Ch.3 The Microscope

Types of Microscopes

• Compound light microscopes

  • Commonly used in veterinary in-house laboratories

• Electron microscopes    

  • Research setting or large human medical facilities

• Fluorescent microscopes

• Phase-contrast microscopes

  • Reference laboratories

• Dark field microscopes

  • Reference laboratories

Compound Light Microscope

• Generate image by using a combination of lenses.

• Optical tube length

  • Distance between the objective lens and the eyepiece

  • 160 mm in most

• Mechanical stage

  • Holds slide

• The mechanical stage controls move the stage back and forth, and left to right

• Coarse and fine focus knobs

  • Used to focus objects

• Substage Condenser

  • Consists of two lenses that focus light from the light source on the object

  • Focused by raising or lowering the condenser

• Aperture Diaphragm (Iris Diaphragm)

  • Opens and closes to control the amount of light illuminating the object.

Compound Light Microscope: Two Separate Lens Systems

• Ocular

  • Located in the eyepiece

  • Usually ×10 magnification

  • Binocular—two eyepieces

  • Monocular—one eyepiece

• Objective

  • 3 to 4 objective lenses, each with different magnification

    • ×4-scanning

    • x10-low

    • x40-high dry

    • x100-oil immersion

    • x50-low oil immersion

Magnification

• Total magnification is calculated by

  • multiplying the ocular magnification by the objective magnification power.

  • Example

    • ×10 (ocular lens) × ×40 (objective lens) = ×400 total magnification

Adjusting the Köhler Illumination

Care and Maintenance

• Follow manufacturer guidelines.

• Use only high quality lens paper to clean lens.

• Solvent is only methanol or specially designed product.

• Excessive oil can be removed with xylene.

• Can dissolve adhesives that secure lens.

• Wipe clean.

• Cover when not used.

• Annual cleaning and adjustment by a professional

• Extra lightbulbs

• Proper location in lab

• Protect from excessive heat and humidity

• Avoid jarring

• Carry with both hands!!!

Calibration

• Important in identifying objects on the slides.

  • Parasite ova often look similar, but size helps to identify them.

• Should be performed on every microscope in the practice.

• Stage micrometer

• Ocular micrometer

• The stage micrometer is a microscope slide etched with a 2-mm line marked in 0.01-mm (10-μm) divisions.

Operating Microscope

Operating Microscope

Digital Microscopy

• Use optics and a camera to capture an image.

• Photomicrographs can be added to patient files.

• Becoming more affordable.

• Evaluate cost, resolution, and quality of images.