MICROSCOPESHow to Use a Microscope

Microscope Drawings

Parts of the Microscope

Magnification, Resolution and Contrast

Types of Microscopes

HOW TO USE A MICROSCOPE

see handout for complete list

carry microscope with care using two hands only use coarse adjustment on LOW power return microscope with stage as low as

possible, LOW power lens in place and power off

MICROSCOPE DRAWINGS

see handout for complete list

use pencil and white paper use a ruler for all labels and place them on

the right of the drawing use appropriate size and scale stippled when required

PARTS OF A COMPOUND LIGHT MICROSCOPE 1 – eyepiece/ocular –

contains the magnifying lens to look through

2 – body tube – holds the lenses of the eyepiece and the objectives at a set distance from each other

3 – high-power magnification lens – used to magnify the specimen 40 x and see a small area with lots of detail

PARTS OF A COMPOUND LIGHT MICROSCOPE 4 – low-power

magnification lens –used to magnify the specimen 4 x and see a large area with little detail

5 – stage clip – holds the slide in place

6 – stage – holds the slide and a hole in the center admits light

7 – diaphragm – regulates the amount of light that passes through the hole and the specimen

PARTS OF A COMPOUND LIGHT MICROSCOPE

8 – base – supports the weight of the microscope

9 – arm – supports the body tube and adjustments and allows the microscope to be carried

10 – coarse adjustment knob – used to get the specimen in focus

PARTS OF A COMPOUND LIGHT MICROSCOPE 11 – fine adjustment

knob – used to focus through the layers of the specimen

12 – revolving nosepiece – holds the objective lenses and permits their interchange

13 – light source –emits light through the diaphragm

MAGNIFICATION

amount the lens enlarges the specimen

in a compound light microscope both the eyepiece and the objective lenses magnify the specimen

total magnification is the amount of magnification seen when looking through both lenses

total magnification = eyepiece magnification x objective magnification

MAGNIFICATION

Calculate the total magnification for the school microscopes:

Eyepiece Magnification

Objective Lens Magnification

Total Magnification

10 x 4 x (Low Power)

10 x 10 x (Medium Power)

10 x 40 x (High Power)

RESOLUTION

how well a microscope allows you to make out two different objects that are very close together

most people can see with a resolution of 0.1 mm or larger

microscopes allow us to see with a higher resolution

CONTRAST

how well you can tell the difference between cell parts or the cell and the background

to improve contrast scientists will stain cells

stains allow scientists to see the cell against the background of light

most common stains used are methylene blue and iodine

SIMPLE LIGHT MICROSCOPES

uses one magnification lens

beam of light travels through the specimen

living organisms

movement

true colour

magnification of 1000x

SIM

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COMPOUND LIGHT MICROSCOPES

uses two magnification lenses

beam of light travels through the specimen

living organisms

movement

true colour

magnification of 2000x

resolution of 200 nm

CO

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TRANSMISSION ELECTRON MICROSCOPE

beam of electrons travel through the

specimen

only very thin specimens

specimens are encased in plastic and the

plastic is shaved to get the thickness

required

dead organisms

magnification of 5 000 000x

resolution of 0.2 nm

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SCANNING ELECTRON MICROSCOPE electrons scan the surface of the specimen

and are reflected and magnified onto a screen to produce an image

image is 3-D

magnification and resolution lacking compared to transmission microscope

better contrast and depth than the transmission microscope

magnification of 300 000 x

resolution of 10 nm

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