Owen G. Sunga, MD© Ryan Barrow 20081

The Microscope

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Objectives Know the Basics

Parts and Functions Use Types and Differences

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Historical Timeline 1609 – Galileo Galilei develops a

compound microscope with a convex and a concave les.

1665 – Robert Hooke publishes Micrographia and coins the word cell for structures he discovers in cork bark

1674 – Anton van Leeuwenhoek improves on a simple microscope for viewing biological specimens

1931 – Ernst Ruska starts to build the first electron microscope

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Types of Microscopes

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Types of Microscopes I Compound

Microscope Light microscope that

has two converging lens systems: the objective and the eyepiece

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Types of Microscopes II Electron Microscope

Any class of microscopes that use electrons instead of light to form images of very small objects such as individual parts of small living things

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Types of Microscopes III Transmission Electron Microscope

Microscope used to reveal the internal structure of microbial and cell types.

Scanning Electron Microscope The electron beam is scanned, or swept over a

metal coating to form a three-dimensional image.

Scanning Tunneling Microscope Can produce three-dimensional images of

individual molecule and atoms, as well as movies

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The Compound Microscope

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The Compound Microscope Base

Supporting structure that generally contains the source

Condenser Converges light

beams to pass through the specimen

Iris Diaphragm Controls the amount

of light passing through the specimen

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Compound Microscope II Objective Lens

Magnifies image Body Tube (Arm)

Conveys light to the ocular lens

Ocular Lens (Eye piece) Magnifies the image from

the objective. A microscope with one ocular lens (eyepiece) is monocular; a microscope with two ocular lenses is binocular

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Compound Microscope III Mechanical Stage

Allows precise control in moving the slide

Coarse Adjustment Knob used to locate

specimen Fine Adjustment

Knob used to bring the specimen into sharp focus

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Compound Microscope IV Total magnification

Calculated by multiplying the magnifying power of the objective lens by the magnifying power of the ocular lens. Increased magnification is no value unless good resolution can also be maintained.

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Properties of Light

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Properties of Light Reflection

Light strikes an object and bounces back

Transmission Passage of light

through an object Must be one of these 2

for a microscope Absorption

Taken up by that object and used as energy Photosynthesis

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Properties of Light II Refraction

Bending of light as it passes through one medium to another of different density

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Properties of Light II Diffraction

Occurs when light rays are bent as they pass through a small opening, such as a hole, a slit, a space between two adjacent cellular structures, or a small, high powered, magnifying lens in a microscope. The bent light rays distort the image obtained and limit the usefulness of the light microscope.

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Immersion Oil Immersion Oil

Same index of refraction as glass Used to replace air to prevent refraction at a

glass-air interface Works as a “secondary lens” Allows a clearer and larger image

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Proper Procedures1. Carry the microscope

with one hand under the base while grasping the arm with the other hand

2. Place microscope ~5 inches from the edge of the table

Be careful of the cord when moving around the lab tables!!

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Proper Procedures

3. Rotate the nosepiece to obtain the proper objective lens

Make sure the lens clicks into place!!

4. Look through the eyepiece and switch on the lamp

This is your field of view!

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Proper Procedures

5. Place slide on stage, center specimen over stage

6. Locate specimen on low power using coarse adjustment

7. Carefully switch to medium or high power

8. Focus image with fine adjustment

Avoid damaging slide! Do not use course adjustment with high power!

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Storing the Microscope

1. the 10X objective is in place

2. the stage is all the way down

3. the power is off

4. the cord is wrapped around

the base

Four steps prepare the microscope for storage: