resources.
  • Accurate focusing and cleaning ensure valid observations, preserving scientific integrity.
  • Reporting malfunctions maintains lab safety for all users.