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.