microscope

• Microscope


  Instrument used in science laboratories to visualize very minute objects such as cells, microorganisms, producing magnified images with definitive structures
• Microscopes

  • Made up of lenses for magnification, each with their own magnification powers
  • Can view very small specimens and distinguish their structural differences
• Structural parts of a microscope

  • Head
  • Base
  • Arm
• Head


  Also known as the body, it carries the optical parts in the upper part of the microscope
• Base

  Acts as microscope's support, also carries the microscopic illuminators
• Arm

  Part connecting the base and to the head and the eyepiece tube to the base of the microscope, gives support to the head
• Optical parts of a microscope

  • Eyepiece
  • Eyepiece tube
  • Objective lenses
  • Nosepiece
  • Adjustment knobs
  • Stage
  • Aperture
  • Microscopic illuminator
  • Condenser
  • Diaphragm
• Eyepiece

  Also known as the ocular, the part used to look through the microscope, standard magnification is 10x
• Eyepiece tube

  Eyepiece holder, carries the eyepiece just above the objective lens
• Objective lenses

  • Scanner (4x)
  • Low power objectives (10x or 6x)
  • High power objective (45x)
  • Oil immersion objective (100x)
• Nosepiece

  Also known as the revolving turret, holds the objective lenses and can revolve to change magnification
• Adjustment knobs

  • Coarse adjustment knob
  • Fine adjustment knob
• Coarse adjustment knob

  Bigger wheel used to adjust the low power objective in focusing, for rough focusing
• Fine adjustment knob

  Smaller wheel used for delicate focusing with high power and oil immersion objectives, to make the specimen more clear and vivid
• Stage

  Section on which the specimen is placed for viewing, often has mechanical stage to control slide movement
• Aperture


  Hole on the microscope stage, through which the transmitted light from the source reaches the stage
• Microscopic illuminator


  Microscope's light source, located at the base, captures light from an external source
• Condenser


  Lenses used to collect and focus light from the illuminator into the specimen, play a major role in ensuring clear sharp images
• Diaphragm


  Also known as the iris, found under the stage, controls the amount of light that reaches the specimen
• Types of microscopes

  • Light or optical microscopy
  • Electron microscopy
• Light/optical microscopy types

  • Brightfield microscopy
  • Darkfield microscopy
  • Ultraviolet microscopy
  • Fluorescent microscopy
  • Phase contrast microscopy
• Brightfield microscopy


  Most widely used, specimens appear stained or unstained, used for gross morphological features of microorganisms
• Darkfield microscopy


  Uses a special condenser to provide a hollow cone of light, specimen appears bright against a dark background, used for living microorganisms
• Ultraviolet microscopy


  Uses ultraviolet light for greater resolution, allows differentiation of cellular components based on their ability to absorb UV light
• Fluorescent microscopy


  Specimen is treated with a fluorescent dye, appears bright and colored when viewed under UV light, used as a diagnostic technique
• Phase contrast microscopy


  Uses special optical system to distinguish materials that differ slightly in refractive index, used for examining cellular structures in living cells
• Electron microscopy


  Uses a beam of electrons instead of light, has much higher resolving power, used for examining viruses and microbial ultrastructure
• Resolving power


  Ability of the microscope to separate two or more clustered objects so that each can be seen distinctly, function of wavelength and numerical aperture
• Limit of resolution


  Smallest object that can be seen distinctly, determined by shortest wavelength of visible light and maximum aperture
• Numerical aperture


  Indication of the light gathering power of the lens
• Magnification


  Ability of the objective lens to render fine details of an object visible
• Total magnification


  Product of the magnification of the ocular and the objective lens
• Focal length


  Distance between the end of the objective and the object when in focus
• Parfocal


  If one objective is in focus, switching to another objective will still maintain the focus
• Immersion oil


  Used to fill the space between the objective lens and slide, has the same refractive index as glass, used for examining fixed, stained preparations
• Objective lens specifications

  • Focal Length
  • Numerical Aperture
  • Magnification (Objectives)
  • Magnification (Ocular)
  • Total Magnification
• Microscope use and care

  • Hold the arm with one hand, base with other
  • Place at least 6 inches from table edge
  • Clean eyepiece, objectives, condenser, mirror before use
  • Ensure mirror is directed towards light source
  • Start focusing with lowest objective
  • Check for adequate light, adjust mirror and diaphragm
  • Clip slide in place on stage
  • Never tilt if using wet mount or immersion oil
  • Use coarse adjustment for low power, fine for high power
  • Clean oil immersion lens with xylene after use