The Compound Microscope

The Compound Microscope

Parts of a Microscope

Mechanical Parts

Illuminating Parts

Magnifying Parts

Mechanical Parts

Illuminating Parts

Magnifying Parts: The Objectives

Terminologies

Total Magnification: numerical value of how many times the specimen in focus is magnified

Resolution or Resolving Power: ability to distinguish two adjacent points as distinct or separate. Increase magnification without increased resolution

is not useful because the image may be unclear or fuzzy.

The resolving power is a function of the: numerical aperture and wavelength

Terminologies

Numerical Aperture: is a mathematical expression of the size of the beam of light which an objective can utilize. The higher the NA, the greater the detail the objective will reveal. LPO – 0.6, HPO – 0.8, OIO – 1.25

Limit of Resolution: smallest distance by which two objects can be separated and still be distinguishable as 2 separate objects.

Working distance: distance between the lens of the objective and the cover slip.

Principle of the Oil Immersion Objective

The front lens of the OIO is immersed in immersion oil which fills the space between the front of the objective and the slide.

Immersion oil has the same refractive index as glass and also increases the NA of the lens.

Light coming through the glass slide passes straight through the oil into the glass lens of the objective without deflection of light waves.

Types of Microscopes

Light Microscope: visible light spectrum (400nm-700nm) passes through the specimen then through series of lenses which reflect light in such a manner that results in the magnification of the specimen

Limit of resolution: 200nmMaximum magnification:

2000x

Types of Microscopes

Bright-Field Microscope: the field of vision is light and the microorganisms appear dark because they absorb some of the light. Staining increases the light-

absorbing ability of the microorganism resulting to greater contrast and color differentiation.

Types of Microscopes

Dark-Field Microscope: has a special condenser that fits into the substage, resulting in a dark background against objects which are brilliantly illuminated or appear as bright refractile bodies. Useful in the examination of

unstained live microorganisms.

Types of Microscopes

Fluorescence Microscope: makes use of the principle that certain dyes when exposed to uv light alter the wavelength of this light and become luminous (flouresce). Best used for immunological and

serological studies

Phase Contrast: used in studying living unstained cells. A conventional light microscope fitted with a phase contrast objective and phase contrast condenser.

Types of Microscopes

Electron Microscope: provides tremendous useful magnification because of the much higher resolution obtainable with the extremely short wavelength of the electron beam used to magnify the specimen. Transmission EM: two dimensional Scanning EM: three dimensional

Limitations of EM: specimen may not be examined in living state, morphological characteristic of the specimen may be altered, low penetrating power of the electron beam necessitates thin sections of the cell.

Specimen viewed

Specimen viewed