microscopes- a brief introduction

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MICROSCOPE - AN INTRODUCTION Malathi Murugesan, I year M.D., Department of Microbio Chengalpet medical col Presenting By,,,

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a brief introduction about microscopes

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Page 1: microscopes- a brief introduction

MICROSCOPE - AN

INTRODUCTION

Malathi Murugesan,I year M.D., Department of MicrobiologyChengalpet medical college.

Presenting By,,,

Page 2: microscopes- a brief introduction

Replica of Marshall Microscope, c. 1700, by John

Marshall (1663-1725).

Page 3: microscopes- a brief introduction

Why Microscope,,,

Page 4: microscopes- a brief introduction

History of the Micro(organism)scope

• 1590 –first compound microscope

Discovery of Microorganisms.

Anton van

Leeuwenhoek (1632-1723)– first person to

observe and describe micro-organisms accurately

The way how he found micro-organism’s….

Page 5: microscopes- a brief introduction

Classical Microscope

A. OcularB. Body tubeC. Stage clipD. Revolving nose pieceE. ObjectiveF. ArmG. StageH. DiaphragmI. Lever to move stage clipJ. Course adjustmentK. Fine adjustmentL. Light sourceM. Base

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Parts of Microscope,,,• Eyepiece Lens:  the lens at the top that you look through.  They are

usually 10X or 15X power. 

• Tube:  Connects the eyepiece to the objective lenses.

• Arm:  Supports the tube and connects it to the base

• Base:  The bottom of the microscope, used for support

• Illuminator:  A steady light source (110 volts) used in place of a mirror.  If your microscope has a mirror, it is used to reflect light from an external light source up through the bottom of the stage.

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Cont,,,• Stage:  The flat platform where you place your slides.  Stage clips hold the

slides in place.  If your microscope has a mechanical stage, you will be able to move the slide around by turning two knobs.  One moves it left and right, the other moves it up and down.

• Revolving Nosepiece or Turret:  This is the part that holds two or more objective lenses and can be rotated to easily change power.

• Rack Stop:  This is an adjustment that determines how close the objective lens can get to the slide. 

• Diaphragm or Iris:  This diaphragm has different sized holes and is used to vary the intensity and size of the cone of light that is projected upward into the slide. 

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Lens

Objective lens Condenser Lens

Usually you will find 3 or 4 objective lenses on a microscope

It consist of 4X, 10X, 40X and 100X powers.

When coupled with a 10X (most common) eyepiece lens, we get total magnifications of 40X (4X times 10X), 100X , 400X and 1000X

The purpose of the condenser lens is to focus the light onto the specimen

Condenser lenses are most useful at the highest powers (400X and above). 

Microscopes with in stage condenser lenses render a sharper image than those with no lens (at 400X)

 If the microscope has a maximum power of 400X, you will get the maximum benefit by using a condenser lenses rated at 0.65 NA or greater

Page 9: microscopes- a brief introduction

Microscope Vocabulary• Magnification: increase of an object’s

apparent size

• Resolution: power to show details clearly

Both are needed to see a clear image

Page 10: microscopes- a brief introduction

Types of Microscopy

• Compound Light Microscope• Phase contrast microscope • Dissection or stereoscope • Electron Microscope• Transmission Electron Microscope• Scanning Electron Microscope• Flourescence microscope

TEM

SEM

Page 11: microscopes- a brief introduction

Light mechanism

• What is Light???

Visible light (commonly referred to simply as light) is an electromagnetic radiation that is visible to the human eye, and

is responsible for the sense of sight.

  Visible light has a wavelength in the range of about 380 nanometres (nm), or 380×10−9 m, to about 740 nanometres.

The natural agent that stimulates sight and makes things visible.

Used for illuminations…..

Page 12: microscopes- a brief introduction

Angle of Incidence

• Angle of incidence is a measure of deviation of something from "straight on“

Page 13: microscopes- a brief introduction

Snell’s Law

Snell's law (also known as the Snell–Descartes law and the law of refraction) is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass and air.

Page 14: microscopes- a brief introduction

Cont,,,

Refraction of light at the interface between two media of different refractive indices, with n2 > n1. Since the velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.

Page 15: microscopes- a brief introduction

Do light waves have amplitude???• Of course it has,

• Yes… Waves in general have three properties

Frequency (related to wavelength), Amplitude, and Speed

Freq- No of cycles.

• Frequency tells us how many waves are passing a point per second, the inverse of time.

• Wavelength tells us the length of those waves in metres, almost like adisplacement.

• If we multiply these two together, we are really multiplying 1/s and m… which gives us m/s, the velocity of the wave!

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Cont,,,

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17.

Lenses and the Bending of Light

• Light is refracted (bent) when passing from one medium to another

• Refractive index– a measure of how greatly a substance slows the

velocity of light , where c is the speed of light in vacuum and v is the speed of light in the substance

• Direction and magnitude of bending is Determined by the refractive indexes of the two media forming the interface

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Focal point and Focal length

• Focus light rays at a specific place called the focal point

• Distance between center of lens and focal point is the focal length

• Strength of lens related to focal length

• short focal length more

magnification

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The Light Microscope

• Many types– bright-field microscope– dark-field microscope– phase-contrast microscope– fluorescence microscopes

• are compound microscopes– image formed by action of 2 lenses

Page 20: microscopes- a brief introduction

Mechanism of Light Microscopes

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The Bright-Field Microscope

• Produces a dark image against a brighter background

• Has several objective lenses– parfocal microscopes remain in focus when

objectives are changed• Total magnification

– product of the magnifications of the ocular lens and the objective lens

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Microscope Resolution

• Ability of a lens to separate or distinguish small objects that are close together

• Wavelength of light used is major factor in resolution

shorter wavelength greater resolution

Page 23: microscopes- a brief introduction

Working Distance

• working distance— Distance between the front surface of

lens and surface of cover glass or specimen

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The Dark-Field Microscope

• Produces a bright image of the object against a dark background

• Used to observe living, unstained preparations

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The Phase-Contrast Microscope

• Enhances the contrast between intracellular structures having slight differences in refractive index

• Excellent way to observe living cells

Working Principle,,,

Page 26: microscopes- a brief introduction

Cont,,,

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The Differential Interference Contrast Microscope• Creates image by detecting differences in

refractive indices and thickness of different parts of specimen

• Excellent way to observe living cells

Page 28: microscopes- a brief introduction

Thanking YouThanking you