Microscopy

Magnification: How many times larger the image is compared to the actual object.

Resolution: The ability to distinguish two very close points as separate and clear.

• Uses visible light and glass lenses to magnify specimens.
• Can view living cells.
• Maximum useful magnification: ~×1500.
• Resolution: lower than electron microscopes → cannot see very small structures like ribosomes or plasmids.
• lower than electron microscopes → cannot see very small structures like ribosomes or plasmids.

• Eyepiece lens – usually ×10.
• Objective lenses – e. g., ×4, ×10, ×40.
• Coarse focus knob – large adjustments.
• Fine focus knob – sharpens image.
• Stage – holds slide.
• Light source / mirror – illuminates’ specimen.
• Iris diaphragm – controls light intensity.

• Specimen must be thin and transparent to allow light through.
• Place specimen in water or saline (NaCl solution) for live cells.
• Add stain if needed (e. g., iodine for plant cells).
• Lower coverslip gently using a mounted needle to avoid air bubbles.

Formula triangle to find magnification/image size/actual size:

• The magnification of an image can be calculated by simple formula.
• Magnification = size of the image / actual size of the object.

• You must cover the part of the triangle to find and follow the equation that is left behind.
• For example, to find out image size, the formula is magnification x actual size.
• To find out magnification, the formula is image size / actual size.
• To find out actual size of the cell, the formula is image size / magnification.

• Total magnification = eyepiece × objective.
• For size calculations:
• I = A X M, where:
• I = image size
• A = actual size
• M = magnification
• Rearranged:

Important: Use the same units for I and A before calculating.

• Microscopy often uses nm, μm, mm. Conversion chain:
• nm → μm: ÷1000
• μm → mm: ÷1000
• mm → cm: ÷10
• cm → m: ÷100
• Example: 2,500,000 nm → 2500 μm → 2.5 mm → 0.25 cm → 0.0025 m.

• Use electrons instead of light → much higher magnification and resolution.
• Types:
• TEM (Transmission Electron Microscope) – passes electrons through specimen → internal details.
• SEM (Scanning Electron Microscope) – electrons scan surface → 3D surface images.
• Key features:
• Magnification up to ×2,000,000.
• High resolution → can see ribosomes, plasmids, viruses.
• Cannot view living cells (vacuum required).
• Electron microscope has higher resolution, revealing more and clearer detail.

• Allows study of cells, microorganisms, and subcellular structures.
• Used in medical diagnosis, forensics, research, and education.
• Enables observation of structures invisible to the naked eye.